Column: Optical isolation


and 2, with Figure 4 showing the PCB. Circuit calibration is carried out with S1 to +5.00V


open: set VIN to +5.00V and VOUT by adjusting P1.


Module 2 Figures 5, 6 and 7 show the optically- isolated analogue input module 2, with its connections to the ADC port of a 5V microcontroller. Te circuit is also PUPIA1-based, with a high-linearity analogue optocoupler (HCNR201) providing photovoltaic isolation. Module 2 operates exactly the same way


as module 1, using the same components, but with R5, D4 (10V zener diode) and C5 added, which provide 10.00V reference voltage from a +12V power supply. Te 10.00V reference is then divided with R6 and R7 to obtain +6.26V. Tis reference voltage is then connected to the non- inverting input of buffer amplifier LM358P- 2B, with output fixed at +6.26V and sourcing to 20mA. For proper operation ensure that R7/(R6+R7) = 62.62%.


Figure 2: Module 1’s connections to an MCU


Figure 3: VOUT


vs. VIN


for modules 1 and 2


Figure 4: Module 1’s PCB


Figure 5: Module 2 www.electronicsworld.co.uk September 2022 15


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