Tech Forum

In the early 60's, the Thunderbird with the sequential turn signals was all the rage. I had a 1960 Chevrolet Impala Convertible, and wanted to put in sequential turn signals. The tail lights had three lenses, the center one was clear for the back up lights, but would accept a red lens too.  So as far as the lights themselves I was all set. I went to the Ford dealer and asked at the parts counter for the turn signal blinker for the Thunderbird. As I was young and naive, I imagine that I thought I would simply connect it the same way it was done in the Thunderbird. Well of course no such luck, and the part was not returnable as it was an electrical part. So here is the short version of what I did, without any schematics, I too am 72 years old and this goes back 60 years or so.

The Thunderbird turn signal device consisted of a small motor to turn four cams. Three of the cams were used to light the lamps in the proper sequence and the fourth cam was used to keep the motor running until it returned to the home position. Somewhat like the windshield wipers on a car. I removed the standard turn signal blinker and placed a short across it, so that when ever the turn signal was on, I had power there for the entire time. The signal to the rear lamps was now either steady brake or steady turn signal. Of course this was not very useful for this application. However, the front turn signal lamps only have either steady power when the turn signal is on and zero power regardless of the brake switch. Exactly what I was looking for. I used the front turn signal to power the motor with one cam connected, to keep it running to the home position after the turn signal power was removed because the switch had returned to the off position. Now my only problem was to get brake power to the lamps when the brakes were applied and turn signal power for the three cams when it wasn't.

The simple solution to this was to simply use a multiple contact relay, one set of contacts for each lamp. The front turn signal power along with the power from the fourth return home cam was used to energize the relay. Of course I needed two relays, one for the left side and a second one for the right side. It worked as expected and I was the envy of the town, because I was the only non ford vehicle with the cool sequential turn signals. The whole mechanism fit inside of a plastic box about the size of a shoe box.

So that was the solution almost 60 years ago.  Today I would still remove the standard turn signal blinker, and place a short across the terminals to give me always on power when ever the turn signal is activated. I would still use the front indicator to tell me when the turn signal is activated, thus separating the brake signal. From there, I would either use some relay logic, or perhaps discrete logic, along with some timer circuits (555 comes to mind) or a microprocessor to generate the the necessary rear sequential signals. My choice would be a microprocessor, today they are very easy to use and program.

If the only input signal that you have is the 12V to the tail lights, you can't get there from here, for the scenarios that you describe, no matter how much "programming" you do or logic circuitry you design. You need to know the state of the brake pedal switch, turn signal switch and the hazard lights switch at their source and not modulated by the vehicle flasher module, which may be wired upstream of the switches.

Consider this scenario using only the 12V tail light signal:

1. At the first 12V tail light signal - All bulbs ON immediately. (any delay could get you rear ended if it is brakes or a quick lane change)
2. If the 12V goes OFF and then back ON within a time calibrated to the vehicle flasher module rate, then sequence bulbs #2 and #3 ON after delays. Use the 12V signal directly so they go OFF when it goes OFF.
3. If the 12V stays OFF for greater than 2x or less than 0.5x the flasher rate, reset the circuit and go back to step 1 .

This scenario should work in all cases except where you are pumping the brakes old school on ice at a rate that matches the flasher. Hopefully , a rare situation. This should be a fairly straight forward logic circuit with RC time constants and comparators or 555 timer ICs. Use pass-through for bulb #1 and relays for bulbs #2 and #3 on the normally closed (NC) contacts, so that a failure of your circuit still gets the 12V signal to the bulbs. (Fun Fact: Basic automotive flasher modules use current draw to determine blink rate. Which is why it blinks faster when you pull a trailer due to the extra bulbs. There are "heavy duty" modules that set the rate independent of current draw and are a direct replacement for most applications.) You will need the "heavy duty" one for your vehicle to get a stable rate to calibrate your circuit.

I used to own a 1972 Mercury Cougar with sequencing tail lights. Maybe you could get the control module from a junk yard. (All models 1973 and older - I don't know about newer).

I am not completely sure how you want the lights to act when the brake petal is pressed, and frankly I would use a PIC style device to implement this, either a basic PIC chip or one of the ones with a higher level programming language pre-loaded (Ardunio, etc).

But you want a way that does not use code. One way to do this would be to use the old standby 555 timer chip. They can be configured as a one shot, time delay device. You can chain several of them in a ring so that each will trigger the next one in the loop. So they will form a ring counter type circuit.

Then, the first 555 will have a steering diode connected to it’s output and then to the base or gate of a power transistor which drives the first bulb.

The second one has two steering diodes and they are connected to the base or gate of the first AND second power transistor.

