2020-04-13 Beeping -- --- .-. ... . loud enough (2) 6 months ago
Today I had time to work on the transistor switching to make the morse oscillator work. As I noticed before the Kent Morse practise oscillator kit is powered directly via the key which draws more current than the nanokeyer I built can handle. So I had to calculate a transistor switch. That's something I learned a long time ago when I did electronics trade school from 1985 to 1989. In Dutch: MTS electronica. That knowledge had to be dug up again when I did the advanced radio amateur course but since I didn't have to use that knowledge it all sunk away. But, google to the rescue and I found lots of examples, but the easiest one was at Transistor as a Switch - ElectronicsTutorials which explained exactly what I wanted. The next item was 'which transistor'. The default NPN transistor is the BC547B, but the theoretical current through the oscillator is a bit more than this transistor can handle. But a fellow amateur had a few BC337 transistors spare in his junkbox, so I could continue with this project. Today I did the drawing and the calculations. I looked up the specifications for the BC337 in full saturation, at which time the Vbe is 1.2 Volt, Vce is 0.7 volt and Ibase is 1 milliAmpere. So I ended up with a resistor of 6800 Ohm at the input (which is (9 Volt - 1.2 Volt)/1 millAmpere rounded) and after building it on a breadboard it went beep with an input current of somewhat over 1.0 milliAmpere. Update: Second test was with the nanokeyer, which first gave no sound, but that was due to me turning the volume down on the practise oscillator. Turning it back up fixed the problem, and I now have loud morse! In the end this is giving me a good feeling. I had a kind of problem I haven't had to solve in ages so I had to relearn how to solve this, I found the solution method and was able to apply it in theory, practice followed the theory and it all worked as designed.