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Mark1960 · 29th Jun 2021, 11:00 pm

The pull up resistors could probably be increased to 100k as they are only used for a static signal level and don’t need to worry about input capacitance. 47k is probably a good choice, with 4k7 in series with each switch. Then the switches could pull the inputs down to 0.5 v.

There could still be an issue if the PIC is programmed incorrectly and the pins driven as outputs. 1k or 2k series resistors might work but I’m not sure if that would be high enough to protect the 8154.

29th Jun 2021, 11:00 pm	#21
Mark1960 Octode Join Date: Mar 2020 Location: Kitchener, Ontario, Canada Posts: 1,294	Re: Ortonview PCB The pull up resistors could probably be increased to 100k as they are only used for a static signal level and don’t need to worry about input capacitance. 47k is probably a good choice, with 4k7 in series with each switch. Then the switches could pull the inputs down to 0.5 v. There could still be an issue if the PIC is programmed incorrectly and the pins driven as outputs. 1k or 2k series resistors might work but I’m not sure if that would be high enough to protect the 8154.