Small RS232 to TTL converter

RS232 to TTL converter.

This is a small and compact RS232 to TTL level converter that I use to connect a computer or calculator running terminal emulation software to some devices with 5V compatible serial ports. I like to use it with my HP49G running dTerm v1.1 by James D. Purdy (thanks a lot!).

This circuit is based on the very common and simplest MAX232 so it requires 1uF capacitors. Luckily I had at hand all the necessary components in SMD packages to make this circuit fit in a DE9 connector backshell.

If you want to build a transistor based RS232 to TTL converter that does not use a MAX232, check the project Small LED dot matrix sign.

The finished PCB:

RS232 to TTL converter PCB.

It was necessary to cut the board very carefully as I used a phenolic board, which is so easy to break.

All SMDs soldered:

RS232 to TTL converter PCB with components.

The female DE-9 connector is soldered directly to the board:

RS232 to TTL converter PCB with its DE-9 connector soldered.

Fits nicely:

RS232 to TTL converter PCB fit.



Capacitors are short enough:

RS232 to TTL converter PCB profile.

With its cable and connector:

RS232 to TTL converter PCB with its cable.

Ready to go:

RS232 to TTL converter PCB fully finished.

Using it to configure an industrial controller with an HP-49G calculator:

RS232 to TTL industrial controller.



The schematics:

RS232 to TTL converter schematic.

The PCB (click for a larger version):


RS232 to TTL converter PCB layout.

The schematics and PCB were made with KiCAD EDA

Click here to download a 1:1 postscript version of the PCB layout.

You may use Ghostscript to view, convert or print this file.

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