The third 555 will have diodes that drive three such power transistors. Each of the power transistors is connected to one of the lamps. So when the first timer is triggered, the first bulb comes on. When the second timer is triggered, the first and second bulbs come on, and when the third timer is triggered, all three bulbs will light.

If you only want one light on for each step in the cycle, just eliminate some of the steering diodes. Additional steering diodes can be connected to the power transistors to activate them when the brake petal is pressed. Additional buffer amplifiers may be needed to get the polarity and current correct for this, depending on the vehicle’s system. The steering diodes will isolate the two functions, brake and directional signals. This does not allow turn signals to flash while the brake pedal is pressed.

An additional, exclusive OR circuit (CMOS logic chip) could be added between the steering diodes on each power transistor and the base or gate of the transistor. This would allow all three bulbs to light when the brake petal is pressed and then they would turn off one at a time if the turn signal is activated.

If this is done, then it would be best to use my suggested method for having only one bulb lit at a time by the turn signal circuit. Thus at least two bulbs would be lit when the brake petal is pressed.
You need to consider how to kill the lights when the turn signal is turned off. This could probably be done by adding three additional transistors to ground the timing capacitors of each 555 when the turn signal is turned off.

I can’t visualise exactly why you would want to do this since, on a car, they are discrete circuits. Perhaps it’s for a model? No matter.

You seem to have cracked how to flash and how to sequence the lamps. The problem seems to revolve around cross connection interference.

Have you tried isolating the circuit’s outputs by feeding the bulb through isolation diodes? With a 12V circuit, these won’t be noticeable, and allow the bulb(s) to be earthed as is normal practice. (Remember to select the diode to handle the inlet surge current through the cold bulb(s).)

You might not want to hear this, but the easiest, most expedient way to do this is with one of the cheap Arduino boards available from eBay. There are a myriad of power supplies, (12 VDC to 5 VDC DC-DC converters), and I/O boards, (relay or solid state), which will just plug together with, as they call them, Dupont cables. All of these are cheap, as in a few dollars. The Arduino IDE is free and with the most of the boards, a simple USB cable is all that is required to interface.

Now, while this may seem very complicated, there are tons of online tutorials. The end result is you get to learn something about electronics, programming, and maybe a new hobby.

The other plus is that you can end up solving your problem AND you also have the ability to make your lights do anything you want.

I found a $20 flasher module via a Web search for “turn signal light sequencer.” The device will flash as many as four lights. You’ll need one module for the left-side lights and another for the right-side lamps.

Creating your own controller with simple logic circuits would get complicated because only one signal turns a brake or turn light on or off. Thus, your circuit must distinguish between a constantly-on signal for braking and pulses for turning. You could use a small PIC microcontroller, but you don’t want to learn how to program, which I understand.

If you change your mind and want to start simply, look at the Parallax Propeller FLiP Module (or the Propeller QuickStart board) and use the free BlocklyProp programming tool. It doesn’t get any easier — you simply choose graphical “blocks” and stack them one on the other. Concentrate on the problem and let BlocklyProp create the code to program the chip.

I will use it. How much do you want for it?

I'll take it as I still use leaded solder.

Leaded solder is still available and widely used, both in aerospace and in the repair and rework of older equipment that was made with leaded solder. Many hobbyists including myself prefer leaded solder because it flows better and makes much nicer joints. As long as you don’t chew on it and are not disposing of millions of tons of equipment made with it there is not really a hazard in having or using it. If you don’t want it I would encourage you to give it to somebody else or alternately you could sell it on ebay.

Leaded solder is considered hazardous waste. If you want to get rid of it reasonably, you can take it to your local house hold hazardous waste. Contact your municipality and they should be able to help you out with that. HHW usually is only one or two days a year at your local collection site.

Most countries would consider it hazardous — as you surmise — and it should be disposed of responsibly, according to local regs. (Whoever accepts dead car batteries should take it for free?)

But should you get rid of it all? The fact that you have it at all indicates you’re interested in electronics, either from repair or construction. The important point I’m trying to make is that the two types of solder don’t play well together, so for reliability, older equipment should only be soldered with leaded solder (and vice versa.)

Do some Googling to check it out. Don’t use plumbing lead-free solder for electronics, either! If you’re giving up the hobby, then shame, but so be it.

If you are a hobbyist, why not just use it. Unless you are selling a product in high volume you’re not going to distroy the world. And it’s so much better than the lead free stuff.

Send it to me. Or to your local makerspace or electronics club (or robotics club, model train club, so on). Most of us prefer to work with leaded solder rather than lead-free for a whole host of reasons.

Officially you’re supposed to dispose of it at a local waste materials convenience center, but I just cant see it going to waste when so many of us are looking for leaded solder.

