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Meassuring frequency of external signal

jelinpe7
Associate
Posted on February 14, 2015 at 12:39

Hi, is it possible to meassure frequency of external signal via Input capture, if the external signal is only from 0,5V to 2,5V (not from 0V to Vdd - 3V) and it is sine wave (not square wave)?

Thank you

2 REPLIES 2
raptorhal2
Lead
Posted on February 14, 2015 at 15:22

Check the ''I/O Port Characteristics'' section in the data sheet for your device. For example, the F405 minimum signal voltage is 2 volts.

Sine or square wave shouldn't matter, but the measured frequency for each sample will be more effected by signal noise for the sine wave.

Cheers, Hal

Posted on February 14, 2015 at 16:18

There is a schmitt trigger on the input, it should be able to do a reasonable job of thresholding the signal as described.

Depending on the frequency you'd either want to count the number of pulses over a observation interval, or use the input capture to measure the period of a single cycle (or multiple using the input prescaler).
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