emonTH Multiple DS18B20 Sensors

Thanks to Dave McCraw it's now possible to connect multiple DS18B20 digital temperature sensors to the emonTH on the one-wire bus.

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Two External DS18B20 temperature sensor + internal DHT22 temp + humidity on emonTH

Multiple DS18B20 sensors can be (optionally) used alongside an internal DHT22 temperature and humidity sensor. Dave's sketch which is now up in the emonTH GitHub repo supports two DS18B20 sensors but can easily be extended to include more.

Dave's multiple sensor sketch requires the unique hardware addresses of the DS18B20 sensors hard-coded in the sketch, the 'emonTH temperature search' utility sketch can be used to discover the addresses.  Hardcoding the hardware addresses guarantees Emoncms inputs won't flip around if you replace or add sensors.

The multiple DS18B20 sketch includes all the low power saving tricks, the sensors are only switch on when required and the ATMega328 goes to sleep in-between readings switching off all unnecessary functions. Obviously running more than one sensor will consume more power but I would still expect battery life to be in the region of 12 months.

Using multiple DS18B20 external temperature sensors on the emonTH as lots of exciting possibilities, a few ideas include:

• Heatpump monitoring: inlet, outlet flow temperatures etc.
• Solar hotwater & hot water cylinder monitoring: top, middle and bottom of hot water tank
• Building temperature investigation: internal, cavity wall and external temperatures to inform openBEM (Building Energy Model)