Code to display an audio spectrum bar chart on the BBC micro:bit using the MSGEQ7 spectrum analyser chip - circuit schematic as shown.
The prototype was breadboarded and then transferred to a zbit:builder board (kindly supplied by http://zbit-connect.co.uk/). Due to the limited prototyping space on the zbit:builder, less experienced constructors might find it easier to use regular stripboard.
Video here: https://youtu.be/wQXjX3phBOo
The MSGEQ7 chip is available from Sparkfun and regional/global agents.
- https://www.sparkfun.com/products/10468
- https://www.sparkfun.com/datasheets/Components/General/MSGEQ7.pdf
Beware of buying the MSGEQ7 chip on ebay - some/many have turned out to be faulty and it's suspected that they are manufacturing rejects.
Schematic
On zbit:builder
(That's some mighty [fine/scary - insert as appropriate] circuit squishing going on there.)
How it works
The circuit built around Operational Amplifier U1 amplifies the signal received from the electret microphone and this signal is fed into the MSGEQ7 chip (U2) for sampling. The micro:bit program first resets U2 and the chip evaluates (samples) the amount of the input signal that corresponds to its first sampling frequency of 63Hz. A voltage proportional to the sample is output on U2 pin 3 and this is fed into the micro:bit and used to display a suitably-sized LED column on its display. The micro:bit then sends a pulse ('strobe signal') to U2 pin 4, which causes the chip to assess the microphone input at its next sampling frequency of 160Hz and output an appropriate voltage on pin 3 again, which is used for the next LED column on the micro:bit. This "sample - display - strobe' cycle is repeated for a total of 5 frequency bands, after which the micro:bit resets U2 to start over.
Notes:
- The MSGEQ7 chip sample frequencies are: 63Hz, 160Hz, 400Hz, 1KHz, 2.5KHz, 6.25KHz and 16KHz.
- The MSGEQ7 chip can perform total of 7 frequency samples, but since there are only 5 columns / bars on the micro:bit display only the first 5 frequencies are used.
- There's additional comments in the Python program file.