The greenhouse project
Radio
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Radio modules
The radio modules are very simple to interface. The transmitter uses its own supply voltage, preferable more than 5V to increase transmit power. As the device is basically analogue, I have to adjust the TX signal from 0/5V to the full swing of the TX voltage. An OP-amp takes care of that, i.e. changing 0/5V to 0/V+.
There is also a transistor used to turn on and off the module. Both to save power and also to turn the transmitter of when not sending.
I use just 20cm of wire for antenna. It works well enough in my setup.
The connector is power, ground, TX and enable (turn power on).
 Transmitter |
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The receiver is even simpler to interface as it works at 5V.
The antenna is again a 20cm wire connected to the RF input.
Included in the circuit is a transistor to turn on/off the module. This is only used to save power.
The receiver module has a carrier detect output but unfortunate it didn't work as I hoped. It is outputting a signal strength signal that must be measured using an A/D input. The output only differs a few hundred mV when the transmitter is on or off. Instead of using it to see when data is received I check for a few preamble bytes in the data stream.
The connector is 5V, ground, RX, CD and enable (turn power on).
 Receiver |
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My interface module is also based on the BX24 chip. As the logger it has connectors for both TX and RX modules, even though I only use RX at the moment (TX at the logger).
Basically it receives bytes from the RX module, looks for data in the byte stream. If it finds data (a valid packet with correct CRC) it decodes it and send the result as text to the connected PC. I will probably change it to do the decoding in the PC instead. In this case I don't have to change the interface modules program if I decide to send other data from the logger.
 Interface |
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