Take it to a metals recycling center that deals in lead (usually those that take old lead acid batteries). It is generally considered hazardous waste, so don’t throw it away in your trash bin.

You might look into see if you have any kind of municipal or county hazardous waste collection facilities as a part of your home garbage pickup service as well. They may have a drop-off location that can take it.

Finally, you might consider donating it to a local maker or hacker space; a lot of people love leaded solder over non-leaded, due to certain properties it has versus the other.

Instead of throwing it away which is probably illegal, especially if you live in CA, why don’t you give it to other hobbyists. Would you take the cost of shipping to send a spool?

I don’t do any commercial work, so using leaded solder is no problem. The cost of solder for a lot of us retired hobbyist is a lot. Also, what diameter is the solder and does it have a rosin core?

It's a crapshoot. I worked on 3 Chinese sets in a row that were junk, then came to one that was excellent. Other techs report similar experiences.

Bear in mind that the Arduinos in those kits are clones at best, and counterfeit’s at worst. What’s the difference? Well, a clone is one that could be identical in every way to a real Arduino, but is branded differently “SunDuino,” with that brand’s own logos, styling, etc. A counterfeit, on the other hand, seeks to make its product look as close to the official Arduino (i.e. color, branding, logos, screen printing, color of parts on board, etc) as possible — to confuse the buyer and make their product seem more legit.

That said, whichever you choose is between you and your conscience. Honestly, the quality is going to be nearly identical between that of a clone or otherwise; usually — not always. Pay attention to reviews and such is my best advice. SainSmart, DFRobot, and SeeedStudio are all good sellers of clones.

Something else to keep in mind about these Arduinos: they typically use the CH340 USB chipset for the virtual serial link. This is a well supported chipset, but its something to consider.

An official Arduino uses a secondary ATMega16U2 microcontroller for USB communications. Prior to that, they used the FTDI chipset for USB serial comms. Chinese clones continued to use the FTDI chipset even after the Arduino switched to the 16U2, likely because it was cheaper. FTDI then released a driver update (or something like that) that bricked unlicensed versions of the chip, and caused a lot of grief. That basically is what caused the Chinese clones to switch to the CH340 chipset (plus, it was much cheaper).

As far as everything else in the kits, quality varies, but for the most part, its fairly consistent — again, check reviews.

The biggest problem with these kits will typically be a lack of any kind of instructions, project ideas, or any kind of datasheets on the components. Most of the time, these kits are meant for those who are very self-sufficient in hardware and software. If you’re lucky, you’ll get a CD or a URL of PDFs and software, but I would caution against doing anything with it, particularly if you are using a Windows box, as such CDs and software have been known to be vectors for malware.

Finally, as you have probably noticed, there are sellers out there offering some seemingly “weird” kits or microcontrollers, which you may wonder what the use of them is for.

Most of the time, these controllers are meant to serve as platforms either for hacking, cloning, or counterfeiting well known tools based upon the same controllers (either current or older versions). For instance, there are plenty of clones and “bare” development boards which can be configured to act as a Saleae logic analyzer. Others are meant for other similar products, and some are meant just for experimentation (there’s an interesting set of microcontrollers out there based around a hopped-up 80C51 clone). Oh, and some are meant for experimentation creating flight controllers for quad-copters, too.

Lastly, you may have noticed some of the “rival” ARM-based SOC boards rivaling the Raspberry Pi (such ase the Orange Pi and the Banana Pi, among others). These can be extremely cheap and very powerful alternatives to the Raspberry Pi or Beagle, but keep in mind that they tend to be very community supported in that while they are alternatives, they are typically more popular with hardware hackers in China, so the english-speaking community is likely smaller, and support isn’t as good; plus drivers and such for the boards can be hit-or-miss.

Basically, what I’m saying here is that if you want something closer to plug-n-play, stick with the official Raspberry Pi. But if you want to go out on a limb, these alternatives can offer an interesting reprieve — if you’re willing to dedicate more time.

I’ve only built one kit from China: an AM/FM receiver kit for a small pocket radio. The directions left much to be desired, I had to guess at how to put some parts in. I’m still not sure I put the tuner section in correctly, since the FM section starts well below 88 MHz and ends at around 88.5 MHz. I still need to look over the schematic again to see if it was a misinterpretation of one of the parts installations or not.

I don’t like the quality of the case either but it does sort of work and did so the first time I turned it on.

Now, I have dealt with a number of Chinese companies and had some very interesting experiences. I’ve had returned parts returned back to me along with a full refund. After three months of daily email, I simply gave up and kept the parts as well as my refund, since I couldn’t get them to understand that I’d received a refund and didn’t need the parts.

