Quote Originally Posted by Kitwn View Post
Not measured on a specific opto, but it is the measured output voltage of the proximity sensor when triggered. Opto outputs will vary depending on device and load current but with only 0.6V to play with I'm not chancing it. I was surprised at the low trigger voltage, but it's what I measured on the board input and the chip spec says it can be as low as 0.7V
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This is likely to be a problem with any board that only uses 5V logic on it's inputs. I assume the more expensive boards are more sophisticated. They'd better be for the difference in price.
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I'm happy that the 10K pull-up on the board will work OK with the single pole relays. The relay will isolate the actual board input from any noise on the wiring from the sensors and the overall noise level is going to be significantly reduced by my improvements to the wiring overall.
It's a shame they've used a 74HCT14 for the buffer on your BOB, the old (and now probably uncommon) 40106 hex Schmitt buffer was a better chip for such purposes IMHO, as the threshold voltages are more or less equispaced around 1/2 the supply voltage, something like 2.3V & 2.7V.