Hello,
this is my earlier post, http://forum.allaboutcircuits.com/showthread.php?t=56394, with a "bump" warning. If a moderator wants to combine the two threads, please do.
Using KB817 optocouplers.
Please note I forgot to draw pull-up resistor on CD4049UB input, and on logic side output (which value is ideal?)
I was hoping to get some general input on my revised design. Some things I would like to point out:
- Driver chips powered from USB, only sharing common ground with parallel port.
- Now using CD4049/4050 inverters/buffers as driver chips to minimize load on PC parallel port, and also keeping polarity intact.
- Using separate power source from USB for powering LEDs on PC side, and thus be able to totally isolate both 5v and ground on either side of circuit.
- 1K series resistors on LEDs for If=4mA @ 5v (LED Vf=1.2V from KB817 optocoupler datasheet). CD4049/4050 has sink current of 3.2mA(min) to 6.4mA(typ) resulting in minimum Current Transfer Ratio of 110% in optocoupler.
There will be 9 outputs used from PC parallel port, so I'm well within USB 100mA limit (500mA is only when properly asked for in software?).
I am eager to take on this project again, hopefully you will have some additional good tips like last time!
Henrik
this is my earlier post, http://forum.allaboutcircuits.com/showthread.php?t=56394, with a "bump" warning. If a moderator wants to combine the two threads, please do.
Using KB817 optocouplers.
Please note I forgot to draw pull-up resistor on CD4049UB input, and on logic side output (which value is ideal?)
I was hoping to get some general input on my revised design. Some things I would like to point out:
- Driver chips powered from USB, only sharing common ground with parallel port.
- Now using CD4049/4050 inverters/buffers as driver chips to minimize load on PC parallel port, and also keeping polarity intact.
- Using separate power source from USB for powering LEDs on PC side, and thus be able to totally isolate both 5v and ground on either side of circuit.
- 1K series resistors on LEDs for If=4mA @ 5v (LED Vf=1.2V from KB817 optocoupler datasheet). CD4049/4050 has sink current of 3.2mA(min) to 6.4mA(typ) resulting in minimum Current Transfer Ratio of 110% in optocoupler.
There will be 9 outputs used from PC parallel port, so I'm well within USB 100mA limit (500mA is only when properly asked for in software?).
I am eager to take on this project again, hopefully you will have some additional good tips like last time!
Henrik