# Connect Arduino to RS232

The device (a VC0706 Powered camera), incomporates a MAX3232 to convert to RS-232.

Unfortunatly, I don't have the tools or dexterity to remove the TTL/RS232 conversion manually.

My question is: is it possible to establish communication between the device and the Arduino with RS232 interface?

• Can you open it up to do some soldering? You could cut the tracks to the max3232 and connect directly to the camera module – geometrikal Jan 4 '14 at 1:07
• well it's too small for me to cut it with the tools that I have.. that's why I can't remove it manually – Majid Laissi Jan 4 '14 at 1:16
• One of these should do it sparkfun.com/products/449 – geometrikal Jan 4 '14 at 1:18
• @geometrikal is it really necessary? it says that it converts the RS-232 voltage to +5V. I don't need that as my RS-232 is already +5V (because it's powered by the arduino itself). – Majid Laissi Jan 4 '14 at 1:24
• @geometrikal according to sparkfun.com/products/133 it's possible. Now that I don't need a voltage conversion, I think the schematics should be much simpler. Right? – Majid Laissi Jan 4 '14 at 1:34

I think you are confused about the voltage level used to power the camera and the voltages used to communicate with the camera. The fact that the camera is powered with +5V from the Arduino is really irrelevant in this case.

If the camera has a true RS-232 interface then a logic 1 is represented by a voltage more negative than -3V and a logic 0 is represented by a voltage more positive than +3V. It sounds like the Arduino does not have a true RS-232 interface but rather uses conventional logic signals with a serial interface, and in this case a logic 1 is a voltage of about +5V and a logic 0 is represented by a voltage close to ground. An interface like this is sometimes called a "TTL serial" interface for historical reasons.

Note that these two interfaces are not electrically compatible. Connecting an RS-232 interface TX line to a TTL RX line may damage the receiver. You cannot solve this problem in software.

You have two options, as others have mentioned. You can remove the RS-232 voltage converter in the camera, effectively making it have a TTL serial interface, or you can add an RS-232 voltage converter to the Arduino.

If you mean connecting the AVR pins directly to a MAX3232 found at the camera side then you should avoid it because the (MAX3232) Tx pins transmits signals in a range of +5.5v to -5.5V that are not safe for the AVR.

Just use a max3232 in the AVR side too.

• Actually the only available pins I have are the NTSC Video, NTSC GND, TX, RX, GND and 5V. The MAX3232 is too small for me to connect anything to it (or even replace it with direct wires). – Majid Laissi Jan 4 '14 at 1:19
• @MajidL I meant that you should add a max3232 chip to the AVR pins and connect the outputs of that to the inputs of the max3232 at the camera side. You can get a board like this – alexan_e Jan 4 '14 at 1:23
• So this will convert back to TTL from RS-232 right? Now can this be made programatically in the Arduino, or is it impossible? Thank you. – Majid Laissi Jan 4 '14 at 1:27
• According to sparkfun.com/products/133 the MAX3232 is not necessary. Now that I don't need a conversion in my component (as it's already powred with +5V), this means the wiring will be simpler I guess – Majid Laissi Jan 4 '14 at 1:35
• @MajidL No, it can't be made programatically. The TTL levels are transformed to a larger bipolar swing by the MAX3232 chip, this can only be achieved with an external circuit. – alexan_e Jan 4 '14 at 1:38