i don't have a frequency meter(or money to buy it) so i wonder if someone know how to build one from a multimeter (some kind of adpter).already using a software thingy but it only goes up to 22kHz and i would need something like 100khz. :wink:

 

There are frequency to voltage converter chips available. perhaps experiment with these? It won't be as accurate as the store bought meters, you have to check the chip specs. Look up google for LM 2907 or the many other listings under 'frequency to voltage converter'

 

Why don't you make a prescaler (divider).
For example if you use any TTL or CMOS 4-bit counter
(such as 7490 or 7493 or 4017 or whatever) you can get
signal divided by 10 or by 16.
Then you use your multimeter to measure frequency after
counter. If you use decade counter, all you have to do is
shift decimal point by one place. If you use binary counter
keep your calculator handy.

 

I had to do something like this. why dont you use a comparator as a zero-crossing detector, a non-retriggerable multivibrator (fixed P/W) and an RC at the output.

With increased frequency the duty will increase. Just need to turn the pulsewidth and teh RC to yr max freq range

 

The simplest possible device is plain decade counter.
You put one of them and you have 10x range. You add
one more and you have 100x range of your multimeter.
Each counter san be single chip (ca $0.40 each) with no
external components except maybe one capacitor from
+ to - and 7805 regulator in case you use TTL chips.
I would suggest two counter chips (cascaded) and SPDT
selector switch to choose range 10x or 100x.
Someone has to show me simpler and/or cheaper circuit.