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Recent Questions

April 2017


Ni-Metal Hydride Battery Chargers

Now that Ni-Cad batteries are becoming an endangered species, is there any way to convert their chargers to work on the newer and ecologically sounder Ni-Metal Hydride batteries? I read that the Ni-Metal batteries have very different charging requirements rather than the constant current chargers for Ni-Cads. I have several bench chargers, not to mention a multitude of “wall warts” that I would like to modify.

#4171
Michael Herman
La Quinta, CA


POTS Ring Generator

I need a circuit to generate 20 Hz 90 VAC to ring a POTS telephone on a theater stage. That’s Plain Old Telephone System vs. Pretty Advanced New Stuff (PANS) for the younger readers. If I could locate an old crank ring generator, it would work but would not be as convenient.

#4172
Dale Carlsen
Woodbridge, VA


Warm Cows Are Happy Cows

My daughter is in 4H and has a calf we are raising in a shed behind the house. Recently, the bulb burned out on the heat lamp we leave on to keep the cow warm. Is there a simple circuit I could use to remotely monitor the temperature and alert me if it drops below a set point? I know there are remote temperature gauges but I need one with an alert or a way to hack one to add an alert. Any ideas welcome.

#4173
Robert Lowery
Florence, SD


March 2017


Getting Started With High Voltage

I would like to experiment with high voltage projects, but all my experience in building power supplies is for low voltage (typically 5 or 12 volts). I’d love a schematic for a high voltage power supply that could produce between 0 and 250 volts safely. Also, any safety pointers for getting started would be appreciated.

#3171
Ed Warren
Everett, WA


Reliable Voltage Source

I am designing a battery powered circuit that requires a very reliable voltage source. I was considering using a zener diode in series with a resistor across the power source and then tapping it at the diode/resistor for the power point, but it seems this would be very wasteful for the battery. Would I be better off with a linear regulator like an LM317 and if so, would it create as accurate a voltage?

#3172
Gilbert Kreps
Midland, TX


Laser Flashing

I need help with a circuit design to flash a 10W laser diode at 14 Hz. A crystal controlled 555 IC is too variable due to temperature, and must be calibrated. No microcontrollers please; too complex and require coding. I need a simple discrete design.

The problem is laser diodes are pulsed with a tiny duty cycle, so they must be pulsed at high PRF to create the 1/28 second ON cycle. Probably 100 kHz for 1/28 second, off for 1/28 second, repeat ... It may require multiple laser diodes, interleaved ON pulses to smooth out the 14 Hz ON cycle. I basically want to emulate as close as possible the 14 Hz square wave. To top it off, this needs to run off the “dirty” rectified 6-12 VDC from a motorcycle alternator.

As an alternative, instead of laser diodes, an array of LEDs, perhaps 6 x 6 (36 LEDs) may be acceptable to simplify down to just a 14 Hz crystal controlled strobe timer.

The whole thing needs to fit in a garage door opener sized box.

#3173
Tom Uryga
Hillsboro, OR


Surround Sound Questions

I recently upgraded from an older two-channel stereo system to a 5.1 surround sound receiver. I have left, right, center, and sub woofer speakers set up at the front of the room, but no easy way to run wire for the rear speakers.

What’s the best DIY wireless method to get my surround sound to the back of the room?

Does someone have a schematic for a stereo transmitter/receiver that I could build? Would using a combination wired and wireless setup  have any issues with syncing the front and rear channels?

#3174
Dustin Quintanilla
San Luis Obispo, CA


February 2017


Auto Bell Galloping Dominoes

I have an electro-mechanical gambling machine — Galloping Dominoes — from the company Auto Bell, and would greatly appreciate if someone could direct me to where I could find a schematic. It has a motor that turns four large switch cams and three smaller cams, and has numerous multi-pole relays all interconnected. Thanks!

#2171
Randy Grunwell
Suwanee, GA


Radio Whine

I have been using a Sony ICF-9740 AM/FM table radio on my nightstand since 1974. Recently, there is increasing interference on the AM band. It’s not AC “buzz” or “hum” that one would expect from old power supply filter caps; it's more of a high frequency whine — my guess is around 6-8kcs, and it's consistent even when the volume is turned all the way down. I could replace this unit but I would really rather fix it. Any pointers on finding the source of the noise or theories on what might be causing it?

#2172
Radio Whine
Houston, TX


Three-Way LED Flasher

I need a simple circuit to sequentially flash three separate strings of 10 LED lights. Flashing two strings is easy; three is tougher.

#2173
Michael Herman
La Quinta, CA


More Questions