The bottom line is, as long as you pay using PayPal you are safe and can get your money back as long as you keep good email records and supply PayPal with a full explanation of the problem, such as the item does not work as advertised or it doesn’t meet the seller’s own published specifications. I capture an image of the site’s own specifications on the item just to be safe.

You asked an either/or question. The answer is YES. There are problems with many of these kits. See question 1171 for an example. They also usually have terrible or non-existent documentation. But they do have the material in them to support a great many projects and demonstrations for an incredibly low price. So if you are on a tight budget they are well worth the problems.

A lot of the products from China are cheap clones, some are of good quality and some are not. I buy different type of modules for the Arduino Uno to try, I am working on a TEA5676 FM receiver.

I also support a lot of American electronic parts stores in the USA. I like ADAfruit, as they have a lot of tutorials on the products they sell. This helps greatly with the learning curve on the newer electronics.

You might try old auto-focus cameras and similar equipment. Old micro-cassette players too. These all generally have a bunch of small shafts and pulleys; you could take one of the small pulleys and add a miniature o-ring as a tire.

Another possibility, maybe even better, would be those small micro remote control cars, which were popular a few years back. Or maybe small slot-cars or n-gauge trains?

Another possibility for a tire might be a slice of pencil eraser. Super-glue it to a small piece of piano wire or similar for the shaft.

The main reason to use an analog (i.e., moving coil) meter is that it's much easier to watch a moving needle than changing digits (even if the DMM has a moving bar in the display). This is especially true when trying to peak an amplifier or similar AC circuit. It's also better to watch a moving needle when testing a potentiometer with suspected dropouts as the needle will visually react faster than even the fastest updating digital display on a decent DMM. Finally, for voltage/current measurements, analog meters need no batteries to operate (resistance measurements is a different story) and they're great for Go/Nogo testing of the presence/absence of a voltage (within the limits of the meter's ranges).

I suggest getting an inexpensive analog meter (ike this one from Sears: www.sears.com/craftsman-analog-multimeter/p-03482362000P?plpSellerId=Sears&prdNo=16&blockNo=16&blockType=G16#) and experimenting with it. Be aware the sensitivity of these meters is usually 2 Kohm/volt (rather than 20 Kohm/volt for a good Simpson VOM), but it's good enough for you to do your own visual comparisons. Plus, you won't be out too much money for one of these units AND, as long as you don't install the battery for doing resistance measurements, you can keep it in the glove box of your car for doing voltage checks if needed.

In the end though, it's up to you to make the final decision on analog vs. digital meter displays for your use.

Audio work can require the measurement of voltages down to the millivolt range. It can also require measurement of varying signals such as voice and music. To best measure these use an “AC VTVM.”

This is an electronic device with a large analog meter driven by an electron tube. They usually have a high input impedance and wide frequency range — often into the 100 kilohertz range. Their input voltage range is usually from 1 millivolt full scale to 300 volts full scale. The meter has scales in both volts and dB — with dB making it easy to measure amplifier gain.

Want to know what the output voltage of a microphone will be for a particular sound? Put the microphone at the desired location in relation to the sound and hook the microphone directly to an AC VTVM. Then just watch the meter scale. (A digital meter will just wildly blink random numbers.)

As an audio engineer, I find that an AC millivolt meter, calibrated in decibels, is essential for audio engineering and repair. For example, to validate the dB attenuation of a Linkwitz-Riley crossover network, or to gauge flatness of a preamp. My 80’s vintage Leader LMV-187 is what I use for this work.

That said, it is easy to build much cheaper and available alternatives. Dual channel VU meter driver boards, and decent VU meters calibrated in dB, are available on eBay. Frontend one of these boards with the ‘Low cost PC Two Channel Oscilloscope’ circuit of the August 2016 N&V, and one has a decent AC metering system for audio engineering. Be sure to AC couple the input to the circuit, for example with 2.2uF non-polarized electrolytic capacitors.

I use my DMM’s for checking power supply voltages, etc. But for audio signal level work, an analog metering system, calibrated in dB, is indispensable.

New analog VOMs are certainly available, but quality is likely nowhere near what used to be standard. What the cheap DMMs won’t show you are fast transient signals; they will either average out the spurious signal (you won’t see it), or they will just completely miss it, due to a slower “sampling” rate.

A high-quality Fluke DMM can be a good choice, but there isn’t any reason not to have an analog meter on your bench, if you can find a good one (tested, calibrated, and known to work well), along with a Fluke.

Sometimes, the slight tremble (noise or hum over the signal) of an analog movement can be seen better by a human than a DMM can update. But for most things, you could use the Fluke (heck, for most things, you could just use an el-cheapo free-with-coupon Harbor Freight throw-away).

