Make Electronics

Experiment 36: The Lock, Revisited

312 Chapter 5

say that the value will be between 71 and 83. If we specify a range as shown in

the following table, we have a much better chance of interpreting each button

correctly.

Button number Range

9 600 71–83

6 700 84–96

3 800 97–108

0 900 109–121

8 1000 122–134

5 1100 135–147

2 1200 148–160

7 1300 161–172

4 1400 173–185

1 1500 191–198

Suppose you attach the common pin of your keypad to ADC Logic Pin 2 of the

PICAXE. You can now use the Program Editor to write a program that looks like

this:

getkey:

readadc 2,b0

let b1 = 9

if b0 < 84 then finish

let b1 = 6

if b0 < 97 then finish

let b1 = 3

if b0 < 109 then finish

let b1 = 0

if b0 < 122 then finish

let b1 = 8

if b0 < 135 then finish

let b1 = 5

if b0 < 148 then finish

let b1 = 2

if b0 < 161 then finish

let b1 = 7

if b0 < 173 then finish

let b1 = 4

if b0 < 186 then finish

let b1 = 2

finish:

return

What does the word “return” mean at the end? I’ll get to that in a second. I want

to explain the rest of the routine first.