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I have a home automation project and am looking to use multiple current sensors (ACS712) for multiple appliances. I just need to know whether current is present or not instead of the current value. Is it possible, that I connect the ACS712 sensor to the digital input of Arduino, and get HIGH or LOW via digitalRead() function. If not, please suggest an alternative to detect ac current is present or not with digital input i.e. HIGH or LOW that can be read via the digitalRead() function.

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    This has already been asked on EE.SE. You will end up being asked the same questions here; if you don't help us then we cannot help you. Dec 7, 2015 at 19:08
  • The answers over at EE also suggest that this is not the most appropriate sensor for this purpose. Given you are detecting AC, note that the ACS712 returns values representing the sine-wave, crossing over at "0", which is 2.5v output from the sensor. So you could take samples via the Arduino over a short period and detect the peaks in software to determine the total current, but from the answers below and at EE it seems an alternative sensor component, or additional circuit between the ACS and the Arduino would make the most sense if you need to use this particular sensor.
    – Grant
    Jan 29, 2016 at 4:55
  • Please do not cross-post the same question on different Stack Exchange sites. See Is cross-posting a question on multiple Stack Exchange sites permitted if the question is on-topic for each site?
    – Nick Gammon
    Jan 29, 2016 at 5:28
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    I'm voting to close this question as off-topic because posting a question to multiple sites is explicitly prohibited. Jan 29, 2016 at 5:33

4 Answers 4

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Considering an ATMEGA with a 5V VCC we have:

LOW  = < 0.3*VCC = 0,3*5V = 1.5 V
HIGH = > 0.5*VCC = 0,5*5V = 2.5 V

You can connect directly to the Arduino if the output of your sensor is higher than 2.5 volts whether current is present or below 1.5 volts if not. This would translate to HIGH or LOW output from digitalRead() function respectively.

You need to recalculate this values for the 3 volt version of Arduino, probably in this case is better the comparator solution to ensure up to 3 volts max logic level.

Example circuit as follow, just need to set voltage divider to desired threshold (note this is for 5v case),

Comparator

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  • You should instead use the Peak Detector example from the datasheet; it's designed for AC use and is much more appropriate for a current/no-current output. Dec 7, 2015 at 19:10
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Use a comparator for an adjustable threshold and feed the output into the arduino digital pin.

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    Can you please expand your answer to include how to do this? What components would the OP need? Thanks! Dec 11, 2015 at 0:48
  • Your answer would be even more useful if you could include more detail. For example, can you suggest a comparator that would be suitable, or a link to a tutorial that does something similar.
    – dlu
    Dec 31, 2015 at 17:45
  • Depending on which Arduino, it already has an analog comparator.
    – Nick Gammon
    Jan 12, 2016 at 5:38
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It seems like you could do this with a transistor (if "faking" a digital signal from the ACS712 doesn't work). A simple circuit where the VIOUT of the ACS712 drives the base of a switching transistor connected to a digital pin on the Arduino with an internal pull up might do the trick (assuming that the ACS712 give you a voltage on VIOUT that is proportional to the current).

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The Arduino/AVR (for instance ATmega328p, chap. 22) has an analog comparator (D6/AIN0, D7/AIN1 or any analog pin). This could be used with the correct reference voltage.

Cheers!

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