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Topic: Comparators (Read 1 time) previous topic - next topic


What are comparators?


There are google and wiki. 8)
In short comparators are device to compare


Two types digital and analogue.
1) Digital two groups of four bits input. When the binary value is the same on both the equals output goes high. There is also a greater than and less than output, these can be cascaded to any width you want.
2) Analogie or voltage comparator, two inputs if the + one is higher than the - one the output is high otherwise it is low.


Like Grumpy_Mike said. The digital type and the analogue type. I don't know what type you want to know, but if you mean analogue... Well it basically two Voltage divider and one op-amp.   

Here is example:  +5 V -- 10 K ---to "plus" side of op-amp ---- 10 K -- GND  <--- V1 is 2.5 V
                         +5 V  -- 47 K --- to "minus" side of op-amp --- 10 K  --- GND <--- V2 is 0.877 V
  The op-amp output will be a HIGH or + 5 V  <--- hope I am right.

Use a LM339  <----- It will work.  BUT do not use the following... LM741, LF071, LF072, LM1458 ... they did not works. I try. My raison is they need  dual power ( plus / GND / minus ). The LM339 do not need dual power only one. ( plus / GND )

Analogue comparator are usefull if you need two state ( HIGH or LOW ) 


Above is the internal circuit of the LM339. I want to compare 2 inputs, I will put the Higher Voltage on +Input 1 and the Lower Voltage on -Input 1. Do I need to connect VCC and Ground to 5V and GND from the Arduino? The Output 1 will be HIGH, right?


Do I need to connect VCC and Ground to 5V and GND from the Arduino?


The Output 1 will be HIGH, right?

Yes BUT this has an open collector output, that means you have to have a pull up resistor from the output to the +5. This can either be a real resistor (about 3K3) or the internal pull resistors in the arduino. (enable them with a digitalWrite HIGH once you have defined the pin as an input)

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