Tech Forum

A 10 watt laser is capable of permanently blinding a person and possibly starting a fire. Mounted on a motorcycle, it would be totally illegal. No one in his right mind would get involved in this project!

It is my understanding that "Variac" type transformers do not provide isolation from the input power. They are basically tapped coils. In order to safely provide isolation they must be connected through a 'true" transformer. Depending on output stability requirements, you may be able to use a Cockroft-Walton voltage multiplier circuit through an isolation transformer. Check Wikipedia for "Cockroft-Walton" and "autotransformer."

You want to be extremely cautious experimenting with high voltages as they are lethal and can be fatal. Rather than trying to construct a high voltage supply, which could be dangerous, you might consider a variable transformer such as the Volteq #1KVA_110V/250V (www.volteq.com), which costs about $70. This transformer plugs into a standard 120 VAC outlet and provides an adjustable output from 0 to 250 VAC, and provides isolation from the AC power grid. If you want DC voltage, you can construct a simple bridge rectifier circuit. However, there are many more interesting projects that use 5 - 12 volts, and I suggest you pursue some of them instead.

Correcting Bob Stewart's answer: The variac he mentioned "VOLTEQ 1KVA VARIABLE TRANSFORMER VARIAC 1000VA 0-250V 110V INPUT" does NOT provide insulation from AC, as confirmed by Volteq. I suggest connecting such a variac only to an outlet with a Ground Fault Interruptor (GFI).

You didn’t indicate how much current you are expecting from the supply? Searching the internet I found the referenced schematic for a 300 VDC variable voltage supply that will deliver up to 100 ma. Circuit is for 220 VAC mains but we can substitute a step up transformer for operating with a 120 VAC mains. I have attached a parts list reference from Digikey that should do the trick. Due to the high voltage involved, you should put the components inside an enclosure, such as a Bud Industries box and bring the output up to a couple of banana type jacks or terminal block. You can also mount the pot on the outside of box and add a knob to it. Transformer is the most expensive component and can be sourced from other suppliers if you need to reduce costs. Hope this helps!

Schematic: www.eleccircuit.com/the-variable-high-voltage-power-supply-0-300v/
Parts List: www.digikey.com/short/327wpp

I would try either a magnetic field disruption sensor (long iron core coil monitored by a hall effect sensor) or a security type passive infrared detector (frequently available cheaply from electronic surplus outlets).

A couple of years ago I wanted to know how many cars were driving past my house each day so I built a counter for about $140. Here is the link to the 12 minute Youtube video describing how I did this: www.youtube.com/watch?v=Tw0P2DtB8Yo.

In addition to the car count, the laser detectors that I used also allowed me to acquire direction and speed. I saved the data to a SQL server and rendered the data on a webpage using highcharts (details in the video). This required a PC to be running all of the time (about 90 watts). I have now replaced the PC with a Beaglebone Black and use a MQTT listening service called mosquitto to acquire arduino data and pass it to the mysql database.

Programming and rendering is being done with Node-Red. I hope to develop a video with that configuration soon. Best of luck and please let me know if you have any questions.

This has been done before by several folks using a tube counter approach. The drawback is that you need to lay a tube across the roadway, but if this is OK for your project, this is the way to go. It’s the same way that professional traffic counts are often done. Two links on projects are https://hackaday.io/project/4567-traffic-counter-road-tube and www.tomorrow-lab.com/lab16.php.

Ultrasonic sensors might work if you you can put the sensor very close to the lane in question (e.g., if you just need to detect traffic on the nearest lane). Otherwise range becomes an issue and cost increases for longer range sensors. This site has a project that did just that: www.chris-sheppard.com/?page_id=40.

Radar rangefinders are the next step up for range if you can’t use a tube, one example would be something like the LIDAR-Lite 3 Laser Rangefinder, but you’re now using a >$100 sensor. There’s 3 pages of discussion on this topic on the arduino forum: https://forum.arduino.cc/index.php?topic=298000.30.

They're compatible; what you're seeing is the leakage current on the output of the X10, which is still enough to cause the LEDs to light up barely (and which isn't visible on incandescents.) If you truly want the LEDs to go out, though, you'll have to look for something better than the old X10 designs.

LED's use much less current than incandescent bulbs. Even just a few milliamps of leakage current through the X-10 modules can be enough to keep them glowing quite a bit. As a workaround, I've gotten around this problem by putting a low wattage (like 15 watts) incandescent bulb into a second socket.

