Re: [tlug] Pulse counter over RS232

[jep200404@example.com]

On Mon, 18 Apr 2011 03:21:44 +0900, Kalin KOZHUHAROV <me.kalin@example.com> wrote:

> As part of a DIY Geiger counter logging backend, I'd like to read
> properly formatted pulses over RS232 on my box (and later on my
> Gumstix).
> 
> Any idea/software on how to do that?

It sounds to me like you'd need some hardware to convert clicks 
to UART stuff for RS-232. One dirtbag technique would be to use 
a one-shot[1] to extend the click to a consistent length pulse. 
A 'p' would be a start bit followed by four zero bits, 
followed by three one bits, followed by stop bits. 
For 9600 bits/second, have your one-shot extend the click to 
5/9600 of a second. I.e., about 521us. More particularly, 
for each click output +3V to +25V for 521us, 
then maintain output at -3V to -25V between clicks. 

Use cat to record the data. You might want a script around it to 
kill cat periodically, count the bytes in it (wc), and log that. 

_If_ your UART can trigger interrupts by changes on handshaking 
inputs, the hardware could just be a level translator. 
Describe the electrical output of the geiger counter. 
Is the output active or passive? 
What is/are its output impedance(s)? 
What is/are its output voltage(s)? 

[1] http://doc.chipfind.ru/search.htm?t=part&s=74121&m=0
    http://doc.chipfind.ru/search.htm?t=part&s=74123&m=0
    http://doc.chipfind.ru/search.htm?t=part&s=74221&m=0