Hi Everyone,
I have designed a 433mhz temperature probe using an ds18b20 as the probe. The probe connects to an RJ9 connector. The design uses an nrf905 transceiver, and an atmega328P. It is designed to run with an ER14505 battery. There is support for running off external power, as well as support for battery monitoring via ADC, and 2 external ADCs which can either be 0 to 5v or 4 to 20ma (with 24v 4 to 20ma current loop). There are 2 external inputs and 1 output. It uses an mcp23s08 as an IO Expander.
I am wondering if you can take a check at my schematic and let me know if there are any problems either with the part values or how they are connected.
If you find this design useful please let me know. Please also add any suggestions/recommendations.
Thanks and Regards,
Steed.
The one-wire part of this is 0.001 percent of the circuitry.
Is there some reason for all this microprocessor stuff and home brew RF for just a wireless temperature sensor?
Or is it a class assignment and you had to do this complex solution?
Hiya,
Thanks for your responses. Indeed the 1-wire stuff here is a very small part of the circuit, as its implemented via bit-banging the protocol. The ds18b20 temperature probe was chosen because its relatively cheap, accurate and easy to work with. The ADCs and IOs are so that the board can be a generic remote monitoring station for many things. The idea is to put a couple of them around a home to monitor doors, windows, etc, and with one in the garage, the output can be used to open the door or whatever. I will have another board with a ready made nrf905 module on it, and that will be used to perform 433mhz comms with 1 or more of these remote sensors. Perhaps it is overkill, but I wanted something fairly easy to work with. And its not entirely homebrew on the rf section as the nrf905 does all the hard work for you. What would you recommend instead for short range RF comms ? So far this seems to come in a lot cheaper than opting for wifi/bluetooth/xbee. Also, by changing some of the inductor/capacitor values, the nrf905 can do 868 and 915mhz too. I also did extra circuitry so that it can run either via battery or an external power supply. Sometimes its a lot easier to use rf comms than running cable everywhere. Do you see any suggestion that it may not work, or that parts of it may not work ?
Regards,
Steed.
I’d use an off the shelf board.
Teensy AVR or Teensy ARM.
Or Coridium board with XBee socket.
Just out of curiosity, did you look at this post: https://forum.sparkfun.com/viewtopic.php?f=14&t=35297
BTW, the design looks very good
Hey Thanks, I just hope it works, I was hoping to get some feedback before I build it. I had not seen the other thread, however it does look interesting, thanks.