1-Channel PC817 Optocoupler Isolation Module Optoelectronic Isolator Signal Isolation and Anti-Interference 3-5V 12V 24V (Pack of 2) (12V)

I bought 20 of these to interface a Nayex credit card reader to a car wash. The card reader would output a 5V signal and the car wash required pulling a 12 volt line to ground. To make it reliable, I had to replace the input resistor with a smaller value. I think it was a 1k and I replaced it with a 220 ohm resistor. The resistor value needed depends on the output current required. I expected I'd need to modify it when I bought it. It was easy to modify and all 20 of them have been working perfectly for a year now.

Works well - as described

They both worked as expected. The reason I gave only 4 stars is becasue the chip is a TLP785; not a PC817 as the mistakenly statr in thier product description.

I have no complains at all. The item is entirely as described.

The instructions are a bit confusing if you're not familiar with the terminology, but after figuring it out it's worked quite well!

it's not PC817 as advertised, but TLP785G, which is actually a slightly better part. The problem is in the choice of the input resistor: at 4.7 kOhm, it only allows ~2.2 mA at 12V, resulting in ~3.5 mA output current. This is plenty enough to drive an MCU input, but may not be enough for other loads, and far below the capability of the chip (60 mA max). The recommended input current for TLP78 is 16...25 mA, so the input resistor R1, which is 4.7k, should be considerably smaller, perhaps ~680 Ohms, if higher output current is needed. The seller would do their customers a favor clarifying this.

No issues with these

On 4V input there is 90+ Ohms resistance between GND and OUT, 8V has 38+ ohms and 13V has 29 ohms. This is very significant as I tried to switch LED array and they were not as bright as using relays as switch.