Completely stuck, please help!!!!

https://www.circuitlab.com/circuit/n92cn5/car-door-sensor/ This is my circuit, th light is supposed to turn on when any switch is changed but i cant seem to get the right voltages

by fergusryan
November 25, 2015

I don't get why you have any logic circuits in this at all. I think you should write out you truth table first of all.

by Garrett
November 28, 2015

@fergusryan,

Your simulation does not work for the same reasons that a very similar sim in this post did not work:

https://www.circuitlab.com/forums/basic-electronics/topic/66c5v8k8/strange-voltage-results-in-my-one-bit-adder/

so you may find the reply there helpful.

by signality
November 28, 2015

Also, your SPDT switch connections make no sense. In one position, they short the inverter gate outputs to their inputs.

Since the inputs are connected to 5V, the outputs will be at 0V so connecting them to 5V will cause the outputs to draw lots of current from the 5V supply.

With the CL gate models, this current will be about 0.5A per inverter:

https://www.circuitlab.com/docs/circuit-elements/#digital

In a real device this current would be somewhat lower but it would still be enough to at least cause them to get hot.

It may destroy them.

Doing that to all the outputs in a Hex Inverter chip would almost certainly destroy it.

by signality
December 01, 2015

If you want to turn on the light when any door is opened, then just put the switches in parallel to turn on the light. No logic needed.

If you are looking to turn on the light based on a change of state of the doors (when they open or close) you can't use static logic for that since you are trying to change the state of the light based on an edge. You will need an edge triggered flip flop for that.

Also, Is this comment seeking to understand why the circuit doesn't do what you want it to do, or why the simulation doesn't work the way you think it should work?

by Shandor
December 04, 2015

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