The blog of 'The Arduino Guy' aka Mike McRoberts, author of Beginning Arduino.

17 October 2014

Wireless Sensor Node - successful transmissions

Friday, October 17, 2014 By

If you've been following the blog lately you would have read about the issues I had with transmitting data packets over a wireless netwrok between two Arduinos using an RFM69CW radio transceiver module.

A quick recap - I first had lost packets and lots of CRC errors in transmissions. These turned out to be a bug in the Jeelib library. Then I put an L7805 5v to 3.3v rectifier on and found it wasn't suitable. This caused lots of problems with the radio. Changed that to an MCP1703-33 which is much more stable and better suited to battery operation too. That fixed those issues.

Then I found out that I couldn't connect any other SPI device to the BUS as the RFM69CW also uses SPI and is controlled via timer interrupts. This was corrupting comms over the SPI Bus to any other devices as the interrupt was hijacking the bus on regular intervals. I tried a DS3234 Real Time Clock IC and the data were all wrong.  I could bit-bang another SPI bus on non SPI pins but this is a lot of extra work. Instead I opted to switch to an I2C RTC (DS1307). I'll make sure all the sensors I use are I2C to avoid any further problems.

So, now i've discovered the above limitations with the hardware and software and have a better understanding of what i'm up against i've made a lot of progress. The sensor nodes are now transmitting data successfully with no lost packets or CRC errors. I have yet to do any range tests yet or run them of battery (with power saving sleep modes), that is the next stage in the project..


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