Measuring voltage output of Serial/LPT port

[Kasamiko]

I need a simple setup to measure the voltage being put out by my serial and parallel port..
any suggestions? ???

rhonn

 

[ante1]

Hi Rhonn,

The voltage put out by the ports can be viewed on an oscilloscope or measured with a multi-meter.

 

[Kasamiko]

Nice to hear from you again Ante.. ;D Yes I like to do that, but my digital tester can't simply lock on it..maybe I needs some diodes and caps on particular pins to measure it out..

rhonn

 

[ante1]

Rhonn,

Don't you have a scope?
I

 

[Kasamiko]

Hi Ante
Just want to "STEAL" some power from my serial/parallel port to power some interface using MAX232/MAX3232..


rhonn

 

[ante1]

Hi Rhonn,

You should avoid messing with the ports like that; it can cost you the motherboard. Just get 5 or 12Volts inside from a free device power connector its much safer. Don

 

[MP1]

Rhonn,
Is this what you are looking for? I would not try for more than 5 mA.

MP

View attachment 36007

 

[ante1]

MP,

The MAX232 alone consumes >=5mA at idle so this is not safe to do I think.

 

[MP1]

No, I would not use the MAX232. Use the DS275. This is the one that I use for my battery powered micro devices. Much nicer on batteries, too.

MP

 

[ante1]

MP,

You are correct, that

View attachment 36090

 

[MP1]

Much nicer to connect and very easy on batteries if you are powering from one. There is also a MAXxxx number which does not use the caps. It is MAX233, if looking to get away from the caps.

Rhonn, maybe you can ask for some free samples of these other chips as well.

I have attached the data sheet for the DS275 for anyone interested in it.

MP

DS275_Data_Sheet.pdf

 

[surajbarkale]

I found a good discussion here -
http://www.epanorama.net/circuits/rspower.html

 

[Kasamiko]

Things are getting complicated ;D Just to be safe..I'll used an external power source.. 8)
Thanks to all

rhonn