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The CYBOT RF Remote control
Part 4 - Building the Handset Stage 2
SCHEMATIC OF HANDSET
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As mentioned before, I have re-used the spare components from the stripping of the alarm.
You will notice that the bottom diode is a zener diode.
This is normally used in voltage regulation, limitimg and protection circuits.
Here,we're wasting it really, using it in it's forward mode as a standard diode.
This is due to a lack of diodes from the spares pile.
Basically, the circuit is nothing more than OR gates constructed from diode/resistor logic.
Touching any input terminal will energise the encoder.
This is done by a diode from each input commoned together to output Vdd to the encoder
The rest of the components simply place high / low logic patterns on the data pins (p10 - p13).
You will notice that only two outputs, Right Reverse and Right Forward have 39K pull down resistors
This is because pins 10 and 11 of the encoder have 15K pull down resistors on the keyfob board.