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# frequncy counter

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#### grrr_arrghh

##### New Member
Hi

Anyone have any idea how to build a frequency counter? So i can connect the output of (for example) an astable to the frequency counter and it will give me the a readout of how many Hz the ouput is oscillating at.

I realise that this could be done using an Oscillascope, but i'm only a poor student.

Thanks, any ideas much appreciated

Tim

A simple Phase locked loop could be used as a frequency to voltage converter which could be read with a volt meter. It would only be good for a specifoc voltage range but it would be cheap. If i remember correctly all you need is a XOR gate to do a phase comparison (will output a 1 for the time the two signals are out of phase), an opamp configured as an integrator (phase to voltage converter) and a voltage controlled oscillator. After the circuit reached steady state the output of the opamp will be proportional to the frequency. The frequency range would be limited by the VCO's output range.

Hope this helps

Brent

Frequency Counter

The frequency to be measured must be sent to the clock input of a 40110BE. Set up a monostable to go to logic 1 (high) after 1 second from when the frequency to be measured enters the circuit. The output of the monostable must to pin 4 to freeze the count after a second. If the 40110BE is connected to a 7-segment display you will see the frequency measurement minus 1 (this is as the count starts at 0! So for the actual frequency add 1 to the value on the display). Please note that a single 40110BE can only measure frequencies up to 10Hz you will need to cascade many together to get higher frequencies. 3 40110BE’s will measure up to 1KHz. If you are confused then I can try and explain better.

Frequency Counter

:idea: This could depend on what parts you have available. One solution is to base your design on a simple decade counter with a store control (display held but keeps on counting), and reset control (resets counter to zero). You would then need to generate a 1Hz pulse fed in to a dual mono-stable (eg 4528 or 4538). The first mono-stable has it's output controlling the display store (normally held), the falling edge will trigger the second mono-stable whose output will reset the counter.

Basically this creates a 1 second window in which the pulses from your signal will be counted. At the end of this window the result is displayed and is proportional to the frequency of the signal being measured. This is then repeated for the next second.

Hope this helps? This will my first reply to a tech problem, so would welcome any feed back.

Trev

Do a Google search for "frequency counter schematic". I got several promising hits.

thanks for the quick replies eveyone.

i'm looking at the diags found on google (thnks ron), but if they are too conplicated (!) or too expensive then i'll be back!! so don't go anywhere as they are all good ideas

thanks again

tim

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