It is true that it could be fatal if one would directly connect a circuit, with an external power source, to the parallel port of the PC. There will be no inputs that will go back to the PC's parallel port yet there aren't aven diodes to protect the PC from feedback. The parallel port will be driving a DC Motor, a Stepper Motor, an Electromagnet and a flashing LED

thanks

 

Off the top of my head? I would say no. I would say you might want to protect your PC by isolating the parallel port form something that can make an inductive spike like 3 of your major loads, however.

 

Depending on your load, it can be fatal to you or another people that touches the PC

If the external power source and the PC have a common ground connection, the power supply should be isolated from the mains (ie it must have a transformer)

If you must control something that is not isolated from the mains you should use optoisolators between the PC and your load.


As dknguyen posted, only one of your loads (the led) is "safe" for your PC.

Both motors and the electromagnet should have, at least, diodes in parallel to protect the port from the EMF spikes they generate.

Without the diodes they "can be fatal" to the PC.

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E Cerfoglio
Buenos Aires
Argentina

 

You can't drive a stepper motor from the parallel port! The data on it are just voltages (5V) with low current.

You can however control drivers with those signals. Use opto-isolators for each wire connected to the parallel port. It's the safest way not to kill your PC.

The same way you can use status lines like PE (paper empty), busy and strobe for inputs to the parallel port.

Bosco

 

Quick word of warning! - it's VERY easy to kill the parallel port in your PC, and as they are now part of the motherboard, it's not cheap to repair it (adding an extra card may not be possible, and may not work for everything either).

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