ljbeng wrote:
The LED flashes but pin 5 only drops to 1.6v and the processor does not see the pulse go low.
...
For now I have taken out the 1K and dropped the led. Does anyone see an easy substitution fix? Thanks.
The transistor output of the opto-coupler is
unable to drive this load. Options at this point
are to find a substitute opto-coupler with a
higher current transfer ratio, or boost the
opto-coupler's LED current by reducing the
3k3 ballast resistor. Other changes would
require a PCB change.
(1) Reduce the 3k3 to 1k0, to get 10mA of
LED current (you are at 3.18mA now).
(2) Try a
4N35 device and no other changes.