An idea I liked on the micro:bit web site was the speed trap. Make a pair of timing detectors from aluminium foil strips, attach them to pins on a micro:bit, put some foil on the bottom of a model car, and run it between the gates. Then count milli/micro (!) seconds between triggerings.
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| Fynn testing the speed trap |
In the picture you can see the alu foil strips, attached with double sided tape to the Lego Board. ("Lego Board - a large square plywood tray with 1/4 round moulding screwed to the edges, to prevent Lego falling off. This particular one is probably 35 years old!!). Micro:bit is running a very simple programme, shown below.
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| Micro:bit code |
This doesn't actually work so well - I have removed the Speed calculation and display, as it appears that micro:bits only do integer arithmetic and so since the speed is < 1 m/s it only shows 0! So we're just taking the msec readings. It takes about 430msec to traverse the 0.5m track at the current angle to the horizontal. An opportunity to check gravitational constants?
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| Car with triggering aluminium foil |
The car has a strip of alu foil (more double-sided tape!) attached to the bottom, with a spring made out of the backing from the tape rolled into a loose, springy roll that just pushes the foil onto the surface. Seems to work fine!
I shall take this to the Kode Klub next week, as an interesting demo of what's possible with a bit of thought. Fynn really enjoyed seeing it done, and hopefully had some idea about what was going on.
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