converting rs-232 voltage to current in my circuit design 1

[agent38]

Im using a TI Transimpedance Amplifier OPA138 in a design. The amp is used to convert input current to voltage output.

For reasons related to quick testing capabilities I want to take rs232 voltage signals (from my laptop) and input these signals into the amp. But the amp like I said before is looking for current (10mA max).

So my question is since the serial signal is voltage based can i just place a series resistor between the rs232 signal source and my amp to provide the current that the am is looking for?

I calculated 5k resistor foe 2ma current input. I measured 10V serial voltage.

 

[MikeHalloran]

A valid RS232 voltage signal can go from 3-ish to 13-ish volts, either positive or negative, depending on whether a space or a mark is being asserted. Can your TA accept a current signal of either polarity?

If you are only looking at a PC's sorta- pseudo- RS232 output, it may swing 0 to 5 volts or 0 to `12 volts depending on how it was mis-engineered and by whom.

To sort of half answer your question, a series resistor as you have proposed should limit the current going through your current transducer.


Mike Halloran
Pembroke Pines, FL, USA

 

[agent38]

I measured the serial signal on an oscilloscope. I measured 10v. Yes the TA can accept +/- 10mA max

 

[OperaHouse]

Just to be sure. Are you trying to convert serial voltage to serial current or to a linear voltage that represents serial data?