RS232 Booster

RS232 ports of modern laptops are not always complying with the original RS232 standard. If RS232 levels are expected to be +/- 12 volts, most of the time laptops RS232 ports produce in fact +/- 5 volts levels. For most peripherals, this is not an issue and they are responding as expected.

But some other will not act on a stable manner or not act at all. This is because they are expecting the original RS232 levels. One example of this problem is the use of a SKYSENSOR PC (Telescope controler) with a laptop.

There is a simple way to boost the RS232 weak levels, based on one of the most common RS232 IC (MAX232).

As this IC is able to convert RS232 levels to TTL and vice-versa, why not just input weak RS232 levels, convert them in TTL and reconvert them in correct RS232 signal. This is possible with a single MAX232 as it includes 2 full duplex converters that we will connect through pin9-11 and pin 10-12.

All you need is 4 caps, one IC and 2 connectors. If you want to add a small regulator on the board (already foreseen on the PCB) you just need to add a 78L05 regulator and a cap.

If you do not need to regulate the power supply, you can just replace the 78L05 by a strap (pin1 to pin 3) and drop the 78L05, C1 and C2

Schematic



All Files and Prints (ZIP file)

Board Print for TCI3 (see How To concerning PCB design to get and use TCI freeware)






C3-C4-C5-C6 : 10uF 16V IC1 : 78L05 (If regulated power supply needed) C1 : 100nf (If regulated power supply needed) IC2 : MAX232 C2 : 100uF 25v (If regulated power supply needed) DB9 Female and DB9 Male

contributed by Olivier de Broqueville.