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I'm attempting to connect to Loconet spec to a PIC32, and I've found a circuit to connect to an Arduino, but I'm not sure what exactly it does:. Specifically, I don't know what the LMN voltage comparator at the top middle of the schematic does. I think that what is going on is that the LMN is clamping the voltage to a certain level, between 0 and 5V or so in order for a microcontroller to read it as either a 0 or 1. I've seen another circuit that is similar, but uses an opto-isolator after the voltage comparator to actually interface with the microcontroller, which I'm assuming will then drop the voltage down to CMOS levels if it isn't already.

The inverting input pin 6 to the comparator is a voltage reference of 3V. This is what you are comparing the non-inverting input pin 5 to. When the non-inverting input is greater than the inverting input, the output pin 7 will be high. Notice that there is a feedback resistor from the non-inverting input to the output. This is for hysteresis. It will keep the voltage at the non-inverting pin slightly higher when the output is high, and keep the voltage slightly lower when the output is low.

This will prevent the output from toggling when both inputs are at very similar voltage levels. The 'output' is a connection to the collector of an internal NPN transistor that has its emitter connected internally to 0V through pin 4. The 47K will also protect the comparator from any inrush currents. The K 'feedback' resistor prevents the comparator from oscillating if the LocoNet signals do not have sharp transistions, effectively 'cleaning up' the copied signal.

There are 2 comparators in the LM package, the second one should be shut down by tying both its inputs to 0V if it is not used. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. What does this LMN circuit do? Ask Question. Asked 6 years, 6 months ago. Active 6 years, 1 month ago. Viewed 3k times.

So the output can still be randomly switching on and off if the input offset voltage should happen to be less than the input noise voltage. This is not really a good thing to do with an op amp, especially if it isn't rail to rail. Active Oldest Votes. This is basically what a schmitt trigger does. It gives you a nice digital output for your microcontroller. Bonus: There are two comparators on the LMN. One is simply not used.

The calculation that I did gave me 2. You must have switched the resistors around. I was treating R3 and R2 as a series circuit, which would give me 2. Bruce Gennette Bruce Gennette 11 1 1 bronze badge. Sign up or log in Sign up using Google.

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LM393N - LM393 Low Offset Dual Comparator



LM393N - LM393 Low Offset Dual Comparator


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