Conventional x10 switches require a small current to run through the load (i.e. an incandescent light) in order to work correctly. For non incandescent loads such as CFL or LED lights you need a x10 switch specifically made for them. I currently use a WS13A x10 wall switch and also an XPFM x10 fixture module to switch LED lights (and CFLs). These x10 switches are not dimmable though. In general, LED lights need a dimmer specifically made for LED lights. I have had a good success with Lutron CL digital dimmer (e.g. MACL-153MH) as a manual dimmer but I do not know of an x10 compatible dimmer designed for LED lights. Perhaps someone else knows of one that will work.

I go through this problem whenever I use x10 in a small project. x10 appliance modules need some kind of load resistor, but due to the 110VAC appearing when it turns on, I do not advise it. Instead, a batter way to solve it is to connect a 110VAC relay parallel to the LED bulb. If you want to use a resistor 33K 1W will be OK (I tested up to 42K that works), BUT be very careful about insulating the wire leads. I tested both methods (resistor turn on only a second in on state), they work perfectly.

I wonder if Mr. Casas (or a neighbor sharing the same utility transformer) has recently installed a new central air conditioning system. Many of these systems employ a condenser (the outside unit) having a variable-speed fan. The fan is a three-phase motor powered by rectifying the AC mains power, then using an inverter circuit to convert the DC bus voltage into a three-phase AC voltage. The fan provides tachometer feedback so that the inverter provides three-phase power at the frequency needed to maintain fan speed to the degree desired by the control circuitry.

The inverter operates using pulse-width modulation techniques. A chopper frequency in the range cited — six to eight kilohertz — is not unreasonable, being sufficiently high to be significantly greater than mains frequency yet low enough to avoid the magnetics and copper losses that would otherwise occur if the frequency were higher.

The problem is that some of this chopper operation may be leaking back into the AC mains supply. The DC power filter capacitor(s) in Mr. Casas's radio do an acceptable job of smoothing the AC mains-frequency ripple; for cost reasons, however, there is no reason why the manufacturer would have chosen capacitors having equivalent series resistance (ESR) sufficiently low to filter kilohertz-range noise.

My suspicion is that Mr. Casas's radio is receiving power-line-conducted chopper noise. Since it comes via the power system, it will be presented to the radio's audio amplifier regardless of the volume control setting.

I have found that a light dimmer can cause buzzing on the AM radio band. If you tune to a strong station that will usually drown the buzzing.

This sounds like interference that is coming from some other device that you probably placed nearby the radio, like a cell phone charger or dock. Sometimes, LED lamps can create nasty interference. So can flat screen TV sets and computer monitors. (Even when they are OFF!) Try unplugging various devices and eventually, you should be able to find the culprit. The other option is to use a transistor radio, and walk around to see where the noise gets worse. This is how I found interference in the past.

I used to design circuits for military applications and in that environment, a voltage rating double the expected maximum was considered adequate. In an automotive application, the spikes from the starter can exceed 60 volts, so you need to keep that in mind and provide isolation.

Ripple current is another capacitor parameter that needs to be addressed. It turns out that ripple current rating increases with voltage rating, so you might use an electrolytic cap with 10 times the needed voltage rating just to get the ripple current rating.

In general, the MTBF (mean time between failures) is calculated based on the stress on the component.  A component (resistor, transistor, transformer, etc.) that is rated 70 degrees C but is running at 150 degrees C will have a short life, but if it’s running at 30 degrees C the life will be normally long.

I remembered that I had designed and built a gadget that may be the answer. A hand-drawn page is attached, a bit crude but it says it all.

The piezo buzzer will sound after 64 blinks. Pulsing 12V will charge C1 via D2 + R4 (soften the charge spike). C1 supplies power to the seven-stage ripple counter. It holds enough charge for about three seconds. Pulses are fed to the counter input via D1 and R1. C2 will prevent spikes; R2 will discharge C2; and D2 will prevent input from going higher than Vdd + 0.7V. Output Q7 will go high after 64 pulses. R3 will limit base current to about 0.35 ma – enough to drive TR1 into saturation, but also stretching the discharge time of C1 to about three seconds.

Note that 64 counts is about one minute. If not cancelled, the buzzer will sound for 64 blinks. The next 64 stay silent. When the turn signal is cancelled and left off for four seconds, the count will begin again.

Sounds like a job for an Arduino Pro Mini and a few discrete parts.

First you need to convert the on-off 12V turn-signal levels from the lamps or LEDs to 5V logic levels. You can find level-shift circuits via a Google search. Then you’ll have two sets of pulses, one from the left signal and one from the right signal. Run the 5V logic signals to two inputs on the Arduino Pro Mini.

