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RS232 to TTL level converter

Perhaps this is the most famous RS232 to TTL level converter. When launched by MAXIM, it become so popular that several clones acquired as the years went by. This project shows how it is possible to implement a small module to interact easily with devices which support the asynchronous serial interface (TTL levels).


Modern computers don't have serial ports. They have USB (Universal Serial Bus) ports instead. In order to use this converter, you must install a PCI card to your motherboard (a rather expensive and risky solution if you are not an expert). A better and simpler way is to use a USB to serial converter. The circuit will work just fine with no problems.

  • Five 1F /16Volt electrolytic capacitors.
  • One MAX232 Chip (or a clone).
  • A 16 pin DIP socket (for the MAX2323 chip).
  • A female 9 pin DSUB connector (for PCB).
  • Female pin header (4 pins. If you have one with more pins, just cut it).
  • A small piece of a Veroboard
  • Wire for connections
  • Solder and soldering iron

Also you will need a stabilized 5 Volt external power supply. Normally, you get the necessary volts, from the external circuit you connect to the converter.

Schematic Diagram

Here is the schematic diagram of the RS232 to TTL level converter

Attention: If you have MAX232A or MAX220, then you must change the values of all capacitors in the schematic, according to MAXIM. In the following array you see the values of the capacitors needed for each chip.

Chip Capacitance (F)
  C1 C2 C3 C4 C5
MAX232 1 1 1 1 1
MAX232A 0.1 0.1 0.1 0.1 0.1
MAX220 4.7 4.7 4.7 4.7 4.7

*Note: Special care you must take when you connect the converter to the external circuit. You always connect the RXD line of the converter to the TXD line of the external circuit. Same thing with converter's TXD line. Connect it to the RXD line of the external circuit. The following picture shows this interconnection (e.g. with a microcontroller).


In the following pictures you see the converter, build on a small piece of Veroboard.


Here, you see how is connected with AVR board of Education

If you don't have any serial port to your computer, you can use a USB to serial converter. Here is an example picture.

Created: 16/07/2009
Updated: -

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