Velleman sells a kit that you can build, advertised to be a sound indicator. “…simple sound-to-light unit for music, the hard of hearing: can be used to indicate the telephone, doorbell, barking dog. Adjustable sensitivity with potentiometer…“ We built the MK103 kit and made a video showing a product test and review.
The construction took an hour with the only tool being a soldering iron. An additional half hour was required to trouble-shoot the board since it didn’t work the first time.
I found a couple components were shorted together on the bottom side due to poor soldering by me. Another tool that would be helpful for this project is a pair of diagonal cutters, but I don’t have any, so I couldn’t cut the wires to the proper length on the bottom of the board. I also couldn’t mount the unit to the battery pack since the wires stick out too far. Some day I’ll buy some diagonal cutters and trim the wires down.
Once the unit was finished, it worked.
Click image above for video.
Jan-17-2008 Update
A family member gave me some diagonal cutters at Christmas so I came back to this circuit board, trimmed the wires off the back, and was able to mount the circuit board to the battery pack. Here is the final, completed circuit:
A few observations:
A fresh battery made the circuit more sensitive and responsive than an older battery. When I put a fresh battery in the unit, the LEDs lit up more at lower volume sounds.
The microphone was not very sensitive, even with a fresh battery. (Turning the potentiometer all the way to one side basically turned it off. Turning the potentiometer all the way to the opposite side led to the results shown in the video above.) After making this video, I gently tapped on the mic with my finger and then the LED’s lit up for even soft sounds. Some how, tapping on the mic made the circuit more responsive. But that only lasted a minute and then the circuit went back to behaving as before, requiring loud sounds to light up the LEDs.
When I put the circuit next to our phone and made the phone ring, the LEDs did not turn on. Our phone was not loud enough to trigger the LEDs. However, my kids enjoyed yelling at the circuit and watching the lights turn on.
The kit was rated “beginner” level. Since this kit requires a soldering iron, the beginner should be old enough to respect the heat of an iron so as to not get burned. My son enjoyed watching the entire build process, helped place the components into the board, and learned about electronics along the way.
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