Title says it all: can an opto-isolated input be analog or are they intrinsically digital?
Why: I am looking to purchase a relay control board and am deciding between a few options.
Here is my primary option, however I need 5 analog inputs and this one states that it has opto-isolated inputs. Could those be analog?
EDIT: Page 6 of the user manual has each opto-isolated line connected to a digital and an analog input pin. Does this mean it can accept analog (voltage) inputs?
Answer
It comes with full schematic. That could enable a little bit of hacking.
If I'm reading the schematic correctly, the opto-coupled inputs are connected to PC1/ADC1, PC2/ADC2, PC3/ADC3 on the ATMega. If U9, which is the opto-coupler IC, is removed then the ADC lines can be connected directly to the outside connectors. That would create 3 straight analog inputs.
Yes, an analog input can be opto-isolated. This is usually done with specialized opto-couplers, such as LOC series.
(source: IXYS application note AN-107)
These types of circuits aren't neatly as common as digital opto-couplers, though.
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