Tech Forum Questions

You might try your digital camera, just turn it on so you can watch the display and point it at your IR source. Many digital cameras were able to do this until they discovered it would allow "seeing" underneath someone's clothing. If your new camera doesn't show any IR try an older camera or pick up an older one at a yard sale. Take some batteries with you & an IR LED you can test it with.

Alonso, all you need to see if IR LEDs are emitting is your humble camcorder or other CCD-based video recording device.  Simply kill ambient room illumination (lighting, close drapes, etc.), activate your IR source(s), then use your camcorder in "night mode" to see the IR illumination.

In fact, you can use this method to determine if your IR remotes are working or not - just point the remote at the camcorder lens and press a remote button.  You'll see the emitter end of the remote glowing/flashing in the camcorder's viewer if it's working.

Hope this helps.

Regarding Alonso’s question about needing to see infrared light, most digital cameras are sensitive to IR light, and it can be seen on the EV.

Most digital cameras are infrared (IR) sensitive. The simple test is to point an IR remote control at the camera and watch the LCD screen. For the "dead spots" or shadow tests, turn all visible lights off, then turn on your IR source. Look around the living room with the digital camera (I recommend lowering the screen brightness), and see where there is no illumination with the IR source.

I've found that my digital camera can see the IR LEDs and have used it for that purpose. Just point at the LED and look at the viewscreen.

There are a few options for higher performance processors that are moderately compatible with basic Arduinos. My personal favorite is the Maple from Leaflabs.com. Some others are the Arduino Due, and the ChipKIT boards from Digilent. Unfortunately, all of these boards run at 3.3V, which often means changes to external hardware are needed. The Maple and ChipKIT boards have several 5V input compatible digital pins, and 5V analog input is possible using two external resistors.

All three boards will require some modification to anything but the most basic code. The Maple will require the most changes, but also has the best access to hardware features (timers, high-speed ADC, etc) due to those changes. The Due will require the fewest changes, and has the best support for standard libraries. The Maple and Due have the best documentation. If you like the look of these boards, make sure to check that libraries you use will be supported.

If 5V is a must, you may have to consider switching development platforms. Both Atmel AVR and Microchip PIC microcontrollers are available that run at much higher speeds and have better peripheral sets while still using 5V. I'm afraid I don't know as much about the AVR line, but PIC18F, 24F, and 30F are all quite powerful controllers. If you decide to go this route, be warned that the learning curve is very steep at the start. Don't forget to compare performance by MIPS (million instructions per second), not clock speed.

Another 5V solution is to use a second Arduino! Using two board lets you do twice the work at the same speed. You can communicate between them using serial or SPI/I2C with the wire library. This can be a lot of work, but it also may be the simplest solution to some problems. You may also want to simply see if you can improve your coding abilities.

Most people underestimate what can be accomplished with a basic Arduino or microcontroller. For instance, if your code has delay()s of more than 1ms, there is probably a faster way to run the same code. Unfortunately, the Arduino libraries are not really designed for the highest performance. For example, the only interrupts that are available using the core libraries are for pin changes. Many common programming techniques to improve performance rely on timer, serial, and ADC interrupts. If your code isn't proprietary, don't be afraid to post it to the Arduino forums to ask if there is a faster way to do the same thing. If you already use the best practices, they will also be able to point you toward an upgrade that fits most closely with what you need to accomplish.

Making the move to leadless soldering is a great idea, given the health concerns of lead toxiciciy — especially if you have children in the house or your workshop. It's important to note that the rosin used as a flux in solder can be just as problematic as the lead. You can end up with an asthma-like condition if you don't work in a well-ventillated area.

Here's a nice free circuit simulator: www.falstad.com/circuit/

Linear Technology makes a nice free SPICE program for when you graduate to more advanced design methodologies.
www.linear.com/designtools/software/#LTspice

To further your education, Digilent has some nice online instruction for analog at
[url=http://www.digilentinc.com/Classroom/RealAnalog/]http://www.digilentinc.com/Classroom/RealAnalog/[/url]
[url=http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,842,1018&Prod=ANALOG-DISCOVERY]http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,842,1018&Prod=ANALOG-DISCOVERY[/url]

Also Analog Devices
[url=http://www.analog.com/en/university/topic.html]http://www.analog.com/en/university/topic.html[/url].

