Bitkit - Colour Sensing
The micro:car has a colour sensor at the front. This allows you to be a little more inventive with your line following applications.
The image shows the car moving autonomously on one of the tracks that come with the kit. I have used the markers from the kit to colour in some sections of the track. You can see a blue circle, a red rectangle and, just off the bottom of the image, is a green circle.
The following program code uses the Drive and FollowLine procedures previously developed to follow a black line and do something when different coloured sections are reached. When the car reaches a blue circle, it makes a 90° turn to the right. When it reaches the red rectangle, it stops for a few seconds. When it reaches a green circle, it makes a 90° turn to the left.
from microbit import * def Drive(lft,rgt): ld, rd = 0, 0 if lft<0: ld = 0xff lft += 255 if rgt<0: rd = 0xff rgt += 255 i2c.write(0x28,bytes([1,lft,ld,rgt,rd])) def Follow_line(): i2c.write(0x27,b'\x02') ln = i2c.read(0x27,1) drv = [(0,0),(255,255),(255,255), (63,255),(0,255),(255,63),(255,0)] lt,rt = drv[ln] Drive(lt,rt) sleep(20) def Colour(): i2c.write(0x27,b'\x01') return i2c.read(0x27,4) while True: c = Colour() # check for red(2), green(3), blue(4) if c>=2 and c<=4: # colour event if c==2: # stop for 2 seconds (red) Drive(0,0) sleep(2000) Drive(255,255) sleep(1000) elif c==3: # turn left (green) Drive(255,255) sleep(750) Drive(0,255) sleep(1800) Drive(255,255) sleep(500) elif c==4: # turn right (blue) Drive(255,255) sleep(750) Drive(255,0) sleep(1800) Drive(255,255) sleep(500) else: Follow_line()
The key to this is the Colour function. To get a colour reading, we write a 1 to the colour sensor. We then read back 4 bytes and look at the value of the first byte. The number returned tells us which colour was sensed,
- Another Colour
This feature of the micro car is pretty cool. Notice that the values you can get from a reading correspond to the 3 colour channels plus black. This is easiest to work out with a colour sensor. Other colours are a little more tricky to read reliably - but not impossible...