[OpenTRV-dev] V0.2-Arduino: getting started

Thu Apr 4 11:37:54 BST 2013

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To: "Closed list for developer discussions" EMAIL ADDRESS HIDDEN 
Date: Thu, 4 Apr 2013 11:05:37 +0100 (BST)
> Apologies for the delay.
> I've actually been thinking about what would make an ideal boiler / valve
> control node for me. On the basis that (hopefully!) the weather won't call
> for heating too much longer, and that my current tank thermostat keeps
> arcing, that might be a good place to do "summer hacking" for me.
> I have got round to having a look into the RFM12Pi. It's basically an
> ATTINY84 with an RFM12 connected to the SPI and it bit-bashes serial data
> to and from the Pi on 2 other Io pins. 3 spare pins are brought out to a 3
> pin header so I guess these could be employed to drive valves. It might
> also be possible to read Onewire temperature sensors on one of the spare
> pins, I guess. The serial protocol is a very simple human-readable ascii
> command driven affair, so I don't see a problem with extending that.
> I keep wondering if a very simple node talking to a Pi, which can give me
> web access to set the schedules, etc. is what I want or whether this
> should be a more autonomous "boiler programmer" with "advance" buttons,
> scheduler, RTC and maybe even a user interface to program it manually.
> I keep think that the RFM12Pi is a bit too minimal to cope with what I
> might want to throw at it. I might build something around a more powerful
> AVR, containing some switching for the valves, and see where that takes
> me.
> I wonder if I should still connect it to a Pi, or give it an ethernet
> interface?
> Kevin

Hi Kevin,

I have designed a dual-RFM23B board for the Pi which has an optional 1-wire interface. Prototype PCBs are on their way from China as we speak. Assuming it all works properly I'll release the design and should have a few for sale in about a month, so maybe this would be of interest to you? I'll price it up when I get in this evening.

Feature summary as follows:

- 1x RFM22B/RFM23B at 868 MHz
- 1x optional RFM22B/RFM23B at 433 MHz
- I2C to 1-wire bridge
- Real-time clock with lithium battery backup
- ATMEGA328 with serial connection to Pi, SPI bus master for TRXs
- Bus routing logic to enable the Pi to be SPI bus master. This allows the Pi to program the AVR without an external programmer, and also to communicate directly with the TRXs.

I have also done some work on a standalone ethernet/RFM23 bridge board based on ARM Cortex M4, but I will probably keep this on hold pending some clarification of the future availability of the HopeRF modules.




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