So far I have two temperature and humidity nodes...
The hardware and software are really simple compared to any wireless solution. These two nodes are polled every now and then and the average temperature in the house is calculated. This will eventually switch the central heating on and off.
The 'controller' is simply a PC connected to the RS485 network via a bit of hardware. The hardware does the automatic switching of the RS485 transceiver between Rx & Tx. There is also a current limited regulator to provide 8V at 200mA. All this is piped round the house through CAT5 cable.
The PC software is written in JavaScript and executed with node.js. The user interface is via a browser on any capable device on the IP network.
The two temperature / humidity nodes were installed quickly and I soon required more nodes. Hand building prototypes is fine but when more units were needed I did a PCB using EasyEDA and ordered them from JLCPCB. Two weeks later, PCB's arrived.
Nice. The PCB's were good quality and its not really worth etching boards at home anymore unless you need a PCB within the next few hours!
The PCB contains the RS485 comms stuff and a 5V regulator. 'Functionality' such as the temperature sensors can be added in the 'prototype' area.
The boiler and front house lights require a relay switch to operate them. Rather than having a relay eating into the power budget of the system I used relays with a coil rated at 12V and ran them at 8V. The circuit below was used to boost the voltage to the coil at switch on, reducing the coil voltage once it had switched.
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| Voltage boost relay driver |
This circuit provides a voltage pulse of just under twice its supply voltage to the coil. It also provides a turn off delay, determined by the charging of C1.
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