For digital try [url=http://www.digilentinc.com/classroom/realdigital/]http://www.digilentinc.com/classroom/realdigital/[/url]
[url=http://www.digilentinc.com/classroom/Electronics101/index.cfm]http://www.digilentinc.com/classroom/Electronics101/index.cfm[/url].

As a side note, as to textbooks, I'm impressed by [url=http://www.ntspress.com/publications/circuits-second-edition/]http://www.ntspress.com/publications/circuits-second-edition/[/url]. Unfortunately, it’s a bit spendy.

Here’s a site on basic car audio electronics which is very engaging: [url=http://www.bcae1.com/]http://www.bcae1.com/[/url]. This one is geared towards the car audio enthusiast who wants to learn about and repair his equipment: [url=http://www.bcae1.com/repairbasicsforbcae1/repairbasics.htm]http://www.bcae1.com/repairbasicsforbcae1/repairbasics.htm[/url].

You ask how to get "a positive and a negative part of a sine wave from a circuit that runs on a nine volt battery." It is not clear how you are going to use that output, so I'll presume this is to satisfy your curiosity (or perhaps to help on your homework). The circuit suggested is not efficient, and would not make a good power supply.

First, a 9-volt battery produces direct current, DC, with a steady amplitude of 9 volts (gradually decreasing as it is drained). One simple circuit that produces a fair approximation of a sine wave from DC is a phase shift oscillator, shown below on the left side, (adapted from [url=http://www.learnabout-electronics.org]http://www.learnabout-electronics.org[/url]). The sine wave can be observed between the Out and the 0V test-points.

Second, the sine wave must be separated into positive- and negative-going signals, which is done by the half-wave bridge rectifier. The two half-sine waves can be observed between the + or - test-points and the 0V test-point. The waveforms are shown below, (adapted from [url=http://macao.communications.museum]http://macao.communications.museum[/url]). The negative half-wave should look like the second graph flipped upside-down.
 

If this did not answer your question, you might provide some more information as to how the signals would be used.

First off, neither a capacitor or inductor is added to an antenna in order to change the length, they are added to match an impedance mismatch. In effect, this is LIKE changing the length IF changing the length would match the impedance of the antenna to that of the radio & feed-line. What you are really doing is counter acting the mismatch with the equal and opposite type impedance to make an impedance matching circuit, or a fixed antenna tuner, so-to-speak.

Many terms used by hams are misleading in that they really don't do what the term is saying they do. An antenna tuner doesn't tune the antenna, it transforms a complex reactance of the feed line and antenna into a resistance so that the radio can pass all its power to the antenna. The word "complex" is used because a mismatched antenna will look like a resistor and either a capacitor or an inductor. The radio wants to "see" just a simple resistor, a perfectly matched antenna to the impedance of the radio's antenna port.

All these terms may have come into being because someone somewhere along the line said, "Oh that's like changing the length of my dipole to match the impedance of my radio" and so the idea of "changing the length" stuck. I don't know how the term came about but it creates the idea that we're changing the length when we're really matching the over-all antenna and circuit resistance to that of the radio, and that's what we're after, a matched circuit so we can put all our radio energy onto the antenna and into the air.

Try reading, An Approach To Antenna Tuning by Lloyd Butler VK5BR, it explains this in more detail: http://users.tpg.com.au/users/ldbutler/Approach_Ant_Tuning.htm

An antenna becomes resonant when the energy that is racing down the wire hits the open end and is reflected back to the sending end and the transit time is equal to the time of one cycle of frequency. The open end has high voltage and low current (there can’t be any current at the open end) and the sending end has high current and low voltage. Adding inductance at the sending end will lower the resonant frequency thus making the wire appear longer. Adding capacitance to the open end will also reduce the resonant frequency. Since radiation occurs from the wire, adding these L and C elements will reduce the antenna efficiency because it is shorter than it would be if the L or C were not added.

