Frequency Measurement


Author Message
Volhout
Guru

Joined: 05/03/2018
Location: Netherlands
Posts: 329
Posted: 11:25am 29 Jun 2018      

In my previous post I suggested to use an internal timer clocked by the 27MHz frequency. That suggestion was premature, and incorrect (the architecture of MMbasic on the PIC does not allow that, thanks Geoff for reminding).

I have to agree with others that na external divider is the solution.
A simple solution is to use the SN74LV8154-EP
It has 2 internal 16 bit counters that can be chained to a 32 bit counter.
The output is 8 bit parallel with 4 select inputs. So you can read out all 32 bits in 4 bytes.

You only need to provide an accurate count gate (i.e. a 1msec pulse) and clear the counter before opening the count gate.

The frequency guaranteed over the wide temp range (-55...+125C) is 25Mhz, so I expect if you keep it at room temperature, it will work fine for 27MHz. It is 3.3V in so you may want to add a small amplifier before it to easily tap into oscillator circuits.

Good luck building....

Volhout



Edited by Volhout 2018-06-30
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