Hi,
New here and just build my first EmonGLCD. I have uploaded the Tester sketch and all works fine except for the temperature indication which always reads 0.0°C. I have checked my soldering and everything seems OK. Is there some way I can test the DS18B20 Digital Thermometer with a multimeter to see where it's going wrong?
Re: EmonGLCD Temperature Sensor always reads 0°C
Basically - no. It sends back a digital stream of data. A multimeter will tell you whether the supply is there (3.3 V), but little else - the output (Data - DQ on the data sheet) will be 3.3 V but pulled down as it is interrogated and responds.
The normal fault indication is not 0.0°C, with no sensor connected you normally see "-127.0C". Connecting only GND & Data I get "85.0C".
You haven't accidentally edited the sketch, by any chance?
Re: EmonGLCD Temperature Sensor always reads 0°C
Hi,
Not done any editing of the sketch at all. The 3.3V at GND are both OK. Connection of data line to processor checks out OK with multimeter.
After that I did edit the sketch to display instead of temperature a device count using:
numberOfDevices = sensors.getDeviceCount();
This returns 0 so I'm guessing the sensor can't be seen. Other than getting a new sensor I can't see what the problem would be unless there is a mistake in the downloaded tester sketch that I can not spot (guessing, as it's downloaded and nobody else has reported this problem, there are no mistakes in the sketch).
Re: EmonGLCD Temperature Sensor always reads 0°C
That's weird. As you've checked continuity I think it has to be a faulty sensor.
If you can get the sensor out and tack it into an emonTx, download the temperature_search sketch to get its serial number and that can't see it, then it's almost proven it's the sensor.
If it is faulty, drop an email to the shop (if it came in the kit).
Re: EmonGLCD Temperature Sensor always reads 0°C
After a little more investigation it was noted sometimes when I connect the power the EmonGLCD powers up (3.3V OK) and nothing happens except the LCD backlight just flashes but other times it works OK (except the temperature reading 0.0°C). If I disconnect the Vcc from pin 3 of the DS18B20 then it powers up OK every time but still reads 0.0°C. I tried the DS18B20 in parasite power mode and it power up OK every time but still reads 0.0°C. I've ordered a new DS18B20 and disconnected the existing one. However, as said above it seems strange the indicated temperature is 0.0°C and not -127°C.