Capacitors...there are MANY types, physical size/confirguration, chemistry, range and ratings. Choosing capacitor types depends on many variables. Size constraints, environment (i.e. voltage, temperature and frequency).  Most capacitor applications are either in AC circuits or used as timing circuits and storage. Application of the types depends a lot on cost also. Tantalums are more effective in some cicuits due to size and tight tolerance, but are also much more expensive over electrolytics. In RF circuits, typical types are mica, ceramic, glass, vacuum, air and even oil dialectrics. (there are 100s of them) Each application again depends on cost considerations, size and power levels.

I suggest if the reader wants more data on capacitors to consult one of many texts covering the theory and application of capacitors. A good start would be -Electronic Communications- by Robert Shrader (McGraw-Hill)

I 'think' Nuts & Volts did a series on capacitors many months ago that was good reference material.

There are many types of capacitors in common uses today, with many different properties. The key difference is the dielectric, or insulating material, between two metal plates. Here are some common types. All values shown are just rough approximations. Maximum capacity is expressed as nF (nanofarad), (µF) microfarad and F (Farad), maximum voltage as V (volt) or kV (kilovolt), and maximum frequency as Hz, (Hertz), kHz (kiklohertz) or MHz (megahertz).

   Air variable capacitor: used in radio receivers and low-power transmitters. Value may be changed, but bulky for capacity. Max. ~1 nF, ~1,000 V, ~100 MHz
   Vacuum variable capacitor: used in high-power transmitters. Value may be changed, but bulky for capacity. Max. ~1 nF, ~10,000 V, ~1,000 MHz
   Mica capacitor: used in receivers and transmitters. Value is stable. Max. ~1 nF, ~1,000 V, ~1,000 MHz
   Ceramic capacitor: used in digital electronics, receivers and transmitters. Value is less stable than mica, but more compact. Max. ~1 µF, ~1,000 V, ~1,000 MHz
   Al or Ta electrolytic capacitor: used in audio-frequency and power supplies. Al is cheap, Ta more efficient. All require a DC offset and are destroyed by true AC or reverse voltage. Max. ~100,000 µF, ~300 V, ~30,000 Hz
   Ultracapacitor: double-layer dielectric capacitors for power supplies and power backup. It offers very high capacity, and might eventually approach that of electrochemical cells, but has low voltage per capacitor, so are usually placed in series. Max. ~100 F, ~1 V. ~100 Hz

Other dielectrics are used, such as paper, plastics, glass and water (yes, pure water has a high dielectric constant, low conductivity and is environmentally friendly):
[url=http://www.rle.mit.edu/cehv/documents/34-Phy.Tech..pdf]http://www.rle.mit.edu/cehv/documents/34-Phy.Tech..pdf[/url]

Ceramic caps are small, low loss, low leakage and inexpensive but the temperature coefficient varies from COG (very stable, 2% is available) to X7R (moderately stable, 10% is available) to Z5U (typically +20%, -80% over temperature). There is another type of ceramic called porcelain that is used in microwave applications; ordinary ceramics are too lossy at those frequencies.

Aluminum Electrolytics are widely used because they are low cost and smaller than a film capacitor. Electrolytic caps are leaky (measured in microamps), have internal resistance that may be significant in some applications, and vary with temperature (+- 20% typically) and frequency (not useful at high frequency). After 6 or more months on the shelf, aluminum electrolytic caps should be re-formed to regain their voltage rating.

Tantalum caps are also an electrolytic but smaller than aluminum, lower leakage, better temperature coefficient and operate at higher temperature. Cost is more than aluminum but does not de-form (loose its voltage rating) with non use.

There are other capacitor types to consider: mica, polypropylene, metalized polyester,  polystyrene, and paper. Each has pluses and minuses to consider.

Multimeters, particularly digital VOM's, and some high impedance analog types, have a Diode test postion on their scale selector. This position presets the full scale range, typically 1000 - 2000 ohms FS, to measure the front to back ratio of a diode and also the forward resistance.  Many DVM's do not provide enough voltage (up to 3 volts) in their 'normal' resistance/ohm scales to cause a forward 'breakdown' of the junction to measure it. (Especially in auto-ranging units). Also, this pre-set range allows one to test diodes rapidly without waiting for the unit to count down.

