Can anyone tell me how I can read the resistance between pins 4 and 6 of the serial port using VB or c++?
guy40az 0 Junior Poster in Training
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Jump to PostThis looks like a fairly difficult task. How do you plan to calculate resistance using capacitance? I would suggest you create a wheatstone bridge setup like
Here is another …
Jump to Post> Can anyone tell me how I can read the resistance between pins 4 and 6 of the serial port
Serial ports are digital.
Try using the analog game port used for reading analog joystick positions.
Jump to PostMy electrical is rusty but i think t=RC will work. But I suggest you to do lots of research before proceeding with it. Pins from the serial port have physical voltages of their own. This is a fairly difficult problem and you may end up frying your port. You are …
All 9 Replies
tesuji 135 Master Poster
hi guy40az,
i am afraid this is not an easy task. Once i had programmed similar problems using plain c under real mode, what is rather outdated. Today i am using professional library for port and memory mapped IO on XP. Maybe you will succeed by using this interesting library: http://www.codeproject.com/KB/system/serial.aspx
good luck!
krs, cliff
guy40az 0 Junior Poster in Training
krs, cliff
Thanks for the link I think I can us the info to make it work.
I was also thinking about using a rc circuit and measure the time it takes to charge the capacitor and I could figure out the resistance that way.
hammerhead 19 Posting Whiz in Training
This looks like a fairly difficult task. How do you plan to calculate resistance using capacitance? I would suggest you create a wheatstone bridge setup like
Here is another link for serial port.
http://electrosofts.com/serial/index.html
guy40az 0 Junior Poster in Training
My plan was to calculate the resistance of the RC circuit. The formula T=R*C.
T=time
R=resistance
C=capacitance
So if I know the capacitance and the time it takes to charge the capacitor I can then calculate the resistance.
Do you think this would work?
Colin Mac 53 Posting Whiz
It won't work and you will probably fry the port. Why are you trying to do this?
Salem 5,265 Posting Sage
> Can anyone tell me how I can read the resistance between pins 4 and 6 of the serial port
Serial ports are digital.
Try using the analog game port used for reading analog joystick positions.
hammerhead 19 Posting Whiz in Training
My electrical is rusty but i think t=RC will work. But I suggest you to do lots of research before proceeding with it. Pins from the serial port have physical voltages of their own. This is a fairly difficult problem and you may end up frying your port. You are better off with a multimeter.
Serial port behaves erraticaly and produces +3 to +25 V for logic 1 and -3 to -25 for logic 0. I suggest you use a Max232 converter IC to scale them down to static +5V and 0V.
Colin Mac 53 Posting Whiz
It won't work. The serial port has a maximum output current and will try to charge the cap with an unlimited amount of current.
We still don't know why he wants to do this.
hammerhead 19 Posting Whiz in Training
Once the capacitor get charged it will start acting as an open switch. Even I am curious as to why the op wants to do such a thing.
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