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Tech Forum Questions

Measuring Heat With Crystal Diodes May 2018

I have a bunch of crystal diodes in my junkbox that I want to use to measure heat. I seem to remember a circuit for it some years back that I’m trying to reconstruct from memory. It’s not working very well, so I must be missing something. Anyone have a simple circuit or explanation of how it should work?

John Marion
Bend, OR

New Life For Magnets May 2018

Has anyone tried to revive permanent magnets that have weakened over time? What is the best method? Can they be made “good as new” or is it better to just replace them?

Petrina Martinec

No Wi-Fi For The Pi May 2018

How can a Raspberry Pi be made to talk to IoT devices over low power FM rather than Wi-Fi? Looking for distances under 100 ft.

Durriyah Shamoon
Eau Claire, WI

Proper Motor Selection May 2018

I need some tips on selecting motors for an art project that continously rotates five different circular platforms (10” diameter, 15 lbs) 360° in one direction, then in the reverse direction. The complete rotation of each platform should take approx 30-40 seconds (not critical). A direct drive approach would be preferred (seems simpler), but I could use a gear reduction scheme if it were more cost-effective.

Caitlin Russell
Stony Creek, VA

PS2 Emulation May 2018

My Sony CD changer has a PS2 keyboard port to enter the CD title, details, etc. Instead of typing, is there a way to emulate a PS2 interface on a PC or processor board to automate the key presses?


AVR (Automatic Voltage Regulator) for a Revolving Field, Open Protected Type Synchronous Generator March 2018

I'm looking for a circuit to homebrew an AVR for a 25 KVA (20 KW), 60 Hz, 1,800 RPM, three-phase, 240/480 volts Star with a neutral synchronous generator that is wired up as a single phase zig-zag 240/120V output.

I'm trying to help out a brother Vet who uses this generator to supply power to his off-grid site. I'm a Seabee Vet that was a CE in the Navy. I used to work on this type of generator when they used relays to control the voltage output.

I have some experience in using the PIC and the Arduino Uno/AVR microcontroller. I would appreciate any help and offer my thank you in advance. The cost of a replacement of this hybrid analog-digital voltage regulator is way beyond his means at this time.

Amos DeCarmo
Saint Cloud, FL

Hitec Servo Question March 2018

This is my first project using all digital Hitec servos. My question is: Are these new digital servos stable if I switch the input signal into the servo — between sources — while keeping power connected? I know old analog servos would have a nervous breakdown if I switched sources while the servo was under power. I know the new digital ones have a safe position. Should I program this, cut the signal from the primary source, wait for the servo to go to a safe position, then switch on source B?

Tim Yoak
Moultrie, GA

Chasing Lights March 2018

I’m trying to emulate the chasing lights that used to be popular under the awnings at the cinema. I have a chasing LED circuit that works well, but I want to turn the LEDs off slowly to leave the comet trail effect. I’ve tried putting a 2,200µF cap in parallel with each LED with limited success.

There must be a simple way to have the LEDs turn on quickly and then fade out.

Trevor Watson
via Internet

Neutralizing Battery Corrosion February 2018

What’s the best way to neutralize battery corrosion? I inherited an old, but expensive quartz watch from my grandfather and found a heavily corroded coin battery inside the watch case. I need to neutralize the corrosion without damaging the movement.

Clarence Dugan
Quitman, TX

Measuring Breathing Rate February 2018

I’m building a lie detector based on heart rate, breath rate, and galvanic skin response. I have it all figured out except for breath rate. What sort of sensor should I use to detect breath?

Jeanne Villeneuve
Vidalia, GA

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