comparatormultisim
In the images below I have the same schematic in multisim, one snapshot for each state of the comparator. I've got the VCC pin connected to 12VDC and the ground and VEE pins to ground. There is a distinct difference between the two states, but 15.8 mV for a "high" doesn't seem right. Shouldn't it be VCC? What am I missing?
Note: I just realized that one of the voltage labels is over the pin, that's pin 8 that's covered.
The long leg of the LED was attached to the corresponding output pin with a 1kohm resistor in between. The short leg of the LED was attached to ground but the comparator GND pin was not. I expected the LED to light up when I flipped the power switch.
Seems to me that you have connected the Anode to the output of the comparator and the cathode to the GND, that can not work for an open collector/ open drain output , the way this works is that you have to connect the positive supply to the load (LED and resistor) and then the output of the comparator will provide the ground (sink current) to the load (LED Cathode)
If your Arduino is reading both states, 0 and 1, your comparator may be OK. The problem is your inputs. They should not be "~0.5 volts". Instead, try a circuit like this
simulate this circuit – Schematic created using CircuitLab
Best Answer
The LM311 has an open-collector output; when the output is high it's actually high-impedance. If you want a high voltage then you'll need to use a pullup on the output.