I have the desire to add a frequency display for a clock generator. Certainly not necessary, I can use my DNN, but it would be nice, I found a veritable plug & play frequency counter and LDC display for in excess of $50 USD at Digikey. I didn't have to pay a tenth of that for the clock generator.

I have 1 $20, el cheapo, backup DMM for when I need to measure more than one thing at a time. It has a frequency counter/display. Therefore I would think there must be a way to get this functionality at a reasonable price.

I'm sure I'm over-thinking this and a simple solution is avoiding me. Any ideas on how I can count the number of clock pulses per second and display the results, (7 segment LED would be preferred)?


A small micro would do this easily. You can set up a capture compare peripheral to count input pulses and read/clear at a regular interval (e.g. 50ms - use a timer interrupt for this)
Then write result (after multiplying by necessary value - e.g. in above example: capture_result * 20 = Hz) to whatever display you have in mind.

A non-micro solution could be produced with some discrete logic ICs, there are quite a few designs floating around on the web. It would be a pretty "old school" solution but may be fine for a one off home project (and cheap) Here is a 0-40MHz example (from this page)

Discrete Logic Counter

For higher frequencies a small CPLD/FPGA would work well and would be a quick/easy HDL program to write - may be an idea if you have a small dev board lying around.

There are almost certainly dedicated ICs/Modules available if you have a look around. Most DMMs probably use an ASIC of some sort to provide multiple functions, though some of the cheaper models may use off the shelf stuff.

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  • \$\begingroup\$ Thank you for your suggestion. I was thinking it would be possible using maybe an ATtinyxxxx but was a little hesitant about programming. Might be easier for me to use an ATMEGA328 simply because I could use my Arduino to program the chip then remove it to put into my circuit. The speed is up to 20 MHz which should be enough, I suppose...but I was hoping for a non-micro solution. I may go buy a cheap DMM from Harbor Freight which has the frequency counter function and tear it open to see what was used. \$\endgroup\$ – rdivilbiss Jul 2 '12 at 23:56
  • \$\begingroup\$ Okay, no problem - I added a discrete logic example, and a bit more on other solutions. Maybe check eBay, there might be little frequency modules available at decent prices. \$\endgroup\$ – Oli Glaser Jul 3 '12 at 0:29
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    \$\begingroup\$ I am a fan of EEVBlog and can't imagine why I didn't check there. I love this sentence: "This circuit is ideal for adding a low cost frequency display to a function generator or other design. I doubt if it is possible to get a cheaper design using off the shelf components!. In fact, I challenge anyone to make a cheaper design using garden variety components!." Sounds perfect for my one off frequency/clock generator. In fact, knowing the reputation of the source, I am sure this is the answer I wanted, even before building it. Thank you very much! \$\endgroup\$ – rdivilbiss Jul 3 '12 at 1:55
  • \$\begingroup\$ Good stuff, glad to help - it being by Dave Jones is why I picked that example, as it's more than likely to be a pretty well designed circuit. \$\endgroup\$ – Oli Glaser Jul 3 '12 at 19:05
  • \$\begingroup\$ I agree. Dave Jones probably can be considered an above average souce of information. \$\endgroup\$ – rdivilbiss Jul 4 '12 at 2:14

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