I'm working to create an ultrasonic sensor to be used in object recognition. I've been studying various schematics and current sensors on the market - the most common being the HC-SR04. When viewing these alternatives I've found that several use a hysterisis comparator for their conversions, but this adds a time delay. I was thinking if it could be converted into a strict threshold schmitt trigger it could serve the same purpose without the time delay.

Any experience with this conversion, or an idea of how to make the conversion would be great. Below is a sample diagram from the HC-SR04 schematic for the comparator that would need to be changed into the schmitt trigger.


Any advice on whether a transistor or op-amp solution would be better is also appreciated. Currently leaning toward op-amp as it is easy to design and manage the multiple thresholds necessary for rise and fall edges.

  • \$\begingroup\$ How strict threshold do you want ? A comparator will be the best, for sure. \$\endgroup\$ – Long Pham Jun 11 '18 at 14:42
  • \$\begingroup\$ Due to potential fluctuations in the echo I would want the threshold to be set within a .03V range on both sides if possible. Even with the time delay it would be best to use the comparator over a schmitt trigger? \$\endgroup\$ – Aruss Jun 11 '18 at 15:09
  • \$\begingroup\$ Few schmitt triggers will allow you to set the range whereas most comparators do and 30 mV offset is no issue for many of them. \$\endgroup\$ – winny Jun 11 '18 at 15:42
  • \$\begingroup\$ A better way to write this question would be to define your requirements and then ask a specific question. \$\endgroup\$ – laptop2d Jun 11 '18 at 16:44
  • \$\begingroup\$ Will you want to vary these hysteresis thresholds as the received signal gets bigger and smaller? \$\endgroup\$ – Andy aka Jun 11 '18 at 16:57

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