This is my second project with a BBC micro:bit. Normally I wouldn't apply for 2 projects with the same device but in this case the first road test got derailed by delays in releasing the micro:bit. Nine months after “winning” the first road test the device still had not shipped and there was no information about the status of the road test. It looked like they were re-issuing the road test as a big ideas challenge and since I had designed some circuit cards for the road test, I re-applied with a slightly different objective…. outlined here:
Then, of course, the micro:bit from the first road test arrived and I produced a review based on my first proposal …. putting the device through some rudimentary tests and introducing methods of prototyping with it, including connecting it to a breadboard via an elastomeric connector:
The Big Idea
Many other reviews have been published, so this big ideas challenge will take things a bit further to try and interface a low-cost LCD and keypad to a micro:bit.
The circuit board I designed to interface these peripherals has a power switch and some circuitry to connect a battery, but it was designed before the micro:bit power section was redesigned. (this micro:bit redesign was part of the reason for the delayed launch of the micro:bit). However I think the interface circuit board will still work okay.
Here are some unboxing videos that introduce the “big idea” and they can be compared with the unboxing video from my first road test:
Although this is not a formal road test (and there is no road test form to fill out) I thought it would be interesting to contrast this unboxing with my previous road test - see the link above.
The camera does not do a great job of capturing what LEDs look like - the camera pixels are so saturated they don't accurately capture LED colour and the saturated area leaks to adjacent pixels causing a halo effect. The diffuser actually makes the LEDs much more readable.
A note about elastomeric connectors: They contain many narrow rectangular vertical connections embedded in an elastomeric strip. The closely-spaced vertical connections have narrow rectangular footprints, often allowing multiple connections to the same pad. Each connection has an associated resistance which depends on the connection material used. Some elastomeric connectors use micro-wires with very low impedance, others use a carbon filled compound which may have a resistance of a couple of hundred ohms for each connection. When multiple connections contact each pad, the total impedance is effectively lowered by the parallel combination of connection impedances. In this case the power and ground connections have many connections, so the effective resistance is fairly low even though I am using carbon-based elastomeric connectors. It is almost like the edge card connector on the micro:bit was designed for elastomeric connectors with much larger power fingers.
The fact that there is resistance in the connections is also good from the point of view of protecting the micro:bit from connection mistakes – digital outputs cannot be directly shorted to a power rail.
Micro:bit pinout: https://www.microbit.co.uk/device/pins
Note the 3 SPI pins and the 2 I2C pins that I use for the LCD and keypad respectively.
The LCD uses these 5 signal pins (to stay away from LED and analog pins):
- P11 - LCD reset
- P8 - LCD SPI chip select
- P16 - LCD data / command select
- P15 - MOSI - LCD data
- P13 - SCK - SPI data clock
Demonstration of the big idea - a BBC micro:bit driving a low-power, cost effective Nokia 5110 graphics LCD.
The LCD opens up many more applications for the micro:bit.
- connect a capacitive keypad using I2C
- figure out how voltage is regulated on the micro:bit and connect a slim battery
- 3D print a complete case
- try connecting 2 micro:bits via Bluetooth
micro:bit reference links:
BBC micro:bit home page: https://www.microbit.co.uk/
micro:bit coding page: https://www.microbit.co.uk/create-code
micro:bit MicroPython: https://microbit-micropython.readthedocs.io/en/latest/
micro:bit IoT: http://bluetooth-mdw.blogspot.ca/p/bbc-microbit.html
micro:bit Bluetooth: https://codethemicrobit.com/reference/bluetooth/bluetooth-pairing
micro:bit power consumption: http://www.reuk.co.uk/wordpress/microbit-power-consumption/
android & ios apps:
9 micro:bit projects: http://www.itpro.co.uk/desktop-hardware/26289/nine-top-bbc-micro-bit-projects
7 micro:bit projects: http://www.bbc.com/news/technology-35824446
6 micro:bit projects: https://www.codeclubprojects.org/en-GB/microbit/