Alex's Bug Listener
Alex and I were in a shop recently where he saw something called a bug listener that was a box with a magnifier and a built in microphone and amplifier. The idea is to put a bug inside and use the magnifier to look at it up close, and use earphones to listen to the sounds it makes. Alex liked it and I thought it was an easy enough project that we could do together so I suggested that we make our own. When I told him he could do the soldering he was hooked! This page describes the bug listener we put together.
First we looked around for a magnifying lens- I have a lot of that sort of junk around from things I have taken apart over the years, so we found a nice one about 2 1/2" in diameter. Then we had to figure out how to mount it on a box of some sort into which we could also build an amplifier. Then I got the brilliant idea of using LEGO! Lego can be built into any size and shape you need as long as its rectangular. When you get tired of the thing you built, it can be taken apart and reused- the ultimate in recycleability! Cutting and drilling LEGO is very easy. LEGO will be used to make boxes for many of my projects in the future.
After we decided on the type of box, we built up the circuit - Alex did most of the soldering- on a piece of perf board, then selected a switch, headphone jack, and microphone cartridge to use. The circuit uses a 9V battery for power. Once we had all the electronic hardware more or less put together, we built a couple different boxes to hold it all. In the end we decided on the design shown in the picture. The lens is the top cover that keeps the bug inside the upper part of the box. The base contains the electronics.
Three holes were drilled in a couple of the LEGO pieces to mount the power switch, the headphone jack, and the microphone cartridge. The headphone jack just screwed into its slightly under-sized hole. Hot-melt glue was dripped around the edge of the mic cartridge to lock it in place without clogging the hole on its front surface.
Here's the headphone jack and mic plate.
This is the base with the upper box removed. If you look carefully, you can see the hole for the mic cartridge in the red plate.
The amplifier uses an old BA3308 stereo preamp IC with built-in automatic level control that can maintain a nearly constant output level over about a 45 dB variation in input level. The mic cartridge is a standard electret condenser type. The single mic cartridge is connected to both amplifier channels.
Interior, wired. The partitions keep the battery and circuit board from moving around too much.
Another successful project!
Update: April 8th, 2006
Alex's bug listener is OK for picking up the audible singing of bugs but...
I attended a biology seminar at school yesterday and found out something I had never known about bugs (and I thought I was a real bug guy!): most bugs actually communicate by making the twig they are standing on vibrate! You can't hear it with your ears because it doesn't couple to the air but other bugs standing on the same twig can "hear" it just fine!
The frequency range is well within the range of human hearing, so all that is required is a way to pick up the vibrations and send them to a recorder or headphones.
The lecture was by Dr. Rex Cocroft from the U of Mo at Columbia. He's been listening to bugs for years, has published a lot of papers in scientific journals, and even had NPR do one of their "Radio Safari" programs on his work. I am now researching the parts required to make such recordings, and if I come up with an easy and cheap way to do it, you'll find it on this web site! Check back frequently!