RS-232 connection problem

Projects Networking, Protocols, and Devices
1

Hi!
My project:
I'm working on a project where an arduino is used to read values from the ECU of a car and present it on a LCD-screen. The ECU is sending the information continuously using RS-232. I'm using the MAX3232 chip to read the data.

My problem:
The connection seems to be completely dead. Not even the RX-led on the MAX3232 module blinks when connecting it to the ECU.

Current debugging:
I have recorded the data-stream from the ECU using a PC and a usb-to-serial adapter and sent the data to the MAX3232 using the same serial adapter and everything works as expected which at least means that the hardware and software are working, but not together...

Do you have any clue what might cause the problem? I'm new to RS232 so might be something stupid...

MAX3232 chip I'm using:

Serial to USB adapeter (something similar):

ECU:
http://www.vems.hu/

2

You connected the ECU, RS232 to USB adapter, to PC and data was transferred to the PC and you could see it looked correct.

You sent the PC captured data back to the RS232 to USB adapter, and then the MAX3232. you say that worked. But did you receive the data on the Arduino? Why did you not test this? How did you power the MAX3232? Did you use 5 volts or 3.2 volts?

Paul

3

Hi Paul!

Sorry for the bad explanation. I've streamed the data from the PC to the MAX3232 when it was connected to the Arduino project and everything shows up on the LCD as expected. So every single component is doing its thing perfectly in that setup.
When the ECU- and MAX3232 connectors are connected into each other it appears to be silent. I've tried both 5V and 3.3V for power and there is no difference.

4

ErikLusch:
Hi Paul!

Sorry for the bad explanation. I've streamed the data from the PC to the MAX3232 when it was connected to the Arduino project and everything shows up on the LCD as expected. So every single component is doing its thing perfectly in that setup.
When the ECU

Then the remaining possibility is the ECU is waiting to be told the proper RS232 connections have been made and it can begin sending data. The PC connection must have been setting a DTR or data terminal ready pin to some + value, greater than +3 volts.

Set you PC to ECU connection again and see what voltages relative to ground you read on the connector going to the ECU. You will have to match that voltage with your Arduino to ECU connection.

Also check the voltages on the pins of the ECU connector. You may get lucky and find a positive voltage on a pin you can use to jumper to the ECU pin needing the voltage.

I don't have a RS232 connection for a 9 pin connector in front of me, so I can't suggest a possible pin.

Paul