DC Voltage Detection

In order to monitor voltage of a circuit without affecting the circuit being monitored, you need to use a high impedance voltage sensor.   An op-amp (voltage follower) will work, provided you select a low-noise, low-offset op-amp.   A digital multimeter set to measure DC voltage will typically have an input impedance of 10MΩ or greater (between probes).  

 

High Impedance 10 to 15 VDC Detection

 

Low Impedance 5 to 24 VDC Power Signal Detection

This custom FeatherWing detects the presence of a 5 to 24 VDC signal without adversely affecting the detected circuit.   It uses a 4N33 optocoupler/ optoisolator to detect the 5 to 24 VDC signal.   The resistor R1 on the FeatherWing is selected based on the voltage input range in order to create the minimum forward voltage of 1.25 V at the 4N33.  

   

 

Related Links

How to use Grove Voltage Divider

LMV3xx Low-Voltage Rail-to-Rail Output Operational Amplifiers

https://www.allaboutcircuits.com/technical-articles/beyond-the-dmm-components-and-circuits-for-measuring-current-and-voltage/

NI voltage, current, power measurement tutorial

Grove Voltage Divider (0.3 to 43 VDC)

 

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The information presented on this website is for the author's use only.   Use of this information by anyone other than the author is offered as guidelines and non-professional advice only.   No liability is assumed by the author or this web site.  

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