Generic RS-232 solutions

LoopyByteloose

It seems that Maxim has overtaken the RS-232 world.

I cannot locate a simple DIY RS-232 schematic [noparse][[/noparse]like transistors and resistors].· I realize to do this properly I have to provide +12 and -12 volts, where as Maxim does it all in one chip, but the problem is that I just cannot locate a local outlet in Taiwan.·

I do have 3904 and 3906 transistors a plenty.

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G. Herzog in Taiwan

Forrest

Maxim isn't the only company that makes the MAX232 chip - I know TI makes them also. If you really want to use transistors - I'd check out the schematic for the BS2 OEM board which uses 2N3904 and 2N3906 transistors for a serial interface www.parallax.com/detail.asp?product_id=27290

kelvin james

This might help you out
chaokhun.kmitl.ac.th/~kswichit/ap275/ap275.htm
found on this site
www.commlinx.com.au/schematics.htm
Everthing here for schematics and more.

kelvin

LoopyByteloose

The BS@ OEM schematic produces +5/-5V by the addition of a certain chip. Since I must start to consider power supply, I figure that going to at least +9/-9V is better from the noise reduction and data dropout standpoint.

Kelvin pointed me to a site that lists tons of stuff, but all I find is the MAX-232 in cables or speicalized RS-232 applications. This is similar to my attempts at Google.

I suppost the BS2 schematic can be modified to high voltage supply swings, but I have to think about it. As I often smoke these first tries, I was hoping that there was just a tried and true generic solution.

Gunther provided an op-isolator solution, but it is powered by the RS-232 port through modification of the control lines in software. I am not sure how to do that, but I suppose that I could just try +9/-9 to those pins and all would be okay.

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G. Herzog in Taiwan

Guenther Daubach

Kramer,

+/- 9V should be fine for the transmitter. The receiver could even be simpler, just use a resistor with one end vonnected to the COM port's TxD line, with a diode to short the negative voltage, and a Zener to limit the positive voltage to +5V. Both cathodes go to the other end of the resistor, and the anodes go to ground.

For the opto isolator solution, you need to set the RTS and DTR lines to the required levels. In Visual Basic, for example, the MSComm control has the RTSEnable and DTREnable paroperties to do this.

BTW: STMicroelectronics also produces the level shifters, they call them ST232. I'm using here the ST3232 which is a version that can also be operated at 3 Volts.

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Greetings from Germany,

G

LoopyByteloose

I came across an IC - the LT1032 which is a quad RS-232 line driver that can be used for TX.· While it only outputs +5/-5 and requires +6/-6 supply, it does come in a low-power CMOS version for micropower applications.· The RX side can be configured as you suggest.

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G. Herzog in Taiwan