The diode setting measures the forward drop of a diode at a current of a few milliamperes. To ensure the diode is conducting, the potential across the meter probes is a few volts. On my aged Radio Shack DVM, the open-circuit potential is 2.88 volts, sufficient to "turn on" most diodes, including red, yellow and green LED's, which glow dimly. Note that blue, ultraviolet and white LED's, as well as Darlington transistors and some high-voltage diodes (that are, internally, series-connected diodes) show as open circuits, since they need a higher voltage to conduct.

The resistance setting is intended not to "turn on" a diode, so, on that setting, the voltage across the meter probes is only a few tenths of a volt. That allows accurate measurement of a resistor in parallel with a diode or across other semiconductor device, except perhaps Schottky diodes, which may have a forward voltage drop of 0.2 volts.

See [url=http://en.wikipedia.org/wiki/Diode]http://en.wikipedia.org/wiki/Diode[/url] for more information, but the list below is a rough guide to forward voltage drop at a few mA:

• Ge Schottky diode:   0.2 V
• Ge signal diode:        0.3 V
• Si rectifier:                0.6 V
• SiC Schottky diode:   0.6 V
• SiC junction diode:    0.6 V
• Red GaAsP LED:      1.3 V
• Blue InGaN LED        3.0 V

Using the diode setting, you can usually identify the type of a diode or junction transistor, as well as determining if it's open or shorted.

BTW, thanks for asking that question, which inspired me to check the open-circuit voltage and current draw of my DVM diode and resistance settings. Now my measurements should be a bit more meaningful.

The diode selection on a multimeter is for continuity and diode checking. Digital multimeters do not produce enough voltage to forward bias a diode ordinarily so this position outputs several volts at low current and sounds a buzzer if current is drawn. If the diode is good, the forward voltage will be displayed in one polarity and open circuit will be indicated in the other.

The "diode" range on digital multimeters is used to "measure" diodes (any type) to see if they are good or not. To use the range, connect the BLACK meter lead to the diode wire with the "stripe" on the diode body (cathode lead) and the RED meter lead to the other diode wire (anode lead). The following are "typical good" forward-bias readings for various diodes:

• "Silicon" diodes: "0.6-0.7"
• "Germanium" diodes: "0.3-0.4"
• "Tunnel" and "Schottky" diodes: "0.2-0.3"
• Zener diodes: similar to silicon diodes
• "Selenium" rectifier: "0.9-1.2" (approx)
• "Power" (i.e., 10A rating) and "high-voltage" (i.e., kilovolt rating) diodes: "0.7-0.8"
• LEDs: "1.6-1.8"

Reverse the leads (reverse-biasing) will show "OL" - any "numerical" reading usually indicates the diode is "shorted" in reverse-bias. This range is also useful for checking the "polarity" of BIPOLAR (PNP, NPN) transistors, if you don't know what kind you have:

• The emitter-base drop will read "0.5-0.6"
• The collector-base drop will read "0.7-0.8"
• The collector-emitter junction will read "OL" ("anything less" indicates a blown transistor)
• Reverse-bias the emitter-base and collector-base junctions and you'll read "OL" ("anything less" indicates a blown transistor)

NOTE: The BLACK lead will tell you which lead(s) are the "N" lead(s) for determining "PNP" or "NPN" polarity (use the voltage drop difference to  determine collector from emitter). It's also useful for determining the polarity of "unmarked" diodes: BLACK is cathode ("stripe") and RED is ANODE. DO NOT use this range to measure FET (field-effect transistors) as modern FETs are "static-sensitive" devices and will be probably be destroyed from the action of taking the reading. SCRs, triacs (i.e.,"thyristors") and similar "exotic" junction-type devices cannot be accurately "tested" on this range. Finally, you can measure LOW-VALUE resistors (<2000 ohms) and the range usually has a "buzzer" associated with it for audible continuity readings (i.e., wire tracing, testing fuses).

