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Thread: Using FrequencyMeasure with 555l pulse generator

  1. #1
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    Using FrequencyMeasure with 555l pulse generator

    Hi There!,

    I'm very interested in using the FrequencyMeasure library to measure low frequency light waves. Up to now I just have an Adruino Uno but if the project develops I can see I would be better to get a Teensy.

    To test the frequency measuring part of the project I am using a 555 timer ic pulse generator set at 100Hz approx. see circuit

    https://drive.google.com/file/d/0B7p...it?usp=sharing

    I have connected the output to digital pin 8 on the uno and grounded the circuit to digital gnd on the board. The problem is that the output is not working. When I connect the signal to pin8 I get a random frequency in the results (either serial monitor or LCD) when I take the signal off the pin the value changes to another random frequency and if I touch the pins again another value is output etc.

    I am just a beginner really with electronics and have little experiance with these microcontroller platforms so I would be greatful of some help and advice.

    My questions are firstly:-

    Can I use that circuit 'as is' to provide the signal. or is it inadequate in some way?

    Should I be using the digital ground as a common ground for the external circuit?

    What is likely to be the issue causing the failure to measure the frequency correctly?

    my gut feeling (not very scientific) is a problem with the signal i.e. strength, waveform, voltage etc.

    Cheers

    Nigel
    Last edited by Bignige; 02-19-2014 at 04:50 PM.

  2. #2
    Senior Member PaulStoffregen's Avatar
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    Is that 555 circuit sending a 9V square wave into the Uno's pin? If so, that would be bad...

  3. #3
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    No, I've put a voltage divider in to bring the output to less than 5v. Measured it to around 3v . Is there a way to test the pin to make sure it hasn't been blown?

  4. #4
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    After further investigation with the help of an oscilloscope I determined that the output if the signal was the cause. For some reason the circuit us not providing a pulsed signal. By using a basic astable 555 timer circuit I got the desired square wave signal. Hooked it to the arduino with frequencymeasure running and it works fine. I just need to find out why the original circuit didn't produce pulses.

  5. #5
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    The circuit as drawn is fine. I just had a wiring mistake. So circuit and frequency measure work together on the arduino uno. Measured frequencies from 12Hz to 1200Hz in tests.

    Now to plan my project!

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