micro:bit radio signal strength meter

A radio signal strength (RSS) meter for the BBC micro:bit.

Run this on a couple of micro:bits, to measure their radio signal strength at different radio transmission powers and distances.

We used this to calibrate RSS for range-finding for our hermit crab project at Dinacon 2018.

Installation

1. Install pxt
2. pxt deploy compiles and deploys the project to a connected micro:bit

You can also (1) create a new project on MakeCode, (2) click {} JavaScript at the top of the page, (3) paste the code from main.ts into the edit pane on the right, (4) and click “Download” to download a *.hex file to copy to the micro:bit.

Usage

The left button cycles between display modes:

• Grid (default): The top row cycles when packets are received. The remaining four rows are used to display the received packet signal strength. The top left corner of this rectangle is -42 dB; the bottom right rectangle is -128dB. The last few samples are faded; this makes it easier to eyeball a trace of the signal strength history.

  In this mode, button B briefly displays the last received packet signal strength.

• The absolute value of the last received packet signal strength. The absolute value is used because the number is scrolled across the display, and the negative sign makes this take even longer.

• Transmission value (0 or 1), and receive value (0, 1, *). When the receive value is 0 or 1, the meter only attends to signals that match this value.

  In this mode, button B cycles among the values.

• Current radio transmission power.

  In this mode, button B cycles the radio transmission power from 0 to 7 and back to zero again.

Motivation

Created at Dinacon 2018, for use in developing Dinacrab.

Branches

• threshold adds hysteresis to proximity sensing, to reduce flapping. Proximity is set when the signal is high, but is cleared only after it has spent some time low.
• transforms uses a button to cycle through different transforms that are applied to the signal strength before it is displayed. Since the transforms are all monotonic, this doesn't affect an algorithm that's conditionalized on RSS thresholds in any substantive way (simply apply the same transform to the thresholds), but it can simplify eyeballing the meter.

License

MIT