The diode function on a digital multimeter is part of the Ohms function. This function doesn't autorange. It provides a constant current to forward bias the diode under test and displays the voltage drop. You should measure about .5 to .6 volts for a standard silicon diode. Other junctions will read higher or lower depending on the construction of the device.

Yes, they have likely been damaged, I had to look up what "equalizing" a battery was since I wasn't sure. Equalizing may help but I doubt that full capacity will be restored, or if it is, it will last very long. I'm going to assume that these batteries are the deep discharge type and so you may be able to restore them at least partially.

I've noticed with my backup 12 Volt deep discharge 70 - 80 AHr batteries for amateur radio & emergency use that once I let them get even partially dry I can never get them back up to full capacity. On the other hand, I do not own a charger that can perform the equalization charge either. So, I'd say since it likely won't hurt, give it a try.

My question is: Since you never run them down, you have no way to compare to see if this has improved anything, and also, since you never run them down, why worry about it? You never seem to need whatever the full capacity is anyway.

You may contact me if you like. I'm interested since I've done battery work both professionally at Marsh McBirney, Inc., and  Gardner Labs, as well as in my amateur radio hobby.

I have heard that If you let car batteries completely discharge, they will lose one-third of their capacity.

Your son should consider the local community college, and look at other careers related to electronics. While engineers are often mentioned, technicians with with associate's degrees are now more in demand (USA TODAY).

Electronics is just one option - also consider other related fields such as  machine tool technology, industrial electronics, instrumentation repair, or machine maintenance. These programs include electronics along with motor control, programmable logic controllers, instrumentation, fluid power, sensors, pumps, valves, process control, and industrial robotics. These people are in demand and command high incomes.

For info on career options and certifications, check out the Electronics Technicians Association, International - [url=http://www.eta-i.org/]http://www.eta-i.org/[/url]

Your son needs basic skills in practical math and physics. With those, he can look at many technical-education programs, from vo-tech to an advanced degree. I recommend a visit to a nearby technical school and to an engineering department at a college or university. After your son sees what students and professors do, he should have a better idea of what preparation for a technical career entails. But don't force him into a technical field. No matter what your son wants to study, he'll need a life-long interest in learning and reading.

Technical careers can vary far and wide, and many of them do almost require a degree of some kind. If he/she is interested in engineering, then a degree will be extremely helpful. An easy way to figure out whether it's necessary is to take a look at local technical job listings. Unfortunately, the degree is often very arbitrary. It's required to get hired, but most of what you learned to get the degree is useless.

I recommend trying to test out of as many classes as possible. Look into CLEP testing through College Board, as well as specific college's Credit by Exam terms. If programming is more up his/her alley, then a degree is likely very necessary to get hired. However, unless he/she can learn very well from professors, I recommend "playing" with as much code outside of college as possible. Some of the top (non-web) languages in demand are: Java, Python, C/C++, C# and Perl.

One of the few tech jobs that does not require a degree is freelance or semi-freelance web design/development. You can learn all that you need to know through free and low cost resources. You can also get a degree in web design/development, and that might help you get hired by a design house.

The absolutely required technologies to know for web are: HTML, CSS, Javascript+JQuery and SQL. SQL doesn't get you anywhere without a server-side scripting language such as PHP or Ruby on Rails. I am admittedly biased toward freelancing web design, as that is what I do.

But web design has one of the biggest markets for selling yourself in, and a lot of money can be made. It's certainly not for everyone, though. It requires that you keep up with current technology, are good with selling to people, and are willing to put some hard (but fun!) work in. Have a look at this link for learning (web and non-networked) programming: antsmagazine.com/web-development/20-amazing-places-to-learn-code-from-scratch Ignore W3Schools and anyone who says they are a good resource. codecademy.com is where I first learned HTML and CSS (then did it again in college...).

It needs to be a field that he would like to do. Get to the book store and find stuff on getting a job. Also, find out what jobs are out there. I will tell you a mistake I made — leaving a job before I had another one. Some jobs want a high grade-point average and it may take four months or more to find one. You can get a book or two from Amazon online. Getting into a co-op job should be considered, before you get your degree. You may want to consider getting a job near home.