and right, if I think of it as a switch I guess it does make sense. When the LM311 is OFF then the output is floating and we just connect it to the pullup resistor causing it to go to 5v (we now have 5v on the input pin of the PIC).
If the LM311 is ON then the output acts like a ground and will pull the input of the PIC low.
I see. Then I guess the 'switch' has to be pushed when the inverting input is bigger than the non-inverting input. Because that's when we want our PIC input to go low. When the switch is NOT pushed I guess its floating, and thats when the non-inverting input is bigger than the inverting one?
My confusion comes from not knowing how the output of the op-amp can be floating. From what I know its 0v when inverting input is higher than the non inverting one and 5v when it's the other way around.
It has nothing to do with the opamp and inverting inputs and non inverting inputs..........it is entirly what the picaxe sees on its input that is the matter here, the picaxe dont give a **** what the opamp do, but only cares about what the input pin of the picaxe receives as a signal on its own input.
I know that the input on the PIC is high normally unless something pulls it low. (Because of the pullup resistor and the V+). Now the thing that will force it to go low is the switch when it's pressed. So what is the op-amp doing when the switch is pressed?
Okay, I was thinking of just ordering the PCB from ExpressPCB but it seems like I can only chose to have two boards made instead of just one?
I would like to build it myself, but it does seem to be a lot of hassle. I need to buy a drill and I dont actually have a laser printer either so I guess I need to find one (in a library maybe?)
I see that Input 3 has no pull-down resistor. That means the input will be floating, with possibly undesirable results, when the push-switch contacts open.
1. How do you know the values of the resistors?
2. I will be ordering the PCB instead of making it (dont have enough money to buy a drill etc) where would be cheapest to make it (I live in the UK).