Building the hardware

See the Hardware folder for schematics and photographs.

Version 1 of the hardware has:

• Four thermocouple inputs for propagator heating control.
• One humidity sensor input (on a DIN connector).
• One air temperature sensor (one-wire) for air heating control. In the photo the sensor is directly soldered to the DIN connector, but this is subsequently on the end of a wire to place the sensor near plants.
• One light sensor. This is mounted behind a drilled hole on the back panel (pointing out of the greenhouse away from lights to be controlled). A thin plastic membrane is cut to cover the hole, secured with the screws holding the light sensor.
• Eight relay outputs providing mains power to each controlled item.
• Nine LEDs on the front panel - one for the state of each relay and one to indicate when power is applied.
• A Raspberry Pi prototyping board with connections for humidity sensor, light sensor, one-wire temperature sensor, LEDs and relays. A link from this board goes to a second board for the thermocouple ICs.
• A PSU provides power to the Raspberry Pi (I had a redundant European USB phone charger and carefully cut the mains pins off without damaging the wires.

Safety note:

• This is mains powered so be careful!
• Maintain separation between the mains power input and output.