I'm hoping someone can help me "bench test" a DS18B20 temperature sensor attached to my Opentherm Gateway, without needing to connect the OTGW to a boiler or thermostat. So far all my attempts to get a non-zero temperature reading have failed.
The OTGW is from Nodo Shop (PCB version 2.4, with PIC16F1847) and is running firmware 6.6. I am using the PC-based monitor tool, also version 6.6.
The hardware has been modified as described, that's to say jumpers JP1 and JP2 are no longer bridged, and there's a 4.7 kohm pull-up to GPIOA on GPIOB. I've confirmed that both GPIOs can be driven independently to 0V and Vcc (using GA/GB=1/2) and read back correctly using PR=I. A DVM confirms that the correct voltages appear on the outputs.
My test procedure is:
- leave the gateway disconnected from a boiler or thermostat
- connect a DS18B20 temperature sensor to GPIOA (Vcc), GPIOB (data) and GND
- power up the gateway via USB
- connect the PC-based monitor via USB COM port
- configure the GPIOs for the temp sensor (GA=2, GB=7)
- confirm the configuration with PR=G (reports 27)
- configure the temperature sensor to be outside temperature (TS=O)
- confirm the temperature sensor configuration with PR=D (reports O)
- request the outside temperature with PR=E (reports 0.0)
Scoping GPIOB shows that it remains at Vcc throughout: there are no transitions at all (other than the expected positive edge during start-up). It seems that the gateway is not communicating with the temperature sensor, even when the PR=E command is issued.
Not surprisingly, replacing the DS18B20 with a different one makes no difference to the behaviour.
I wonder whether the gateway software is not communicating with the temperature sensor because it has no connection to a boiler or thermostat.
In short: is it possible to test operation of the DS18B20 temperature sensor without connecting to a thermostat or boiler, and if so how should this be done? If there is a mistake in my test procedure, please let me know.
Many thanks,
Ian