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Recent Questions

March 2018

Chasing Lights

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

Hitec Servo Question

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

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

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

February 2018

Legacy Printer Port (LPT1)

I’m doing some work with legacy computer equipment and have written Basic software to control time and temperature in a high temperature kiln. I’ve used an old Compaq laptop (LTE Elite 4/40CX). I use the COM 1 port to control temperature and the LPT1 port to cycle the kiln on/off via an SCR.

Everything works great. I’m able to toggle the printer port pins via OUT commands. When trying other legacy computers, everything works except the printer ports don't respond to the OUT commands and remain in a high state. However, they DO operate the dot matrix printer indicating they are functional. My question is how do I gain control of some of the data pins and be able to toggle them high and low?

Jerry Sobel, R.Ph.
Las Vegas, NV

Amplifying Plant Signals

I’m trying to duplicate an ESP experiment described in the book “What A Plant Knows,“ by Chamovitz. Basically, I need an amplifier and sensor to read signals from stems and roots. What frequency response does the amp need? My guess is from DC to maybe 20 Hz? If this is the case, then what sort of amp configuration do I need?

Carlos Dixon
Flint, MI

Measuring Breathing Rate

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

Neutralizing Battery Corrosion

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

January 2018

Converting S-Video to Composite Video

I have a newer HD LED television that does NOT have an S-Video input jack! My old VCR and tapes are all S-VHS, so I need a schematic for building a converter for S-Video to Composite if I want to watch my old family movies. Please help!

Henry Vaden
Whitestone, NY

Chip Replacement

I have an old guitar “echo” pedal that is dead. After some troubleshooting, it appears the SAD1024 chip in the unit has given up the ghost and I have been unable to find a replacement chip.

Is there a substitute for it or a source for replacing it?

Mike Styles
Pennsauken, NJ

Low-Cost 3D Printers

I’ve been eyeing 3D printers for a while, and there are now basic units in the $100 range.

However, it appears that software can cost between free and several hundred dollars depending on features and capabilities. I like free. Is anyone using free software to create and print using one of these low-cost printers? If so, which software and printer are you using that you would recommend? Any caveats?

Brenda Spellman
Green Bay, WI

More Questions