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Thread: Low Rate Wireless sensors with Teensy3

  1. #1
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    Low Rate Wireless sensors with Teensy3

    I've been working with a 5 node wireless sensor experiment.
    Radios: Mix of HopeRF RFM22B (SiLabs 4432 chip) and Dorji (sold by Tindie.com) also using the 4432 chip. Both PCBs are the same size. (there is one line of code to change between the two).
    SPI between Teensy 3 and radio.
    The Dorji radios are $4. https://www.tindie.com/products/DORJ...rduino-picaxe/ The docs are on the Dorji web site.

    Used with the excellent RF22 library for Arduino and Teensyduino by Mike McCauley, and my simple test applications.
    Running ReliableDatagram (ACKs with retranasmissions for error correction) in a star topology. (RF22 lib also has ad-hoc mesh topology option).

    One of the 5 nodes is a Teensy3 with a piggy-back radio, no separate PCB or breadboard. The piggybacked radio is less that 1/3 the size of the teensy.
    This one was plugged into a "USB battery" similar to http://www.frys.com/product/7888039?...H:MAIN_RSLT_PG .
    then put into kitchen freezer (stainless steel on 3 sides, steel on back). Antenna is just 8 in. of wire. 433MHz. 17dBm power (about 50mW).
    so far, plenty of signal strength at other end here two rooms away: -75 to -80dBm (receiver might work OK at -100dBm. Set to use 19200 bps GFSK; could be set as low as 1200bps to operate better at weak signals). Can be configured for 56Kbps and up if the SNR permits.

    Radio has on-board temperature sensor that uses the 4432 chip's A/D. It's reporting -16C quite reliably.
    The Teensy 3 inserted a message: Please send hot tea and a blanket.

    The Dori module has thru-holes as well as castellated connectors. On 1mm centers. Steady hand required in hand-soldering.
    Foam mounting tape, double-sided adhesive, was used to secure the module, plus stiff ground wire.

    ENCLOSURE
    Click image for larger version. 

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    Last edited by stevech; 03-28-2014 at 08:28 AM.

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