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[SOLVED] TTL signal to parallel port status pins

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hmalissa

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I need to read a TTL signal on the PC through the parallel port, and I'm thinking of using one of the status pins (10, 11, 12, 13, or 15).
In particular, the signal is the "output" pin of a LM555, and according to the specifications, it is around 3.3V when high when the LM555 supply voltage is 5V.
Can I connect the the LM555 output directly to pin 10, 11, 12, 13, or 15 of the parallel port? And, if not, what would be the proper way to read the TTL signal through the parallel port?
Thanks a lot.
 

IanP

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I need to read a TTL signal on the PC through the parallel port, and I'm thinking of using one of the status pins (10, 11, 12, 13, or 15).
In particular, the signal is the "output" pin of a LM555, and according to the specifications, it is around 3.3V when high when the LM555 supply voltage is 5V.
Can I connect the the LM555 output directly to pin 10, 11, 12, 13, or 15 of the parallel port? And, if not, what would be the proper way to read the TTL signal through the parallel port?
Thanks a lot.
Instead of direct connection (if something goes wrong ...) use an optocoupler, as shown on the attached picture ..
http://www.pyenet.co.nz/parallel-port-interface/
:wink:
IanP
 

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hmalissa

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Instead of direct connection (if something goes wrong ...) use an optocoupler, as shown on the attached picture ..
http://www.pyenet.co.nz/parallel-port-interface/
:wink:
IanP
Thank you very much for your reply, that is very helpful and exactly what I need.
I have 2 questions:
1.) Do I understand correctly: the purpose of the USB port is only to supply +5V (and ground) to the optocoupler output stage, right? So basically any 5V source would do, is that correct?
2.) I have already ordered the optocouplers, but I'd like to test my circuit before I get them. When I run a test with the timer output directly connected to the parallel port pins, do I need the 3.3k pull-up resistors too?
 

IanP

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Thank you very much for your reply, that is very helpful and exactly what I need.
I have 2 questions:
1.) Do I understand correctly: the purpose of the USB port is only to supply +5V (and ground) to the optocoupler output stage, right? So basically any 5V source would do, is that correct?
2.) I have already ordered the optocouplers, but I'd like to test my circuit before I get them. When I run a test with the timer output directly connected to the parallel port pins, do I need the 3.3k pull-up resistors too?
1=Yes
2=The timer's output does no require any pull-up resistor, it sources current from Vcc and sinks current to GND ...
If you have 5.1V zener, connect it between PPpin and GND, just for protection of the motherboard###
:wink:
IanP
 
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