The circuit now functions as follows. When the asterix is pressed the LED on the right side of the circuit is lit. While this key is pressed the code 1-4-7 is pressed. Next the LED just above the 555 is lit for a brief moment. Then the relay flips on and the green LED lights up. To flip it off again I have to press the hashtag on the keypad, the relay flips off and the yellow LED lights up.
I noticed on YouTube (https://www.youtube.com/watch?v=owvgzOeLOo0 at 2:30) that another reader of the book needed a 2N2222 transistor to amplify to signal from the 555 timer. I had no such problem.
I made a short video of this experiment. You can find it on YouTube at: https://www.youtube.com/watch?v=ZIwcqI1z7N0
The yellow arrows indicate the wires from the hashtag on the keypad and the output of the 555 timer to the relay. |
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