Friday, July 25, 2008

Low cost embedable frequency counter

Frequency Counter.jpgHeard about this on the wonderful Soldersmoke blog. A flexible digital display for home home brew radios, from Doug N3ZI.

The pre-scaler is configurable to make it useful in ranges up to 50Mhz or so. It uses an Atmel ATtiny24 which comes pre-programmed. The software includes clever things like handling the IF offset.

Normally, low cost frequency counters tend to show annoying jitter in the last digit but the author has overcome this so it seems very stable in operation.

There are three versions of the kit, from $10 to $30 for the full kit. I bought the full kit and it came quickly, went together easily, and worked first time.

I'm thinking of pairing it with a Bitx20.

Thanks Doug!


I've hooked it up to an MMR40 7Mhz rig.

MMR40 counter.jpg

I needed to make a buffer amplifier to boost the local oscillator level enough for the counter. It's based on a snippet from Experimental Methods in RF Design.

rf amplifier.png

The local oscillator output is 0.27V peak to peak, after the transistor buffer it's 1V peak to peak. I used a 2N2222a that I had on hand.

The counter was set to an IF offset of -10Mhz. Doug's software lets you do this with ease using up and down buttons that accelerate if you hold them down.

There's a plastic box HB5970 that fits pretty much perfectly. It's 140 x 110 x 35mm the CPU board slides into slots and I've just used the LCD board as the front panel (a bit ugly but functional).

box content.jpg

Having boxed it all up it looks great:

front working.jpg

I had to increase the input capacitor's value in the counter to get it to be sensitive enough with my buffer to work reliably.

Anyhow, a great kit. Highly recommended.

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