# Can't detect short pulses with GPIO

**URL:** <https://community.particle.io/t/cant-detect-short-pulses-with-gpio/16682>\
**Category:** Troubleshooting\
**Created:** [October 18, 2015, 10:41pm UTC](https://community.particle.io/t/cant-detect-short-pulses-with-gpio/16682 "2015-10-18T22:41:53Z")\
**Posts on this page:** 1\
**Showing post:** 19

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**Author:** ![Arthur\_dent\_42\_121](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@Arthur\_dent\_42\_121](https://community.particle.io/u/Arthur_dent_42_121)\
**Post date:** [October 19, 2015, 2:23pm UTC](https://community.particle.io/t/cant-detect-short-pulses-with-gpio/16682/19 "2015-10-19T14:23:05Z")

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Yup, the code I tested above was yours, with my triggering code.

In regards to your previous comment, I have confirmed that the pin I’m using is the right one, and I’ve tried using a different one.

D1 drives a h-bridge at 40khz, sending an ultrasonic ping out of a transducer. This bounces off a wall and goes into another transducer. Then, I have a notch filter and a two stage amplifier that brings the recieved pulse to 3.3v amplitude so we can detect it on D3 digitally. DAC1 sets the threshold on a comparator on the receiver.

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