Another option to consider, depending on the signals being looked at of course, would be a digital o-scope; being able to sample a signal over a period of time, then going back and reviewing it can be very helpful in tracking down certain problems that can’t be seen otherwise, using other tools.

The use of analog versus digital to me is a personal choice. I work in the 2-way radio field and personally prefer analog meters for several reasons; the first is that it is easier to detect a peak or a null with a needle on a meter than it is trying to read changing numbers on a digital display. In fact, I have never seen a grid dip oscillator with a digital display.

The second reason is that while working on a circuit board and looking for voltages, I can glance up at an analog meter and watch the needle move, and with the proper range set, I have a good idea what the voltage is with just a glance. With some analog meters such as the B&K 290 electronic VTVM that I use on the bench, there is a scale on the bottom with zero centered mid-span which allows me to see if a voltage/current varies from what I have set as the standard I am using, which allows me to set voltage/current to that standard.

While I am an ‘analog guy’ there are times when I use a digital meter. When setting VCO voltages you need a digital meter to accurately set the voltages. Another use where digital is better (in my opinion) is reading the values of resistors and capacitors. A DMM has the advantage of reading capacitors, which analog can’t do. Although, it can be a pain to read resistors on an analog meter due to the logarithmic scale and crowding at the high end of the scale, it does excel at testing pots to see if the operation is smooth by watching the needle.

On my bench I have the B&K 290 analog electronic VTVM, a NLS TT-21 digital meter and for field work a Triplett model 60 VOM. What works for me or someone else may not necessarily work for you. As I said, it’s based on what you prefer and what your requirements are. I would suggest seeing if you can borrow a digital and analog meter, use them and see what works best for you.

I will offer this suggestion if you do go the analog route, go for a meter that has 20K ohms/volt or better, the higher the ohms/volt the better as it will not load down a circuit under test as a lower range would.

There are many differences between DMMs and VOMs. The two which might justify the old timers advice are that VOMs have lower input impedance than the typical DMM and the dial display of a VOM display is easier to interpret for noisy or changing amplitude signals than a digital display. The higher input impedance of a DMM may make readings from old documentation based on using a VOM slightly inaccurate.

Neither of these characteristics really justifies spending lots more money. Many DMMs include a bar graph display which emulates a dial, mooting this difference.

Finally, analog meters from lesser makers are still available in economy markets and auction sites. If you do find those two differences compelling you can satisfy that need at costs comparable to most DMMs.

The question is not Average vs RMS. When dealing with tuning; the question is measuring of Peaks and Deeps. You can’t measure Peaks and Deeps with digital Voltmeter, to do it you need an analog device.

About 50 years ago, Fluke came out with a nice digital multi-meter that couldn’t be used for tuning. After some time Fluke added an Analog Bar-graph that helps a lot for tuning purposes.

Try to look for Fluke Series 170 and you will find what you need. Buy the way, tuning is mainly done in RF equipment and not in audio.

On web page https://www.fcc.gov/media/radio/am-query enter the FCC Facility ID Number which is usually 4 or 5 digits. Note this is NOT the >>> FAA <<< tower number which is often shown on signs posted at tower sites.

For example, I entered 9642 and it properly brought up: WCCO AM 830 kHz ND1 Unlimited A A LIC MINNEAPOLIS MN US BL-- 50.0 kW 9642 CBS RADIO MEDIA CORPORATION with a link location of: https://transition.fcc.gov/fcc-bin/amq?list=0&facid=9642 This link showed a web page with: “WCCO MN MINNEAPOLIS” and with all kinds of details and links.

So let’s say you are motoring about the countryside one fine day and you spot an interesting tower structure. Look around the entrance area and you should see a sign with the FCC Tower Identification Number on it. Let’s use number 1027514 as an example. Go onto www.fcc.gov/ and:

1. Click the Licensing and Databases tab. You’ll be presented with a list of about 25 databases listed by their acronyms. Some of them are intuitive. Others, not so much.
2. In this case, Click on ASR (for Antenna Structure Registration). Partway down the page you’ll find Search with a choice of either Registrations or Applications.
3. Click on Registrations and a new window opens. In the upper left corner is a field you enter the registration number. While you’re here, you can check out the other possible searches such as lat/lon, by state, etc.
4. Enter the registration number and hit Submit. Note that this takes a whole lot longer to describe than to actually do it. A new window opens with the results, typically one line, but a fact-filled line. We now know the FCC File Number, the owner (in this case, WLAJ-TV), lat/lon, city and tower height in meters (307 meters or a little over 1000 feet). By the way, you can also get here by going to www.fccinfo.com/ where the good folks at Cavell, Mertz and Associates have an easy-to-use database front end and a nifty Google Earth plug-in that will give you the callsign for a station associated with a broadcast tower. Note - broadcast, not cell, two-way or other utility tower.
5. On the ASR Results page, click on the Registration Number. A new window opens, chock full of good information.

