Tech Forum Questions

True, aluminum capacitors will deform with years of operation at reduced voltage (or no voltage). The typical aluminum capacitor will have a leakage current that increases with capacitance and voltage. A 40 µF 40V cap would have leakage in the order of 2 µA.

To test your capacitor, connect it through a 10K resistor to 24 volts (or 40 volts if it is available); if the voltage rises to 24 volts or more, it is okay. If not, leave it connected until the voltage does rise above 24 volts. You can use a smaller resistor to speed up the process, but don't let the cap get hotter than 50 degrees C.

Short answer... maybe.

You can often reform electrolytic capacitors by slowly ramping the voltage up, or above, your expected voltage. Keep a current meter in series and measure the charge current (after you have reached your top voltage. It should be in the microamp to low milliamp range for a good capacitor. If its higher than a milliamp or two you have a cap that is breaking down (high leakage).

Remember, low voltage electrolytic caps are pretty cheap so don't get caught by false economy.

Quickly braking an electric motor requires a circuit that will quickly dissipate quite a bit of energy. Texas Instruments has produced a paper, "The Art of Stopping a Motor," available at http://e2e.ti.com/blogs_/b/motordrivecontrol/archive/2013/10/18/the-art-of-stopping-a-motor.aspx. TI also has motor control dev kits that offer braking circuits and techniques that might help in Tsidqah's circuit. The kit documentation usually includes code and circuits. The Microchip Technology application note, AN-905, "Brushed DC Motor Fundamentals," offers a way to provide a shunt to ground that brakes a motor: http://ww1.microchip.com/downloads/en/AppNotes/00905B.pdf.

I suggest the designer replace the 4PDT relay with a MOSFET H-bridge circuit that offers more flexibility for various braking applications. Also, real time voltage and current measurements taken during braking with a load resistance should help determine the characteristics needed in a braking load and switching circuits. As for a testing load, consider a non-electronic clothes iron or a toaster oven.

If I assume that RLY1 is not connected to short out the power supply  and is shown de-energized, when RLY1 is energized, the motor connections will be reversed and the motor (acting as a generator) will try to drive the positive rail of the supply more positive. C4 will soak up some of the reverse current and when Q1 is turned on, it will limit the voltage to about 12 volts (1 ohm x 12 amps). Input to the power supply has to be turned off at this time.

There are two problems: During the transition time of RLY1 when the motor is not connected to anything, the voltage will shoot to the moon, possibly damaging the motor, and the delay time in PCB17 may not turn on Q1 in time to limit the voltage below 200 volts. One solution is to connect a 12 amp diode and series resistor across the motor to limit the voltage to 200 volts (R = 200V/12A = 16 ohms). A 75 watt light bulb would no doubt work as the resistor.

I'm not sure what you are doing with the 4PDT relay as shown, so maybe it is a drawing error. The way it is shown, the motor feed and motor are both shorted! For motor reversal you only need a 2PDT relay. If you are paralleling contacts for increased current, that's a bad idea since there is no guarantee the contacts will open or close in unison, so in effect, one contact will still carry the load. Paralleling for redundency is also not good because if a contact welds itself, bad things can happen when the parallel contact switches.

I assume since there is no logic flow provided, that the 'TRIG' signal goes low before the 'EBRK' signal goes high, and what about some protection for the input to the opto-isolator U6. Likely the spike is exceding LED PRV rating. I would think clamping diode(s) would help with the CEMF and perhaps an R/C as well. Hope this helps!

3-D printers (aka rapid prototyping machines) and laser cutters are very different animals. The laser cutter can be used to "machine" metals by laser ablation of the surfaces. A 3-D printer (such as MakerBot) uses a curable plastic powder or filament for producing layer upon layer renditions of whatever you draw on a Computer Aided Drawing (CAD) system.

Polyethylene Terephthalate (PET) filaments produce stronger products than the usual ABS plastic materials (A UT Austin student reportedly made a working pistol out of ABS but I am not sure I would want to trust my safety to the strength of plastic in this case).

