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Recent Questions

2019 Issue-6


Ripple Voltage Monitor

I need a circuit to monitor the AC ripple voltage on a 12 volt linear power supply? A digital display would be ideal.

#06191
Brian Lambdin
Plano, TX


LED Fader

I need a simple method to slowly fade an LED from bright to dim, then to bright again in about two seconds, then keep repeating. Does anyone have a circuit that does not require an IC?

#06192
Cindi Carrillo
Lexington, KY


Transistor Confusion

What determines which type of transistor to use in a given circuit? Are they interchangeable with those of a different type that I may already have on hand?

#06193
Donald Bodine
Middleham, UK


Relay Diodes

I sometimes see a diode placed across relay contacts backwards. Can someone explain the purpose of this and when it’s necessary and when it’s not and why?

#06194
Jürgen Abend
Pleasanton, CA


2019 Issue-5


Dish Projects Wanted

I have a couple of small satellite dishes (Direct TV I think) with receivers that have been sitting in the garage for a while. I hate to throw out technology that could be repurposed. Anyone have an idea for a cool DIY project I could reuse them for?

#05191
Devin Martel
Durham, NC


Guitar Tuner

I’m trying to build an electronic guitar tuner. Is there an IC available to generate the proper tones?

#05192
Hamish Morisset
Norcross, GA


Triangle Waves

I need a circuit to generate a triangle wave from zero to five volts.

#05193
Charles A. Parham
Galveston, TX


Car Detection

I’m looking for help designing a circuit to detect cars driving up my private road. I have in mind something like the wire loop embedded in roads to sense cars at a traffic light. Can you explain the principle behind this method and how a basic DIY version might be implemented?

#05194
Ulrike Krüger
Laconia, NH


Diesel Computer Mods

There are several entities that will modify the settings on the engine control computer for a diesel Chevy pickup to increase power. I assume they are adjusting the timing curves and other parameters. Is there an adapter and software available for me to experiment with this myself?

#05195
Karel Dostál
Covina, CA


2019 Issue-4


PA system to POTS interface

I need to put the speaker-level output from a PA system on a POTS telephone line. I don’t need dialing capability, as I can connect a POTS phone to make the call, but once the call is established, I need a circuit that will:

  1. Hold the phone line open, as I’ll hang up the phone I used to make the call.
  2. Put the PA output onto the phone line, preferably with adjustable volume. I can attenuate the speaker-level PA output to line level if necessary.

If a reasonably-priced product with good sound quality (i.e., no hum, etc) is already available to do this, suggestions are welcome. I’ve found many products for recording phone conversations or putting them into a PA, but only quite expensive ones with way more features than I need that will do the simple job I want.

Thanks for any help/suggestions.

#04191
Gary Rathbun
Placerville, CA


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