[time-nuts] schematics of frequency counter

[Bruce Griffiths]

The CLK1 input circuit produces an output incompatiblr with the 3.3V CMOS deice it drives.A pair of pnp transistors in an otherwise similar circuit is capable of producing a 3.3V CMOS compatible output signal.
Using independent voltage dividers to bias the transistor bases is a bad idea in that resistor tolerances may lead to a dc input offset of seeeveral tens of millivolts even with 1% resistors,
Bruce 

     On Thursday, 25 December 2014 6:13 AM, Li Ang <lllaaa at gmail.com> wrote:
   

 http://www.qsl.net/bi7lnq/freqcnt_bi7lnq_v4.pdf  this is my current board.
I'm not a hardware guy, feel free to correct my mistakes. :)


http://assets.fluke.com/manuals/6690____smeng0000.pdf schematic of cnt90
aka pm6690


Happy holidays


Li Ang
_______________________________________________
time-nuts mailing list -- time-nuts at febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.