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D25 printer port advice!

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epilot

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Hello,

I have built an AVR programmer to program my ATMEGA16 and ATMEGA32 in C language.
the programmer uses a printer port(D25) and 5 wires which are connected to the microcontroller to programms the AVR.
unfortunately I have to use a 7805 and an external power supply for the microcontroller during the programming time.
I am not familiar with printer port, so can anyone suggest me a pin on the printer port which I could use it as a VCC for the 7805 to omit the external power supply?

thanks for any help
 
This would lead you into reliability problems, not all parallel ports are capable of supplying 5v outputs, although they are supposed to be. You would be better off stealing the power from the USB bus with an additional lead.
 
tunedwolf said:
This would lead you into reliability problems, not all parallel ports are capable of supplying 5v outputs, although they are supposed to be. You would be better off stealing the power from the USB bus with an additional lead.

I said that I can use my 7805 with the programmer so I don't need a 5V from the printer port, every voltage more than 7V is ok.

Do you want to say that there is not any voltage more than 5V on the printer port?
 
The Printer(Parallel) port was traditionally at TTL levels. I think you are confusing the Parallel port levels with the Serial (Com) port levels, which are significantly higher.

However, some of the modern motherboard implementations of a Parallel port seem to wander down to as low as 3.8V in some cases. The high output on a parallel port pin will not source sufficient current to power your programmer. All that will happen is you will fry the port on the PC, both quickly and silently.

If you canabalise an old USB lead, isolate the data +/- (Green & White) lines and use only the V+ and Gnd (Red & Black) lines to power your circuit then you don't need the 5V regulator, but merely some decoupling. You could also steal the power from the Keyboard port if you so wished, it's easier to just use an old USB lead because of the ready availability of a socket on the PC.
 
Yes, the printer port has no power connection, you can parallel unused pins (with diodes) and set them high, but it's only TTl levels, and the diodes drop 0.7V as well. Use an external supply!.
 
If your computer has a USB port you can use the +5v supply of the USB port to power your programmer instead of using external power supply and 7805 requlator
 
Hey I have found that my printer port does not work with the AVR programmer while it works and programs the AVR with 2 other PC's!
is it fried? if so what can I do?
can I repair it?
perhaps the singals of my printer port are weak? Perhaps I should use a buffer
IC for my programmer?
 
Try it on a printer....if it works on the printer, the port is probably ok...
though not all printers use every line from the parallel port.

I wouldn't even consider connecting anything to a parallel port without buffering, but if your port is ok, i.e works with the printer, then yes fix your programmer so it will work properly with most parallel ports.
 
It's VERY easy to damage the printer port, which as it's usually part of the motherboard isn't a very a good thing! - as Tunedwolf suggested, it's always advisable to buffer the port, and VERY important to only plug and unplug with the computer turned OFF.
 
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