What is the purpose of the 74HC04 inverter ?Typically your indicator leds would be on the ULN2803As outputs...
What is the purpose of the 74HC04 inverter ?
Starting to think that this push-pull I/O expander would have been a better fit, possibly no need for 74HC04.
And I'd recommend using 74HC14's because schmitt-triggers are so useful to have in stock, why get invertersthat aren't schmitt-triggers? (Well perhaps because they might be a little faster I suppose).
Hmm ... I was thinking the inverter was there to prevent all relays being energized during startup since by default the expander will initialize all I/Os to inputs with a weak pullup current to Vcc.
Interesting.. I am not familiar with this one. What is the advantage in this case?
What am I missing?
The PCF8574 can drive 30 uA (IOH) minimal, the input current of the HC04 is 1 uA maximum; (II) you can drive 30 HC04 inputs from one PCF8574 output. And it gets even better if you base the calculation on IOH = 100 uA