Saturday, 30 October, 2004
Code Practice Oscillator
I know the picture's not all that great, but it's about the best I can do with this little Creative PC Cam. What you're looking at is a code practice oscillator that I build from a schematic I found on the Web. The thing is incredibly simple, but I managed to have quite a bit of trouble putting it together. But I was fairly impressed, considering that it was my first electronics project. I managed to get it working without smoking any parts or burning anything important with the soldering iron.
The heart of the circuit is a 555 timer chip, that performs some kind of magic that normally would take a transistor and a few other parts. I'm still trying to understand exactly how the circuit works. My knowledge of resistors, capacitors, and the like is limited to their theory of operation. I can kind of explain what one of these little do-dads does, but I can't really say what it's good for in a circuit. I keep learning.
I like the circuit except for a couple of things. First, the sound is very high pitched. I lowered the value of the 150 K ohm resister in the circuit to lower the tone, but it didn't seem to help much. That's a minor problem, and I might try an even lower value to get the squeak out. The more annoying problem is that the thing "chirps" after it's been resting a while. That is, I'll press the key and the speaker will output a tone and then quickly transition to a higher tone. It sounds almost like the "boo-BEEP" of a video game. I think the problem is that the battery isn't a very well regulated supply. That's the theory. One of my ham radio friends suggested I install a voltage regulator chip to see if that solves the problem.
People seem to like putting these little circuits in Altoids tins. Just to be different, I gutted an old two-button mouse and mounted the thing in there. The tail consists of the two wires going out to the code key.
A code practice oscillator, by the way, is basically a box that beeps when you complete the circuit. It's used for practicing Morse Code.