Another way to go about this is on the FCC home page, click on ‘browse by Bureaus & Offices’ then on the Media sub-tab. The Media home page will appear. Now, along the left side you will be presented with a list of choices. You want CDBS Search. You’ll then be presented with another list of choices which should be fairly self-explanatory. As an example, choose the first selection which is Search for Station Information (as of the date I’m doing this). The new window is a whole bunch of search fields but to keep it simple the first line is Call Sign. In that field, enter the call letters. Pick your station of interest and type it in there. Example - WLW and hit the Submit Station Search button. A new window opens with the results, which are fairly skimpy at this point. But on the far right of the results is a link labeled Click for Details. Another results window opens with more links to more information. But now we can get into the good stuff.

On the Bureaus & Offices / Media home page, select Electronic Filing and Databases along the left side. The new page that opens offers another list of choices, one of which is AM Query, among others. Hit that one and a new query search opens. On the first line enter WLW. Further down, just above the Results buttons you choose how much information you want. Choose the AM Query (detailed output + CDBS Links) menu item and hit either the Results To This Page/Tab or the Results To Next Page/Tab buttons, depending on your preference. You’ll get everything you ever wanted and more. If you’ve got the time, you can easily spend hours looking up all kinds of arcane things.

POTS ring generator modules are readily available prebuilt. The Tele-Q 70-9100 at www.musson.com is a self contained ring generator with simple pushbutton operation.  Viking Electronics model DLE-200B www.vikingproductstore.com  is a two way phone line simulator that will ring one phone when the other is picked up and provides loop current to power the phones.  

For theatrical use this will ring the phone on stage but the ability to also talk on the phones may help the person on the phone have a more realistic sounding phone conversation.

I found this at: www.electronicspoint.com/threads/generating-a-20hz-90v-signal-phone-ringer.61314/ Seems like it would work fine for stage use.

I had an old Post Office local system ring generator that did the job very simply. It had a transformer with a split winding on one side, and a single winding on the other. The split windings were linked in series by a 2uF paper capacitor, and a single diode (IN4007 style) was in series with one of the outside terminals. The diode half wave rectified the mains going in, providing the transformer with half mains frequency pulses (25Hz in the UK). The cap between the windings provided rough tuning, which took the waveform back to something approximating a sine wave. Out of the other side of the transformer came a reasonable sine wave at about 80V p-p.

I guess that the same thing could be reproduced now using a split primary power transformer, with a secondary of say 40 - 0 - 40. The value of the cap could be played with a bit for best wave shaping to suit the tranny. I doubt that you would notice the frequency being 30Hz US or 25Hz UK. Arfa Daily, Oct 13, 2005

It's called a ringdown circuit. Here's one assembled that would work, but if you search using that term, you should find something. www.sandman.com/simulator.html

eBay has a Black Magic Ringing Generator for $26. A pushbutton can be used to intermittently connect four “D” cells to the input of the Generator and it will ring the phone. Be sure to hook the battery to the Generator with the correct polarity shown on the label. Connect the output of the Generator to the phone’s red and green wires, but you must also put a 330 ohm resistor in series with one of the output wires to the phone.

To be realistic, the phone should be made to ring for 2 seconds, off for 4 seconds, on for 2, off for 4, etc. Be sure to test the setup at home before moving it to the stage.

Well, years ago when I was involved in theater, we just connected the ringer to regular 110V 60 Hz utility power, through an offstage switch. You might have to futz with the clapper spacing and spring tension to get a good ring. We had a regular telephone bell in a small box which we rang, we hid it on the stage near the set phone, which wasn't connected. If you want to ring the actual bell in the phone on stage, I'd suggest using a 1:1 isolation transformer for safety. One time during a rehearsal when there was a phone on set that an actor was supposed to dial, for a spoof we connected it to a phone line. When the actor picked it up and heard the dial tone, he completely lost it...

For voltage, use a bunch of NE2 neon bulbs wired in series on a long wood stick. Each lamp lit stands for about 100 volts. For frequency, the coil probably operates at or below the broadcast band. If you can't hear it on a standard AM radio, buy or borrow a set with the long-wave band. None of this is lab-quality but I assume you want cheap and easy.

Simplest is a standard (cheapest bimetallic) house thermostat, a battery, and a simple DC bell! You don’t have to drill any holes or screw anything up, and the wire can be taken through a window into the house. I’m sure you could also rig up something like an arduino with hats and bluetooth or Wi-Fi with phone messaging, but unless you want to do extensive datalogging, I can’t see the point...

