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Old 5th Apr 2019, 5:15 am   #19
TonyDuell
Dekatron
 
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,190
Default Re: Mk14 programming

The PC TxD line will swing -ve -- in fact it will be negative (-12V on many machines) most of the time. So shouldn't you add an inverse-parallel diode to the LEDs in the 'to MK14' section (the red indicator LED and the optoisolator) to protect them against reverse bias?

I also wonder (without trying it) if you could connect the red indicator LED in series with the optoisolator LED and have one series resistor and inverse-parallel diode.
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