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Tech Forum Questions

Surround Sound Questions March 2017

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?

Dustin Quintanilla
San Luis Obispo, CA

Laser Flashing March 2017

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.

Tom Uryga
Hillsboro, OR

Reliable Voltage Source March 2017

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?

Gilbert Kreps
Midland, TX

Getting Started With High Voltage March 2017

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.

Ed Warren
Everett, WA

Vehicle Detector February 2017

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.

Robert Johnson
Bolton, MA

LED Compatibility? February 2017

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?

Christoffer Mortensen
Piscataway, NJ

Three-Way LED Flasher February 2017

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

Michael Herman
La Quinta, CA

Radio Whine February 2017

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?

Radio Whine
Houston, TX

Auto Bell Galloping Dominoes February 2017

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!

Randy Grunwell
Suwanee, GA

How Much Tolerance Is Enough? January 2017

When designing circuits, is there a rule of thumb for picking voltages and tolerances of components? For example, if my power source is 12 volts, is an electrolytic capacitor with a 24V rating  “better” than one with a 16V rating? What do good designers use as a margin?

Enrico Gutiérrez
Panama City, FL

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