Hello, I have been working on a combination of the ultrasonic distance sensor (HC-SR04) with a temperature/ humidity sensor (DHT11) to correct the speed of sound in air. I am now trying to adapt it to cold climates (-15 degrees C). The Arduino does fine in the cold, as does the ultrasonic sensor. The temp sensor continues to operate but bottoms out at 1 degree C, but another independent sensor recorded -15 C (it was in a freezer and that should be correct). So, can I manipulate the code of the DHT11 library to get the sensor to operate that low? Or should I be looking for a temp sensor that has a lower range? Does anybody else have experience making sensors for ultra-low temperature environments?
The standard DS18x20 sensors work fine at -55 C.
+1 for the DS18B20
Check for the Dallas Temperature Control Library - http://milesburton.com/Dallas_Temperature_Control_Library -
wrt speed of sound, are you familiar with:
- http://www.rane.com/pdf/ranenotes/Enviromental_Effects_on_the_Speed_of_Sound.pdf - did some math here - http://forum.arduino.cc/index.php?topic=65205.msg493120#msg493120 - based on that doc
rajputq: The temp sensor continues to operate but bottoms out at 1 degree C, but another independent sensor recorded -15 C
I'm not familiar with the DHT11 but, if your results are erratic it may be down to the packaging, condensation etc. I can't speak highly enough of the DS18B20. All mine are in weatherproof package, and have been used in freezing conditions.
The DHT11 cannot measure below zero - it is in the specification - http://www.micro4you.com/files/sensor/DHT11.pdf -
Thanks for the replies everyone! I have used the DS18B20s in another project, and did not realize they had that capability, thanks! I had originally used the DHT11 as a single-pin reading of temp and humidity. The temperature was used to correct for distance, and the humidity was used to sense high humidity and turn on a fan to circulate air and prevent condensation, which seemed to keep the ultrasonic sensor working. Before the fan, it would give erroneous readings above about 40% humidity, after incorporating the fan to turn on at 40%, the ultrasonic could go up to 60-80% humidity, depending on how close the water level was, before getting wacky readings. I assume that the fan is preventing condensation on the speakers, which causes the erroneous readings. Anyway, I can use the DS18B20s for the next build, because with such extreme cold, the humidity shouldn't be an issue, as long as it stays cold (or I could get a separate humidity sensor). Thanks again for the help!