What speed is the serial port capable of.. I've been trying to find something that had multiple serial interfaces that can do 56kbps or less, but this one also looks interesting for another project I'm working on.

 

You mean that dontronics stuff?
They use an Atmega128 (64Pin) witch has 2 UARTS at 16 MHz.
The baud rate can be selected with the prescalers. So you can't use every theoretic value.
You can find this informations in the atmel datasheet (quite big).
http://www.atmel.com/dyn/products/pr...p?part_id=2018

 

244 baud is the minimum I calculate from a 16MHz clock. Maxmimum speeds are silly, 1M baud I think.

 

so this would allow me to log without a laptop, sweet! and the paramaeters i need that a pocketlogger doesn't do, like octane number and load. so will you be making these available to those of us that can't follow a schematic or build it? PM me some of the info for getting my hands on one of these. any plans to make it work through the tactrix cable?

 

Would this work to interface the Butterfly to the OBD plug?

The NPNs with pull up resistors to 12V will invert the signals (the Butterfly has inverters on its UART in/outputs and you can't get to the in/output pins from the uC, but I don't think it does full RS232 level conversion).

I don't think the Butterfly can output a negative voltage when I look at its schematic. http://www.atmel.com/dyn/resources/p...ts/doc4271.pdf page 36

 

When your dealing with RS232, TTL voltages are different. On an average RS232 port the voltages your dealing with are very low.

You should be isolating the signals, feeding 12v to the RS232 would damage the IC.. But your right, in order to do a full RS232 conversion, the voltage must be lowered or isolated from the RS232. Handshake and flow control signals are not used at all. On a car with an L and K line, or in a cable capable of reflashing, the additional terminal (RTS/CTS, DCE/DTR) lines would be used to activate the reflash mode, or swap the lines.

You can use 12v as a power supply, and the ground, but that would be fed to a regulator for the electronics.

Most OBD-II PC cables use some sort of opto-isolation to protect the port.

 

Thanks Jack. I've tried to account for the factors you mention in the circuit I showed which should invert and level shift appropriately, but I didn't include opto-isolators as the Butterfly inputs are diode shunted and inverted as per the schematic (so they are designed to take +-12V RS232 voltages) and the device is cheap if I do fry it. I expect the ECU will also have input protection, but the Butterfly has a 3V battery and no charge pump to produce negative voltages, so I can't see it doing any damage to the ECU. I wanted a minimal count modification of JoeBee's circuit to work with a Butterfly. The Butterfly works off its own battery.

So with all this in mind, anyone any comments on the circuit I posted as a modification to JoeBee's to work with a ready built micrcontroller board which has a low voltage RS232 converter on the Tx and Rx lines?

 

I'm wondering if VAG COM - RS232 cables would work:

http://ucables.com/ref/OBD2-KKL

Although it does the 2nd K-line and the L-line, it is supposed to be ISO 9141-2 compatible.

So if I just have the microcontroller board with MAX232 or similar RS232 interface it should just plug into its serial port?

 

Yes, the vag com cable will work. the USB FTDI Chipped version of the cable works with mitsulogger.. the extra K and L lines are basically not used on the EVO so its just a little bit of extra electronics.

Just keep in mind I think several of the OBD-II port pins are wired for other functionality (its not documented in the wiring diagrams) which could trigger some other functionality, but I have not experienced this on my car or my bench ECU as its not ECU related as there are only 2 connections to the ECU from there, but possibly the ACD which isn't present in my car.

 

Thanks, I think I'll try one. I need to find a board with a compatible processor and ideally display as JoeBee's one to use his software.

The ideal would be to be able to get off the shelf assembled parts and cables to open this project to a wider audience.

 

http://www.one-stop-factory.com/big....2063scheme.gif

This schematic is for a KL RS232 cable.

I think it will do the trick - usually microcontrollers wouldn't have pin 7 on the RS232 wired anyway so the L line will just be pulled up to 12V.

 

In reality if you were to use the serial port the way I do on the microcontroller I have, I'm only using RX/TX an GND on the port I created. so any of the additional pins wouldn't have been connected regardless. Most microcontrollers allow serial communications on their regular digital I/O lines through a special mode, many already have pins dedicated to that, so you don't have to use the RS232 port that is used for the terminal or Programming. The advantage of using the I/O lines is it allows unusual baud rates that the dedicated RS232 port might not allow.

 

Never done an LCD hook up to a microcontroller before.

Here it is after a bit of soldering

Note the RS232 port on the top which should connect to my OBD cable that is coming.

I'm proud of it anyway

 

Nice hardware.. hehe.. I really like that you guys are taking the initiative to build portable devices, even I had something coming together for some time before my free time started becoming limited.

 

The potential for this stuff is just awsome. I can't wait untill we are able to have pocket logger devices that log to some kind of flash memory or a pocket flasher that allows you to switch between maps.

Nice work to everyone contributing to these projects.