bitWrite()

Shift registers can be used to control multiple LEDs on your pinball machine. However, many times, you will want to change only one or two specific LEDs, and leave all the other LEDs alone. For this, we can use a new function called bitWrite().

Upload the bit-write sketch.

You should see only LED number 5 (start counting from 0) blinking. Inside changeserdata(int ff), we are using bitWrite():

if (ff == 0) { bitWrite(serdata[0], 5, 1); } else if (ff == 1) { bitWrite(serdata[0], 5, 0); }

The second argument tells bitWrite which bit (starting from 0) to write to, and the third argument, which can only be 0 or 1, tells it what to write it as. This leaves all the other bits untouched.

You can try these modifications without ‘saving-as’:

• Try changing the 0b00000000 assignment inside setup() again, and verify that the other bits are untouched.
• Try blinking some LED other than LED number 5. Try LED number 0.

CHECKPOINT!

You can use the flag to do more than just switch between two patterns. Try uploading the flagged-patterns sketch.

What are the red LEDs doing? Look into changeflag() and changeserdata() and see how bitWrite() is being used.

CHECKPOINT!

Back

Next