Test Instrumentation

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We can easily find many types of digital optocouplers but its very rare to see any analog optocoupler application especially in hobby electronics. Even though its very essential in many type of analog circuits especially in current and voltage monitoring/measuring circuits where input and output side should have isolation. If someone is measuring/monitoring the high DC voltages or current ,and its also driving inductive loads, then it can easily damage MCU or any other measuring hardware. To solve this sort of problems analog optocouplers are used.

Here I am sharing circuit of one of analog optocoupler using easily available components.




1 x HCNR200 or HCNR201

2 x LT1097 (or any other good op-amp)


1 x 2N3906 (or any other compatible PNP transistor)


1 x 1N4150 (or any other compatible diode)


2 x 10uF (optional)

4 x 0.1uF

1 x 47pF

1 x 33pF


1 x 50k pot

2 x 10k pot (optional)

1 x 200k ±1

1 x 174k ±1

1 x 33k

1 x 6.8k

1 x 2.2k

1 x 270R


Testing procedure

Apply ± 5/10/12/15V supply to both input and output side op-amps. It can work with wide range of dc supply but for that;

minimum supply voltage > (maximum input signal voltage + (op-amp supply - maximum op-amp output voltage for that supply))


For LT1097;

minimum supply voltage  > (maximum input signal voltage + 1.2V)

After applying separate power supply to both op-amps (for example ±15V) apply constant voltage (0≤ VIN ≤13.8) at VIN terminal. Now test the voltage at VOUT terminal the voltage should be equal to input voltage or use VR1 to make it equal to input. Similarly test it for different input voltages.


Circuit shown in FIG. 1 & 3 is unity gain circuit which mean output voltage will be equal to input voltage.

It only work with positive input voltages (VIN ≥ 0) regardless of single or dual supply of ap-amp.

All the resistors used in this circuit are with ±1% tolerance.

This circuit is also tested using lm741, lm358 dual op-amp IC and it worked well.



  • Low cost analog isolation
  • SMPS feedback loop, SMPS feedforward
  • Monitor motor supply voltage






Schematic of Precision analog opto-isolation amplifier using HCNR200/201

FIG. 1: Schematic


PCB design of Precision analog opto-isolation amplifier using HCNR200/201

FIG. 2: PCB Layout




Precision analog opto-isolation amplifier using HCNR200/201 Circuit

FIG. 3: Circuit Source (HCNR200/201 datasheet)

Circuit Testing and Demo videos: tinyMonster - Analog Precision opto-isolator