Ok, that makes sense. So, when the sensors are in an 'open' state, they are drawing no voltage allowing that voltage to flow to the AND gate.

So, once a sensor is tripped 'closing' the circuit, the voltage is diverted to ground pulling the voltage away from the AND gate?

Thanks again.

 

Ever been in the shower when someone flushes the toilet?

Living alone now, that problem is over.

Wondering if trying to fit new electronics to those "unrepairable" ones could be part of this project? Now that I think of it I have one just atop of my fridge doing nothing.

 

Ok, that makes sense. So, when the sensors are in an 'open' state, they are drawing no voltage allowing that voltage to flow to the AND gate.

So, once a sensor is tripped 'closing' the circuit, the voltage is diverted to ground pulling the voltage away from the AND gate?

You are correct. Try this:

Connect one end of a 10kΩ resistor to Vcc.

1. Connect the other end to one end of a switch.
2. Connect the other end of the switch to GND.
3. Take a voltmeter and connect the black probe to GND.
4. Connect the red probe to the resistor end connected to the switch.

When the switch is open, the voltage on the meter will be Vcc. The resistor is acting as a pull-up, that is, when the switch is open, the AND gate sees Vcc. In this way, we ensure the AND gate knows the switch is open, otherwise you'll get random behavior from the circuit.

When the switch is closed, it will be 0V. The AND gate sees 0V because the closed switch has next to no resistance (vs. the 10kΩ resistance between it and Vcc) - path of least resistance.

The resistor is also preventing a direct short between Vcc and GND when the switch is closed.

 

Ahhhh......starting to make sense now. Thanks a lot elec_mech, I have read about 'pull-up' resistors before but it never really clicked. It is making sense now. I will bust out the multimeter and do some tests.

Thanks again for all your help.

 

Wondering if trying to fit new electronics to those "unrepairable" ones could be part of this project? Now that I think of it I have one just atop of my fridge doing nothing.

Great idea. A small PIC or AVR, even a simple to use PICAXE would do nicely. I kinda wish mine was on the fritz. It'd make a great project.