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:
It was necessary to cut the board very carefully as I used a phenolic board, which is so easy to break.
All SMDs soldered:
The female DE-9 connector is soldered directly to the board:
Capacitors are short enough:
With its cable and connector:
Ready to go:
Using it to configure an industrial controller with an HP-49G calculator:
The PCB (click for a larger version):
The schematics and PCB were made with KiCAD EDA
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