Digital audio module - electronics expert help requested.

Classic Toy Trains Forum
1

Some years back I bought several Radio Shack digital audio modules (276-1326) to add some sound effects on various sections of my layout after reading (in another train magazine) about them. These are stand alone battery powered devices. I lengthened the playback switch leads so that they could be located on my control panel. Everything worked great with one exception…I don’t necessarily have to push the momentary contact switch to activate the module. The modules are occasionally activated by other sources. Activation occurs when I run the trains, use accessories, or even if I touch the track after walking on the carpet. I suspect that these modules are being activated by EMI and / or static discharges. They seem very sensitive. Again they are stand alone and not connected to anything else on the layout. The only thing I have tried so far is to change the playback wire leads to twisted pair thinking maybe that would help with any crosstalk or EMI. It didn’t help at all. Any of you electronic experts have any ideas? Can I add a filter somewhere, or a ground, or something to eliminate the annoying modules sounding off without pushing the playback button.

Thanks, Mike

2

You could try putting a capacitor across the switch. Try something around 0.001 microfarad. That should be large enough to eliminate static discharges and or EMI.

Bruce Baker

3

I will give that a try. Thanks for the helpful suggestion.

Mike

4

I just wanted to close the loop with you. I did try the capacitors as suggested and it worked perfectly. No more digital audio modules going off unwanted. Now if you have the time I would really like to understand why that works. I know capacitors will store a charge and assume they are storing that static or EMI before it gets to the device (audio module)?

Mike

5

The capacitor is a short circuit at high frequencies. Your EMI glitches that were causing the problem are very short duration and are composed of high frequencies summed together. The capacitor absorbs the power of the glitches and therefor reduces the voltage produced by the glitch to almost zero so it doesn’t exceed the threshold necessary to trigger your sound generators. Bruce Baker