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Recent Questions

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


LED Compatibility?

I replaced some outside 60W bulbs with CREE dimmable LED replacements. The lamps are  controlled and dimmed using X10 switches. When switched off, the lamps still glow at about 20% and will not shut off completely unless I use the disable feature of the switch. However, this prevents the timer from automatically controlling the lights. What causes this and is there a fix, or are LED replacements not compatible with X10?

#2174
Christoffer Mortensen
Piscataway, NJ


Vehicle Detector

Does anyone have suggestions for buying or building a vehicle detector which can be used with the Arduino? I wish to sense and count passing vehicles.

#2175
Robert Johnson
Bolton, MA


January 2017


Uno-Known Device

I’ve used the Arduino IDE with a genuine Arduino Uno board for experiments for a few months without trouble. Recently, I wanted to permanently put an Uno in a desktop project, so I purchased some budget Arduino Uno compatible boards. The budget boards seem fine, but the Arduino IDE doesn’t recognize any of them. When connected, the boards show up as an “Unknown Device.” I am using Windows 7 32-bit. Does anyone have any pointers on how to make this board work?

#1171
Michael Allison
Camden, NJ


More Questions