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Basic electrical engineering question Answered

Although I can carve my way through data and can tell you a lot about how data is stored on various mediums, I am not the best electrical engineer, but I still do some projects for fun.

I have a project that I am working to help a friend of mine who works in a climbing wall.  They had an existing siren at the top for the kids that someone broke, and wanted to switch it out to something that they could put custom sound effects on.  I happened to think of the 9V recording module at Radio Shack (http://www.radioshack.com/product/index.jsp?productId=2102855#tabsetBasic), and proceeded to hack it to make it more usable for their needs.  I made two different parts to it: 1.  The recording module in a project box, and 2.  A momentary switch at the top of the wall to trigger the module.  I changed the microphone on the recording module to a 1/8 in jack, sent the speaker output to a better speaker (with an amp of course), added a record button to the outside of the main project box, and created a "triggering system" by soldering a separate wire to both 1 and 2 in the picture, and then shorting it whenever I want to trigger the sound.  It worked perfectly in my shop, but when I installed it, the test trigger on the ground works, but the switch on top of the wall does not work well... it only works intermittently.  The wall is 2-stories high, so figure a 22 foot run for the wire (and I don't remember what gauge wire I used... it was just something I had laying around... but figure cheap speaker wire).

My first guess was that it wasn't getting enough power from the battery, so I switched it out to a AC-DC adapter instead of the battery.  I am still having problems, so I am guessing it is too much resistance due to the long run?  (Would you agree or disagree?)  If so, is there some type of amplifying circuit that I could use to overcome this?  The only other explanation that I have is that the momentary switch that I am using at the top is pretty old and could be going bad, but I wanted to check first and see what you EEs out there think.

Thanks for your help!  :)

I'm sorry I am so bad at explaining this... I have uploaded my attempt at a schematic for clarification.

After installing a new switch, it did work a little better, but still not 100%; so I installed the relay, which solved the problem.  Thanks to everyone who helped!  :)



Best Answer 5 years ago

Does it work if you short out the long run of wire?

If so then the long run of wire is probably your problem.

You can fix it by using the switch up high to close a relay located in the project box to turn on the module.  You can probably find a relay at Radio Shack that will work off the same power supply as the module..

Yes, it works some of the time. I will try the relay. Thanks! :)

If it works only some of the time when you are shorting the 2 long wires at the base where they are soldered/coming out of the project box, then there is some problem with your project.
If I misunderstood your reply, then relay sounds like a good option.

Actually, I have two switches... one at the bottom and one at the top. (The one at the bottom is my test switch). The bottom works fine when it shorts the two wires, the one at the top doesn't. (I just uploaded my attempt at a schematic for clarification... sorry I'm so bad at explaining)

Thanks for your help! :)


5 years ago

Try twisting the 22'  wire to avoid destruction of your system in case
of a nearby lightning strike !!
The twisted pair is also a good way to avoid poor signal problems.

You could use the oto-iso wiring that made my light board out-live
every other appliance in a gaming hall under strike condition.


wiring.jpgOPTOISO -snap.jpg

I didn't even think of twisting the wire... thanks for reminding me! :)

What happens if you just short the wires at the top of the wall? (not pressing the button, but checking whether closing the circuit works with the long wires).

It works a little better, but not much better. I remember from when I designed it at home that it was picky when you shorted the wires, but if you used a switch it worked better. Not sure why...

I'd try a new switch before worrying about changing other stuff. A cheap microswitch should last a LONG time when mounted in something like a big cherry-button.

Thanks for the advise! I picked up a switch and relay on my way home today, so the next time I go there I will try the new switch first, and if that doesn't work I will try the relay.

Thanks again! :)

Does it work reliably at top of the wall, when you trigger it there ? Sounds to me like the wire length is the issue.

No, it doesn't work all that well at the top, but it works pretty decent at the bottom... so that was my thought process was the wire length... and it's a pretty cheap wire on top of it. :/


So the module and speaker are on top of the wall, and the PSU and switch are at the bottom ? If that's the case, you need to use a higher voltage supply and put a regulator on the top of the wall.

What you will find is that the operation of the chunky little amplifier is injecting supply noise into the circuit, as the current surges in the supply lines. Try adding some caps Like Iceng suggests first, its simplest, otherwise, if you have to remote the main supply, do what I said.

No, actually all of the electronics are at the bottom, and only a trigger is at the top. I'm sorry I am so bad at explaining this... I have uploaded my attempt at a schematic above. Thanks for your help! :)

Are you using the button from the original siren at the top of the wall? If so it may be the button has gown bad and that's why the original alarm stopped working correctly.

I am using the original button at the top... so I did think of that... if it has gone bad, would it be something visible? I did open up the box at the top to make sure it was wired correctly, and it looked OK to me (no corrosion that I could see, and the solder looked good), but it is also possible that I missed something.


The metal contact in the button could be bent out of shape preventing it from making contact and closing the circuit. If you can gain easy access to it then make sure it's making a good electrical contact when the button is pressed.

Yes, I tried that... it's making contact... that was one of the first things I thought of because I'm told that they had problems with that before.

Even if you used 100 feet of wire, it would only measure a few ohms. Since very little amperage is flowing through that wire, is another reason the wire is likely OK. I suspect the switch has corroded contacts or you have a bad connection on the wire. Measure the ohms you are getting when you push the switch. It should be very low, like 2 or 3 ohms at the most. If it is 100 or 1000 ohms, then that is the problem. Replace the switch will most likely fix it.

Great! Thanks for your help! I was thinking that might be the case, but I didn't see any visible signs of damage, so I wanted to check first. :)


5 years ago

Try some 470 uF capacitors at the electronics power attach point if the battery or dc supply is 22 feet away.

It's actually only about 5 feet... all of the electronics are at the bottom except for the one trigger which is about 22 feet away. Would the caps still be a good idea, or is it unnecessary at that distance? I'm sorry I am so bad at explaining this... I uploaded my attempt at a schematic above. Thanks for your help! :)