Second you need a control program that determines what to do with these pulses and when to turn on an indicator (visual or audible). When the software detects a pulse on either input it starts two timers, Timer1 for 2 minutes and another (Timer 2) for about 1.5 times the length of a turn-signal on-off period (1.5 times the flash duty cycle). Each incoming pulse restarts Timer2. So as long as the Arduino Pro Mini receives turn-signal pulses, Timer2 continues to run. If at the end of the 2-minute period Timer2 is still running, the indicator turns on. The indicator turns off as soon as Timer2 stops running. That indicates no more pulses from the turn signal.

As an alternate, an Arduino Pro Mini could simply count the number of pulses that occur for your vehicle in a 2-minute period and when the count equals that number, it turns the indicator on. You might include a “kill” switch for the indicator in case you need to keep the emergency flasher on for more than 2 minutes. For more information about the Arduino Pro Mini, visit: https://www.sparkfun.com/products/11113.

I have been collecting Marklin trains since 1962. I believe, what you are looking for is the 16-20VAC transformer Marklin used to require. The basic power pack was a variable voltave, 0-16VAC approximately, transformer. It had a lever to rotate which increased/decreased the voltage output.

To reverse the engine, the hadle was pushed down momentarily, which would send 20VAC to the engine, which toggled a latching relay in the engine to reverse the ‘brushed, AC motor.’ Were I, and I might in the future, to design a solid state replacement, I would select a PIC24F or PIC33F series processor and have it geneterate a PWM sign wave. There are app notes at the Microchip website specifically regarding the digital generation of sine waves. Then you can vary the frequency for speed control, rather than the voltage, which would give much better low speed response for the engine.

Boy are you lucky!!! I started collecting Marklin HO scale back in 1962, so a 1959 vintage should be fabulous.

The old equipment had AC motors in them, and the original transformers ran 16VAC to 20VAC. In other words, they were variacs which controlled the speed by changing the voltage to the tracks. This did pretty well, except at the very lowest speeds.

So, there are a number of ways to control the locomotive. The easiest would be to use a transformer output through a potentiometer, driving a 30 or 40 watt amplifier, (direct coupled). This output would directly couple to the track. The center spikes are the Hot, with the rails being the neutral.

A more complicated, (but fun way depending on your skill level), would be to use a PIC microprocessor to PWM a sine wave to directly drive the center rail of the track. Then you would have the most control.

This is a MINOR manufacturing defect, easily repaired! Turn the unit over, so the USB connector is on the bottom, and facing left. That "large" IC on the left is the USB controller. Solder pins 25 and 26 together, and your problem will be solved. One of those pins is ground. The other is a "test" pin that is SUPPOSED TO BE grounded, but isn't. Once grounded, the chip works correctly. I did this with a board I bought from MPJA, and it solved my problem instantly.

Some of the cheaper Uno and Nano board spinoffs (among other off shore versions) use the CH340G series USB serial interface chip rather than the FTDI USB chip. All that is necessary is to download the CH341 driver and install it in your Windows/Mac system. You can get the driver from Driverzone.com or Google search “ch341ser.zip”. Just make sure your comm port settings in the software match the USB driver in Windows. You can leave both drivers in Windows without uninstalling the other.

On the bottom of the Nano board, are a few chips. One of them is much larger than the rest. That is the USB chip. You need to create a solder bridge between pins 25 and 26. One of those pins is GROUND and the other is a manufacturer’s TEST input... which they left floating. It needs to be grounded. Once you solder those pins together, your Nano will work. I’ve done this fix twice, now, and it solved my issues 100%.

The soft or “warm” sound of tubes relates to four properties.

1. Rolled off frequency response of the amplifier related to the inductance of the output transformers.
2. Slower transient response again due to the high inductance in the output transformers.
3. Soft clipping for very large amplitude signals due to the transfer characteristics related to the amplifier tubes.
4. Magnetic hysteresis in the transformer itself which alters the output signal of the tubes.

Transistor amplifiers have much higher slew rates, higher frequency response, and hard clipping when the large signals cause the output transistors to hit the rail voltage of the power supply.

Solid state amplifiers are directly coupled to the speaker load, have a very high damping factor due to the negative feedback, and therefore produce much more accurate output than a tube type, amp. This is the reason for the harsher sound which is really more accurate than the output from a tube amplifier.

If you compare the FFT (Fast Fourier Transform) frequency domain traces of the two types of amplifiers, the differences will become readily apparent. A solid state amp will have many more harmonic components than a tube amp. The direct coupling of the solid state amp to the speaker, also eliminates the hysteresis from the transformer core.

The lowest distortion figures will always be obtained from a solid state amp, in the less than .1% range. Tube amps, conversely are in the 1% to 5% range depending on their design.

Your looking in the wrong place: Maybe not definitive, but look here: https://en.wikipedia.org/wiki/Tube_sound. Even harmonics are more pleasant to the ear.

