TTL 3.3v to RS232 +-12v?

In the ax500, I notice that whatever I\'m sending from my mbed microprocessors it doesn\'t echos back my commands. i think it\'s cause the voltage is not right to communicate with the controller. Do I need to build a voltage level shifter such as max232?


How do I get my 3.3v inputs into the serial port of the controller?

By the way, when I try to read the values from the controller in RC mode, instead of seeing numbers, I see lots of blackbox, sometimes smiley face.

The controller does not require the full +12/-12V of the true RS232. 0-5V is usually sufficient. But it does expect the signal to be inverted.

Also, the controller will emit a +12V/-12V signal. If your microcontroller input is TTL, this can cause damage to your board or to the controller output. You should at the very least have a resistor (1K) on the controller\'s output.

However, the correct way to do this is to add a MAX232 level converter.