Reply To: Sleep code not working with Maxbotix 7389

a. We saw no evidence that the sensor had any issue related to condensation during the tests given that there was a hydrophobic coating on the sensor face and that the bad data occurred at random temperatures as opposed to only when the temperatures were low.

That’s good to know. What was the fluoropolymer grease you used?

b. Reading out the serial data with a pause between digits rather than at normal speed seemed to help eliminate bad data when the weather was warm. But, this did not solve the problem when cooler weather arrived in the fall.

I’m not quite sure what your code looked like, but this doesn’t make sense, so of course it doesn’t make a difference. The Maxbotix talks to your Mayfly at 9600baud sending an R####\r every cycle (150ms-ish). That is exactly the rate that the Mayfly listens and records the data in. That’s not a changeable setting. Any “pause” you add in your code is just a pause in reading out from the buffer that whatever underlying serial library you’re using already stored the characters in. No matter the rate you read your data out from the buffer at, the input rate doesn’t change. The only caveat to that is that SoftwareSerial is just pretending to be a serial port and so it’s possible to throw off the character accuracy if the processor is doing too much when the characters come in. The result of the SoftwareSerial errors would be total garbage though (as in not even printable characters), not readings like “R0300\r”.

c. There was no bad data during the testing of the sensor with continuously power independent of the Mayfly, including at temperatures well below freezing.

Good to know it works. Good to know. Assuming you’re not manually triggering the sonar every time, that’s the internal range filtering doing its job. I’d guess you could get similar results by powering up the sonar just 5-10 seconds before taking a reading. Based on the spec sheet, it takes 5 readings for the filtering to take effect. It doesn’t specify the maximum number of readings the filtering considers, but the sonar “boots” up in ~160ms and, as long as pin 4 is left floating, completes a reading every ~148ms. So if you power up the Maxbotix for even 10s before you accept readings (10s before opening your serial port that is) it will have already had a chance to take over 60 readings which is probably plenty for good filtering.