Yes, there are technical differences. Both tubes and transistors are nonlinear devices, and the transfer curve for each is unique. The transfer curve defines how the output should respond to the input. Within a narrowly defined range of input values, the output values change in “mostly” linear fashion — in math terms we would say the function is monotonic. When your input values start to go beyond the linear operating region the output is no longer a simple (linear or monotonic) function of the input.

Every device, triode, pentode, JFET, MOSFET, BJT has a unique transfer curve. Imagine that the transfer curve for a triode is not a straight line, but more of a “lazy-S” shape — the middle section is pretty close to straight, but the top and bottom of the curve rolls over. As mentioned above this curve “maps” your input signal to the output signal; any given value of input is a point on the curve that defines the output. But when the signal is near the very top of the curve, the output signal change for a given change of input is diminished (like a demon turning down your volume knob). This results in a soft clipping effect if the top of the transfer curve is relatively smooth. Gentle excursions into nonlinear behavior in a triode tends to produce a nice mix of even and odd harmonics; and, if I recall correctly even harmonics lend warmth to the sound.

In the case of a BJT (bipolar junction transistor), the “lazy-S” curve looks more like a “Z” drawn backwards, where the extremes of the transfer curve don’t bend gently. Instead, they have sharp “corners” and tend toward a “flatter” transfer function at the extremes. When the input signal gets into this nonlinear region a large change of input signal results in almost no change of output signal, but can produce lots of harmonics — predominantly odd-harmonics.

The clipping is more aggressive at the extremes of signal input; almost an “all or nothing” affair. Contrast that to the tube clipping, which is more like “diminishing returns.” I have heard of an amplifier circuit that adds even-harmonic components of the signal. I haven’t built it, but the idea is that it would create a warmer sound.

Having said all that, clipping and harmonic content (warm versus cool) should not be thought of as synonymous. Clipping occurs at the extreme limits of signal input. Nonlinear transfer curves can create harmonics at any value of input signal. When you look in the mirror in the morning, you are seeing a “linear” reflection of yourself. At the carnival or fairground when you stand in front of curved mirrors that distort your reflection, you are seeing an exaggerated “nonlinear” reflection of yourself. While seeing such exaggerated nonlinearity is humorous, in the audio realm it would be intolerable to listen to... maybe.

Guitar effects pedals intentionally distort the signal, sometimes to an extreme that is almost unrecognizable  — but, that’s an article for another day.

The answer is simple, really. Tubes don’t so much clip, as go soft, rounding the peaks off the waveform. Solid state, however, works all the way up until it hits the head; at which point it cuts it off sharply. The resulting distortion can be either modeled as odd harmonics for solid state, or even harmonics for tube amps. And it’s all in how they are perceived by the ear; the softer clipping that tube amps do causes it to be more perceived as being not quite as loud, whereas the hard clip of solid state tends to be rougher sounding. And to conclude - if your system routinely clips, you need to Tim Allen (MORE POWER!) it.

In this case, all clipping isn't the same. A transistor circuit is fine up to the power supply voltage, where it mows the peaks off square and flat. This produces a harsh distortion similar to the fuzz pedal for a guitar. A tube circuit starts to round off the peaks before they actually run into the power supply voltage. The rounder peaks account for the "warmer" sound.

It's not about clipping. Tubes and FETs have greater inherent 2nd harmonic distortion which gives them the warm sound. Look up the books and articles by Douglas Self to truly understand why modern bipolar output amplifiers are very hard to beat for sonic clarity. Some of the new Class D amplifiers (TI, others) are quite amazingly clear, too. I still use FET input op amps (LF412) when I want some of that tube warmth. But when I need absolute clarity, modern bipolar devices (LM833 and newer) for crossovers, and bipolar output stages, are (in my opinion) best. Read what Self has to say.

It has to do with the type of distortion between the two architectures. Tubes tend to have more odd-order harmonic (3rd, 5th, etc.) distortion; solid-state amps are relatively distortion-free, and any distortion they have is generally with even-order harmonic (2nd, 4th, etc.) distortion usually generated by their feedback circuitry. With clever signal filtering schemes, solid-state amps can mimic the warmth, etc. of tube amplifiers, without the power-wasting (i.e., heat) that tube amps have.

Simple answer: To the first order, they are pretty similar, however, typically tube circuits are operating at a much higher voltage — a transistor circuit operating at lower voltage, will tend to have higher harmonic distortion than a tube operating at a higher voltage. If you use a high voltage transistor then you can get harmonic distortion from a transistor which is comparable to (or better than) a tube, but you usually have a higher noise floor.