But that’s often beside the point in hobbyist systems.

Sounds like a job for the Raspberry Pi 3 computer connected to a DS18B20 temperature sensor with Cayenne software installed on both the Raspberry Pi and mobile phone. Cayenne is a software platform from MyDevices that acts as a gateway to the Internet of Things (IoT), the service is free. You can view temperature data from your mobile phone, or configure Cayenne to send a text message alert when the temperature drops below a set threshold. The Raspberry Pi can be connected to your home network using Wi-Fi or wired connection.

There is a wide assortment of voltage regulators available today, both linear and switching styles. The switching regulators are generally more efficient, but the question is about a linear regulator so I will stay with that.

Three concerns are brought into this question: reliability, efficiency, and accuracy. And it appears that this is going to be used with a battery.

First, a battery, by itself, is a fairly well regulated source. But there are two problems that are generally of concern with using a battery by itself. First, it may be hard to get a battery voltage that is what the circuit needs. For instance, if you are using 5V logic chips, then you are not going to find a 5V battery.

Second, the battery voltage will decrease with use: it will run down. This may not be desirable. But many logic circuits as well as many linear ones can run very nicely on bare battery power. CMOS logic chips can use supplies over a wide voltage range, so a 6 or 9V battery can be a good choice.

If you don’t really need a constant voltage over the life of the battery, a series resistor or diode can drop a fixed amount of voltage to bring the battery voltage down to the level needed by the load. But that voltage to the load will change as the battery runs down.

Figure 1

Linear regulators are of two general types, series and shunt. The series, linear regulator uses a series resistance that is controlled in a manner so that it drops the excess voltage from the voltage source, leaving only the amount desired for the load. The shunt regulator has a fixed, series resistance and diverts or shunts enough current to ground to bring the load voltage down to the desired value.

Figure 2

Another thing that must be considered when discussing efficiency is the amount of current that the regulator circuit itself needs for it’s operation. So, for instance, the series regulator circuit actually looks more like this.

Figure 3

Assuming that a regulator is needed and sticking to linear types, there are several choices, including the zener diode and IC types mentioned in the question. A zener regulator is a very simple form of voltage regulator. The circuit looks like this:

Figure 4

The theory is simple, the voltage drop across a zener diode will be constant so the series resistor drops the remainder of the supply voltage and allows the amount of current needed for that condition. The thing to notice here is that the voltage drop across the series resistor is approximately constant if the supply (battery) voltage is constant. So, according to Ohms law, the current through the series resistor is also constant. That current is the total current in the circuit and it is divided between the load and the zener diode.

The design of a zener regulator works like this:

1. Find the MAXIMUM load current that will be needed. It is important to find the maximum value, because if the current ever exceeds this value, the zener regulator will drop out of regulation and the voltage across the load will be lower than the design value. This is I_L.
2.  From the data sheet for the zener diode, find the quiescent or lowest operating value of current that is needed for the diode to operate at the zener voltage. This is I_z.
3.  Add I_L and I_z together to get the total operating current. I = I_L + I_z
4. R_s must drop the difference between the battery voltage and the desired load voltage. V_s = V_b - V_L. And, again using Ohms law, R_s = V_s / I
5. The zener voltage of the diode is just the desired load voltage. You are probably going to have to do some rounding.
6. You must calculate the worst case power consumption in both the series resistor and in the zener diode. For the series resistor this is simply P_r = V_s x I.
7. For the zener diode it is when zero load current is being drawn so: P_z = V_z * I.
8. It is good practice to multiple the power values by a safety factor. A 1.5X to 2X figure is generally used. The accuracy of a zener regulator can be seen on the zener’s data sheet. Look for a graph that shows the zener voltage plotted against the current. I would not be surprised by differences up to 10%, or even more. This is in addition to the tolerance value assigned to the zener diode.

A zener regulator will be as dependable as the two components used: the series resistor and the zener diode. The reliability of these will both be heavily dependent on the amount of heat generated in them. This will, in turn, depend on the safety factor I mentioned in step 8 above and also on the proper cooling of these components. A heat sink is highly desirable if the current, I is large. An IC, series regulator has a circuit something like this.

Figure 5

The design is very simple. The IC is connected in series with the power line and to the ground reference. In some cases where a different output voltage is needed, a resistor network can be connected between the IC’s output, ground, and the reference (bottom) terminal on the IC. The values of the capacitors are given on the data sheet. In the case of a battery supply, C1 can generally be omitted and a good value for C2 is often 0.1uF. R_s is an optional, series resistor that can be sized to drop part of the battery voltage when the load voltage is a lot smaller than the battery voltage. This decreases the amount of power that must be dissipated in the IC and therefore increases reliability. Again, calculations of the worst case power dissipation in both the IC and the optional R_s is needed.

