RF transceiver modules are great, but I've been wondering if one could be built using a picaxe and raw RF modules. Attached is a preliminary schematic.
The module has RS232 D9 male or female plugs (install either) and a max232. Or you could leave those components out for TTL. Transmission goes straight to the module via an inverter. Transmit also turns off the receiver for a short time so the receiver doesn't hear its own signal.
Raw RF modules can be as low as $2 for a Tx and $2 for a Rx, though this design has slightly more expensive ones (higher power Tx and more sensitive Rx). But you could use any sort of raw RF module.
The picaxe acts as a RF 'filter', in that it won't respond unless it gets UUUUU wakeup plus a valid header (eg ABC). A packet can be up to 14 bytes.
The RC time constant is affected by the baud rate. Eg at 1200 baud and 10ms you will need to wait at least 12-15ms after a transmission for a reply to come through. However, at the other end, it will have received 20 or so bytes and then has to process them and then send out 14 bytes (and then whatever is at the other end has to process them) and this will take at least 15ms anyway. At 4800 baud the RC time constant would by 1/4.
Serin hang is always an issue, and if one didn't want whatever chip was connected to this module (ie another picaxe) to be stuck in serin hang, one could always implement RTS and CTS via spare pins on the 08M - eg raise a line to say some data has arrived, then wait for the other micro to acknowledge it before sending on.
Can this be simplified further? Thoughts etc would be most appreciated.
The module has RS232 D9 male or female plugs (install either) and a max232. Or you could leave those components out for TTL. Transmission goes straight to the module via an inverter. Transmit also turns off the receiver for a short time so the receiver doesn't hear its own signal.
Raw RF modules can be as low as $2 for a Tx and $2 for a Rx, though this design has slightly more expensive ones (higher power Tx and more sensitive Rx). But you could use any sort of raw RF module.
The picaxe acts as a RF 'filter', in that it won't respond unless it gets UUUUU wakeup plus a valid header (eg ABC). A packet can be up to 14 bytes.
The RC time constant is affected by the baud rate. Eg at 1200 baud and 10ms you will need to wait at least 12-15ms after a transmission for a reply to come through. However, at the other end, it will have received 20 or so bytes and then has to process them and then send out 14 bytes (and then whatever is at the other end has to process them) and this will take at least 15ms anyway. At 4800 baud the RC time constant would by 1/4.
Serin hang is always an issue, and if one didn't want whatever chip was connected to this module (ie another picaxe) to be stuck in serin hang, one could always implement RTS and CTS via spare pins on the 08M - eg raise a line to say some data has arrived, then wait for the other micro to acknowledge it before sending on.
Can this be simplified further? Thoughts etc would be most appreciated.
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