[sdiy] frequency counter

[Magnus Danielson]

Antti Huovilainen wrote:
> On Sun, 25 Oct 2009, David G. Dixon wrote:
> 
>>> (I'm gonna make an AVR one right now just for fun.  Thanks for the
>>> inspiration.)
>>
>> Yes, I think this one will have to wait until I learn microprocessors.
>> However, I'm pretty old, so it might take a while...
> 
> Frequency counter is going to be pretty damn simple as far as the 
> programming goes. It can be done in pure C. Just program the timer and 
> capture ports for period measurement, wait for interrupt or capture 
> finish, read value, output to display, loop to beginning. Not a bad 
> starting project IMO.

I agree. A simple frequency counter setup should be a nice exercise with 
just a little of low-level programming, post-processing, control input 
and result output.

Just make sure that a crystal oscillator is used to get some accuracy 
and stability. Internal RC oscillators can vary alot.

One very useful interface feature is to have a pot for setting the 
measurement time. That way can update speed be traded for resolution 
with a very simple and effective user interface. I miss it on more 
modern counters. There is usually an 8 bit A/D lying around idling, so 
it will be simple enought. The ADC value needs to go through something 
like an exponentiation such that it spans several decades just like a 
coarse tuning pot. I think that would be most useful.

Cheers,
Magnus