I'm looking to build an add-on to my Geiger counter once I get it all fixed and ready to go.
Basically will consist of the Noritake VFD, an AVR, a LED and a speaker / headphone jack.
A tick on the Geiger counter generates a -25V spike at a very low current at the Amphenol 75-PC-1M headphone connector.
It was really only ever designed to use the headphones that came with it which had an impedance of 4K Ohm and inductance of around 600 to 700 uH.
If you put a 8 or 16 Ohm speaker on it, the tick is barely audible because the current draw is more than it was designed for.
There is a Geek Group video where they use an optocoupler tied to an interrupt pin on the AVR and it uses that to do counting of ticks. Would you say that would be the best way to do it? What about a transistor of some kind? I have several 2N2222 and 2N3904's in my collection.
Apparently a standard thin piezo element works well with the unamplified signal at a reasonable volume so if providing amplified output would complicate it, I can live with just a piezo.
The VFD and the AVR will need +5V and I can figure out how I'm going to do that separately. The VFD will also need 4 pins on the AVR for its own usage. If I can squeeze it down to an ATTiny45/85, then even better, but I'll have to see how big the Hex file is after I write up a program.
So for just the signaling part, do you think just a 2n2222 or 2n3904 could work?
On the NPN, if the base is higher than the emitter then electricity will flow, but -25V is not higher than +5 (or is it?)
On the PNP if the base is lower than the emitter, electricity will flow that sounds more like it except -25 is lower than +5 but also no signal which would be 0V is also lower than +5, right?
Sorry if it sounds like rambling, I'm just sort of conceptualizing it right now.