If R_s = 0, then Pic = I x (V_b-V_L). This calculated power must be less than the rated value of the IC package. Keep in mind that different IC packages may/will have different power ratings. Adding R_s is one way of keeping the power dissipated in the IC within this limit. If R_s is used (not zero Ohms) then the power calculations get more complicated. The value of R_s will be chosen for the maximum current situation and that will be where it’s power dissipation will be the most. Pic should also be at a maximum at that maximum current point, but I would check it at the minimum current and also around the half way point, just to be sure.

The efficiency of any linear IC regulator will be better than that of a zener regulator unless the zener is always operating with a maximum load current. When the load current decreases below it’s maximum value a zener will simply draw more current and keep the total power that is dissipated at a constant value. The IC regulator will draw a varying total current that changes as the output/load current changes. Therefore it is generally a lot more efficient.

As for life or dependability, IC regulators are generally as dependable as any other semiconductor based component. Since the current passes through them, they may be a bit more susceptible to surges than a Zener style regulator because transistors will fail faster than resistors. But if they are properly designed and installed with proper heat sinks, they can last for many decades. I would not hesitate to use an IC regulator in this application. If you want even higher efficiency, a switching regulator can probably provide that. Reliability may be somewhat lower, but not a lot.

Accuracy of IC regulators, both linear and switching, is generally excellent. They all use feedback techniques where the output is sampled to provide the correction signal to the series element which controls the output voltage. The degree of accuracy can vary with the internal circuit details, but numbers like 3%, down to 1% or even better are common. Again, as with the zener, the rated accuracy and the accuracy variation with circuit conditions are separate values so an IC regulator with a rated accuracy of 5% may be capable of holding the output value to within 1% or even better.

The LM317 that you mention is an adjustable regulator design. It requires that you use additional resistors to bias the reference pin for the output/load voltage you want. This can be an advantage if an odd voltage is needed but you can also get similar, three terminal regulators that have fixed output/load voltages and do not require those external resistors. Look at the 78xx series for positive regulators or the 79xx series for negative voltage ones.

The LM317 appears to be about 5% in accuracy (you also need to add the error from the resistors used for the adjustment, but you could get some 0.1% resistors to manage that). A quick look on digikey shows plenty of 1% zeners so that path may offer more accuracy.

If your load is fairly constant, your zener circuit can be tuned so the zener will just barely turn on with the expected load. But if the load goes down, the zener will eat power to keep you regulated. There are some other parts out there that offer better accuracy. Check out the LT1460: 0.125%! (but only ensures 20mA output)

The LM317 would create a more accurate voltage; however, that may not be the best way to go. Not knowing what voltage in and voltage out you have, it’s hard to say, but the LM317 will scrub off the excess voltage as heat. However, there are boost/buck converters available for not much money (I bought four little boards based on the LM2587 for about $7.50 each off eBay, for instance) that will conserve the current (minimal heat, minimal waste, minimal extra battery usage) and keep the voltage even more accurate.

For perfect usage, team one of those up with a zener secondary regulator, so that you have a minimum of wasted current through the resistor feeding the zener and your circuit; that way you have both worlds working for you.

3-terminal voltage regulators, such as the LM317, are very accurate, and are suitable for most applications. You might want to consider a fixed voltage output, low drop-out type, 3-terminal regulator such as the 78L00 series, made by several different manufacturers. The low drop-out minimizes power loss — for example, you can obtain 5 volts out from 6 volts in (4 x AA batteries). However, the purpose of any voltage regulator is to create a stable fixed output from a variable input. Thus the regulator must dissipate power, and you must observe the power rating of the regulator, or it will overheat and self-destruct.

Are you looking for stability or reliability? The battery is reliable but not so stable because the voltage drops as the charge is depleted. If you have a full time battery charger attached, the stability problem goes away. The zener diode has a rather high impedance, up to 100 ohms for those under 6 volts and lowest at 6.8 volts. If you have a 6.8 volt zener running at 20 mA with an impedance of 25 ohms, and the load varies 10 mA, then the voltage will vary: delta V = Ro * delta I = 25 * .01 = 0.25V. The LM317 on the other hand has an output impedance in the order of .05 Ohms and you can set the voltage as accurate as you need using the schematic on Figure 5 of the data sheet. The voltage should stay within 1% over time but you can reset it periodically if you want. You should have a minimum load of 10 mA on the LM317 for good stability and don’t run at max current if you want good reliability.