The replicator (3-D printer) will run about $3,000. MakerBot also sells a digitizer for about $1,000 which allows you to reproduce an existing product by scanning it into the computer versus the laborious process of producing a 3-D CAD drawing. Using the Replicator and the Digitizer/CAD system together makes it possible to produce nearly anything you can imagine as long as it fits into the 3-D printer. I have seen a complete ball bearing set made as one piece (no assembly required) on a old 3-D printer which moved exactly like a metal bearing produced by sophisticated machining processes but the plastic did not have the strength to hold up in service. I can see using ceramic materials which can be fired to produce strength as a future wave in 3-D printing

Why not ask the city to place a mirror? In Belgium you see those on many places.

I see a couple of problems with your idea of a Traffic Detector. First of all, the "pole on the other side of the road" belongs to a utility company and they are usually pretty adamant about "devices" being installed on their poles (for years, my Father tried to wrap a pole with sheets of 16 gauge aluminum to keep squirrels out of a pecan tree and the power company had him remove the sheets pronto). If the company allows you to put up a "target" to bounce a signal from, there is still the problem of aligning the "target" such that any size vehicle would be picked up EVERY time (or your safety would be compromised by a missed vehicle). Using sonar to "bounce off a target" most likely would not work and using radar would get into issues with the FCC, plus the need for Doppler signal processing to ensure you detect only moving vehicles and not plants or stationary devices (aka very complicated digital signal processing and VERY costly).

Since you are using your hearing now to detect approaching vehicles why not use a Super Ear Listening device ($29.50 at www.amazon.com/SuperEar-Personal-Amplifier-Listening-Compliance/dp/B000X2H8G4/ref=pd_sim_hi_1/182-4508871-5045937) or the Bionic Ear and Booster set for even better results ($155.99 at  www.amazon.com/Bionic-Ear-And-Booster-Set/dp/B0012N6GZ2). Building either of these devices would require lots of electronic/construction skills (not for the novice since the SuperEar uses a highly directional microphone and the Bionic Ear uses a parabolic reflector), adjustment/alignment of the device to ensure accurate identification of approaching vehicles would be critical, and the cost of construction more than likely would equal or exceed the cost of a proven manufactured device. I am an old school electronics person and love building, but when safety is a concern it is best to use a proven device rather than a home brew.

Curtis, contact your local road department. Around here in SE KY they put up fairly large convex mirrors for just the problem you asked about.

You might want to look at using a microwave doppler sensor which you can find at DX.com searching for: Jtron HB100 10.525GHz Microwave Doppler Wireless Radar / Detector Probe Sensor. It is less than $10.

A pair could be used to detect vehicles approaching from either direction. The sensor could have a solar panel charging a battery, a low power receiver which you would trigger with a transmitter when you approach the intersection, which then would turn on the two radar transmitters, one first, then the other. If traffic is sensed the unit could flash a bright red LED, otherwise it could flash the green LED and time out after a minute or so.

There is no need to be transmitting radar signals all the time, this wastes battery power. Powering a receiver which then turns on the doppler sensors offers much less constant power draw, thereby making the power demands less challenging. For the RF link, one could hack a receiver/transmitter that is intended as a mailbox monitor or driveway monitor. Each has a receiver circuit that has modest power draw and are available for reasonable cost.

How about mounting a box with a doppler radar module (ebay search "doppler radar module") mounted on the pole across the road, in a plastic box, with an LED to indicate when the doppler detects a car? The modules cost under $10 from the far east. Biggest problem I can see is providing power. If mains power is not available you could use a solar panel and rechargeable battery. You need to check local laws regarding possible licensing of the doppler transmitter and get permission of the pole's owner.

Telescope position control is not for the faint at heart. First of all, the controller must be able to move the telescope in Azimuth (in a circle around the scope) and elevation (vertical angle from the horizon to the point above the scope - zenith) and convert these angles to the celestial equivalents of latitude and longitude called Declination and Right Ascension, respectively.

You must start with the telescope aligned with the Earth's axis of rotation which can be accomplished by sighting Polaris (the North Star). Then the telescope position controller must be able to track the object you are interested in by countering the Earth's rotational motion.

Before tackling building a positioning controller, (not an easy feat involving electronics, mechanical systems and programming) look at Celestron (www.celestron.com), Meade (www.meade.com) or Gemini (www.bisque.com/help/theskyv6/telescope/Gemini_by_Losmandy_Instruments.htm). Both companies make telescope positioners for a variety of telescope sizes and types.

