[sdiy] Rotary Switch -> illuminated PB w/ multicolor LED?

Brian Willoughby brianw at audiobanshee.com
Fri Feb 18 01:42:39 CET 2022

On Feb 17, 2022, at 15:37, Tom Wiltshire wrote:
> I can only answer point (B) since I've tried Roman's technique of saving to EEPROM on power-down:
> Microchip give a supply voltage range of 1.8V to 5.5V or 2.3V to 5.5V for many of their recent chips. So "low voltage" is "below 2.3V". If we're operating at 5V normally, that gives us oodles of voltage drop and time before we've even close to the edges of the specification. We could lose a volt and a half and we'd still have another volt and a half to go before we even got close to "out of spec". While I understand your reticence to use an apparently unorthodox technique, in reality to program a few settings as the power drops is not doing anything that's pushing the limits in any way. If it was a critical application where people might die if it didn't work correctly, then ok - it's probably a no-no. But we're talking about state-saving on a synth module. The worse-case scenario here is that our poor user might lose some element of a patch. It's not the end of the world, so we can safely risk it for the convenience and extended memory life it offers.

I recall that the wide supply range is for the CPU, not necessarily its internal Flash programmer. Plus, there are restrictions that the maximum clock rate falls with the voltage, so you can't run at top speed with only 1.8V ... I'm sure there could be variation between PIC models, but I've worked with three or four and they don't support all features at low voltage.

> On another note entirely - Microchip want you to buy a $300 programmer because they claim the $30 one won't do the same job? Conflict of interests much?!?

The $30 PICkit is for developing firmware. It can also program. It wouldn't cost $30 if it was designed to be the most reliable programmer for end-user customers. Power comes entirely from a USB Host that Microchip has no control over, and they don't spend the money on boosting and regulating the 5V to any high quality.

The $300 ICE is for production lines. It's sole purpose is to program devices that are intended to be sold to consumers. Considering the costs of typical manufacturing equipment, $300 is already incredibly cheap.


p.s. Hey, you guys can cut all the corners you want. Just remember that there are limits due to the laws of physics.

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