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Arduino MAX232

The Maxim MAX232 is a very handy device. These are a few circuits that demonstrate how to connect a MAX232 to an Arduino, or any ATmega or ATtiny chip. There is even one used as a power supply.

MAX232 Datasheet

The MAX232 Datasheet from Maxim

MAX232 Arduino

This is a modification of the schematic for the RS232 serial loader to show how to hook a MAX232 to an Arduino. It is not a shield - just a little kludge board that can be added to any microcontroller. You can put the MAX232 on several of the available shields, some of which have small breadboarding areas.

MAX232 Arduino schematic.

A minimal Arduino MAX232 circuit consists of a the device and four capacitors. It can be connected to the serial port in several ways, though. Shown are a MAX232 connected as a DCE and a DTE, using RTS/CTS handshake. The RS232 pinouts shown are for the 9-pin DB9 standard connector.

MAX232 schematic DCE and DTE shown with RTS/CTS handshake.

You can also use the Arduino MAX232 as a +/-10V power supply, as seen in the schematic below.

MAX232 as a dual output +/-10V power supply.

How can you drive an ultrasonic transmitter from a 5V supply? You can use a MAX232 to generate a signal by driving both TTL inputs and hooking an ultrasonic transmitter to the outputs. The MAX232 generates it's own +/-10V supply, and by bridging the outputs you can double the effective voltage. Both outputs driven lowers the output to +/-8V, so bridged, you get around 16Vpp.

MAX232 ultrasonic transmitter, TL084 ultrasonic receiver circuit.

When it is idle, you keep both inputs, SIG+ and SIG-, either high or low. To transmit, first toggle one input to get the two in opposite phase, then continue by toggling both inputs at the same time. Make sure you do this at the operating frequency of the transmitter. The transmitter appears similar to a long cable (2000pf) at the design frequency. When you're done, set both inputs to the same phase again. When you're not hammering the transmitter, the +/-10V is available for other things, too.

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