[sdiy] Protection Device?

[rsdio at audiobanshee.com]

The risk of relying on the PIC clamping diodes without also using the current limited resistor is that the PIC might actually power up when you don’t want it to if a customer attaches an input before applying the official power.

I consulted with a client who had a huge problem with this. The simple solution was to add a resistor as seen in all of the Microchip example circuits.

All in all, I agree that the op-amp conditioning of the input signal before it reaches the PIC pin is ideal. Then again, I never use the internal ADC for anything besides a simple pot reading, and even then I’m most likely to use an external ADC for better results.

Brian Willoughby


On Jun 19, 2018, at 4:29 PM, Tom Wiltshire wrote:
> The PIC does already have clamp diodes.
> 
> My original schematic for the Druid VCDO chip specified external protection diodes as discussed. When we (me in collaboration with Frequency Central) actually released DIY boards for this project, we didn’t include the protection diodes and upped the series protection resistor to 4K7. So far (5+ years? I don’t remember any more), we’ve never had a report of a dead module from an over-voltage input. So op-amps are one way and do have a number of notable benefits like Olivier said - scaling, mixing, and the ability to add a specific offset being chief amongst them. But a “simple” solution can at least be robust too, if not quite as sophisticated.
> 
> That said, I’d entirely recommend the op-amp solution for all the reasons given - scaling, mixing, an offset, and some filtering into the bargain. What’s not to like?!