Why would you use a big stepper to drive a telescope? Surely you are not considering a direct connection to the telescope's polar axis? That would produce a very jerky motion instead of the smooth motion needed for observation or photography. Therefore, you still need gears and you really need a high ratio worm gear or a series of compound gears to get a high reduction ratio. A relatively small stepper or DC motor will then work just fine.

Amateur telescope makers have used a wide variety of drive mechanisms. I have seen worm drives made by wrapping a threaded rod around a wood disk to form the "teeth". A screw with the same thread pitch can be used to drive it. If the scope is well balanced, little torque is needed to drive it. On the other hand, second hand worm wheels can often be found in places like ebay and other resellers.

Since a telescope moves at such a slow rate, some are driven by a cord or wire or strip of metal that is wrapped around a wheel instead of a gear. The cord/wire/strip is pulled by a nut that runs on a threaded rod that is turned by the motor. Since you can track from sunset to sunrise with only a half turn of the polar axis, you don't even need the full circle on that wheel. A fast mode or a nut that can be released would allow faster resetting for another observation.

Have you tried SAMS Photofact?: www.theschematicman.com - They probably had one for that radio, it's in the correct time frame. You'll need the make (RCA) and model number, perhaps even a version number on the circuit board. But, I don't know about radios, it did help when I was working on TVs.

Rider schematics were published up to 1954, too early to have included your radio which was probably made in the early 1960s. Howard W. Sams photofact service folders started in 1946 and may be still in production. I have an index which I believe I downloaded from www.servicesoftware.com in 2010. It lists 16,283 RCA schematics of radios, televisions, record players, and the like so if a schematic of your radio exists, it should be there. All you need is the model number to find it. I don't know the cost to download a schematic but it is not free.

You can also check  https://www.samswebsite.com/

Whether it's an old radio, TV, test instrument, audio gear — anything "antique", including older transistor radios, go to www.antiqueradios.com and check out their forum, especially under the section "transistor radios". This is the best source for help with antique electronics anywhere on the Internet.

All smartphones include a GPS and it would get the direction information from it, from the satellites. Try turning the GPS off to see what happens.

While I do not have an answer to your question about bringing a product to market, I know my self and others would be interested. If someone does give you the answers/help that you need would it be possible to keep a journal on the process and maybe submit an article to Nuts & Volts on how the process went for you. It may inspire others that have designs/prototypes to get theirs on the market.

Good luck in your endeavors.

In answer to your question — Yes you should learn about electronics fundamentals along with learning about microprocessors.

You need to have an understanding of the basics, however you do not need to get a degree in electrical engineering.

Your best bet is to check out your local library and see if they have any books dealing with electronics fundamentals. You may want to see if they have a copy of the ARRL Amateur Radio Handbook, they also have a book titled Understanding Basic Electronics which will help you get started. I don't know whether or not  you have your ham license but you may want to see if there is an amateur radio club in your area and get your self an "Elmer," which is ham radio talk for a mentor, as most hams that I know of are willing to pass on the knowledge they have acquired.

There are also several groups on Yahoo devoted to beginners which are worth joining.

Good luck in your endeavors.

Starting learning electronics with discrete components (resistors, capacitors, diodes, etc) or microcontrollers is a good question. Fortunately you can choose to start with either and be successful due to modern kits and the Internet. If you are "into" programming in C language, microcontrollers would be a good place to start.

To start in the microcontroller field, I would start with the BasicStamp. Parallax (www.parallax.com) has some good starter kits which supply the microcontroller, breadboard and other components to perform the experiments they have well documented in the enclosed manual. After gaining proficiency with the BasicStamp, you can move up to the Arduino (http://makerzone.mathworks.com/arduino) or Propeller (www.parallax.com). Nuts and Volts has projects every month on microcontroller type systems which can also be used to further your self-training.

If you don't feel comfortable with programming, learning the basics of electronics may be the place to start. Googling "electronics tutorials" will show you a number of FREE websites which offer electronics training for beginners. Also The Nuts and Volts Webstore sells books and kits to help you learn electronics.

Electronics is a neat field to study. It is not easy. It is not for everyone. But anyone who is looking for a challenge, electronics is the place to be. Whether you start with basic components or microcontrollers, you will eventually see the need to learn about the other field. Microcontrollers use basic electronic components to function as a system and often it is advantageous to replace a "kludge" of electronic components with a microcontroller app.