3DR telemetry radio and Arduino observations…

A few interesting things I’ve learned that you won’t find in any manual or tutorial elsewhere…

  1. Minimum baud rate over the air is 57600
    Sure for most people this will be the minimum, but being fickle I decided to try the lowest setting 9600baud 8-N-1. Even with both sides of the links using this setting the information came over garbled. Changed both sides to 57600 and it was instantly fixed.
  2. Altering Transmit power
    You can change the transmit power from 1dB (1.3mW) to 20dB (100mW). You may think altering this transmit power level will reduce power consumption… WRONG! I think there must be a sink here because no matter the setting, you need to power the entire device off rather than lower the power level.
  3. Power savings
    With the GPS turned off (well, just keeping the RAM warmed up) by tracker consumes 27mA. These radios CANNOT be put to sleep when not in use, as per 2 above.
    I’ve used two Arduino digital GPIO pins to power the radio unit. One on its own wasn’t enough power. (You get a flashing red light on the radio unit to show there isn’t enough power being supplied – handy!). Using 2 pins from DIFFERENT sets of ports ensures the device is powered enough. Radio uses 28mA pretty consistently when pairing and sending data. (Must be different set to ensure you don’t max out the ATMEL chips’ max source power from one particular set of ports.
  4. Low cost alternative
    The 3DR radios are based on the ‘system on a chip’ Si1000 series chips for their entire radio operation. All the 3DR radios provide are the connections to a radio and to serial/usb. These radios retail from 3DR at USD 100 for a pair. The SoC they are based on is available for GBP 2.80 from a wholesale local IC stockist!!!
    Bound to be some way to build your own given that the schematics from 3D Robotics are all open source anyway. I’ll check this out and report back.
  5. Best Aerial
    The aerials that come with the radios are crap and are for WIFI not for 433MHz!!! You need a 15cm aerial or a 30cm dipole. I have a couple of antennae on order that should work well. I’ll check them out and let you know what range I manage.
  6. Power settings
    These radios can output up to 25dB, although the UK maximum is 10dB for legal requirements. People have reported a 7.6km strong link with dipole antennae and an external amp. I’ll test the range of each antennae option and let you know… For now its useful to know the power can be altered.
  7. Serial comms
    Arduino serial comms to these radios works at 9600 baud, but the connection itself seems to only work at 57600 (see 1 above). I can confirm though that I use Software Serial for these radios. This works well from an Arduino mini pro 05 3.3v 16MHz.

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