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Old 07-03-2011, 01:32 AM   #1 (permalink)
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clarification on OBDuino with PWM

To start I'd like to say that this opengauge idea is incredible. I always new you could get data off the obd connector (seen it with code readers, laptop readouts in mags, etc) but saw the only well known solution as scangauge. This tool does look nice but it's pretty expensive and no backlight at least from the looks of it. The DIY version should prove more interesting and lower priced.

Vehicle: Ford mustang 1998 coupe
OBD protocol: pretty sure it is J1850 PWM
(existing pins are 2, 4, 5, 7, 10, 13, 16)
Target: working OBDuino setup for data readouts

I've been reading through the documentation but couldn't really find any concrete pinouts for a PWM protocol setup. So far I have this

-freeduino with connections to buttons and transistor
-Interface: ELM320 instead of ELM327 (some searching on forums lead to some posts from advanced members providing this info )

Basically I need confirmation on two things.
-Do I use the ISO pinout or CAN pinout for the LCD connections?
-Is it ok to drive transistor from 5v on freeduino (read in a post that it was low current?) or should I tap into 7805 off of ELM320 OBD interface (pg 16 in datasheet)

EDIT: sorry I wasn't able to add links to info found/used.


Last edited by rs3275; 07-03-2011 at 01:34 AM.. Reason: No pic apology
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Old 07-03-2011, 03:13 AM   #2 (permalink)
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LCD connections are not related to ISO or CAN protocol - I assume you mean the OBD connections and not LCD?

Taking current from the 7805 (or adding your own) should be better, the pins I've seen are rated to 40mA (the digital pins, I'm not sure if it applies to the 5V, probably wouldn't harm anything).
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Old 07-03-2011, 10:21 AM   #3 (permalink)
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What I meant to say was do I use the LCD connections on the "ISO Diagram" or the "Schematic of the CAN Interface for the OBDuino Project by Frederic aka (Magister)". Both pics have an arduino, LCD, interface, and a lot of colored lines. ISO Diagram is in the guide portion and the CAN interface diagram is in the comments section ("error in a link must be" by x893...@gmail.com). It is just that both pics have some common pins but not all...

Closer analysis looks like this to me:
ISO Diagram
#########################
LCD------------->Arduino (digital)
pin1--------------ground
pin2--------------+5v
pin3--------------pin6
pin4--------------pin4
pin5--------------ground
pin6--------------pin5
pin7--------------N/A
pin8--------------N/A
pin9--------------N/A
pin10-------------N/A
pin11-------------pin7
pin12-------------pin8
pin13-------------pin12
pin14-------------pin13
pin15-------------transistor output
pin16-------------ground

Schematic of CAN Interface
#########################
LCD------------->Arduino (digital)
pin1--------------ground
pin2--------------+5v
pin3--------------pin3
pin4--------------pin8
pin5--------------ground
pin6--------------pin0 (analog in)
pin7--------------N/A
pin8--------------N/A
pin9--------------N/A
pin10-------------N/A
pin11-------------pin4
pin12-------------pin5
pin13-------------pin6
pin14-------------pin7
pin15-------------transistor output
pin16-------------ground

It is on the this page:

hxxp://code.google.com/p/opengauge/wiki/OBDuinoDiagram

Additionally I tried searching forums again for connections and found on thread which pointed to

hxxp://arduino.cc/en/Tutorial/LiquidCrystal

but it was actually different too...

I'm sorry if this might be fairly obvious, it's just that I've never interfaced to an LCD before. Would like to confirm which connections I should be using before going out to buy the parts.

EDIT: Ok, looks like it will let me post links with the hxxp start, just need to use that till I can post links.

Last edited by rs3275; 07-03-2011 at 10:26 AM.. Reason: note for references
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Old 07-03-2011, 07:56 PM   #4 (permalink)
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The display pins themselves won't matter compared to the pins used for the car communication circuit.

Have you seen: OBDuinoInterface - opengauge - OBDuino OBD2 cable and Interfaces - Open Source Fuel Efficiency Instrumentation - Google Project Hosting ?

That shows the circuit for ELM327.

The LCD pins should be able to use any of the digital pins not consumed by the car communication circuit.

Figuring out the pins for the LCD to match with the code should be easy enough with the datasheet, but I happen to remember them:

16 - Backlight Ground.
15 - Backlight Power
14 - DB7
13 - DB6
12 - DB5
11 - DB4
6 - Enable
5 - Ground
4 - RSPin
3- Contrast.
2 - 5V
1- Ground

// LCD Pins same as mpguino
#define DIPin 4 // register select RS
#define DB4Pin 7
#define DB5Pin 8
#define DB6Pin 12
#define DB7Pin 13
#define ContrastPin 6
#define EnablePin 5
#define BrightnessPin 9
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Old 07-03-2011, 08:12 PM   #5 (permalink)
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That is really reassuring, thanks for confirming that info. I think I am just about ready to get all the parts ordered. I did read through the ELM327 chip diagram circuit and like its all-in-one ability. Didn't really like the price though... ~$40 shipped.

I think I'm going with the ELM320 as it is all I need. I was looking at the connection between the obd port and the special "interface". Do you recommend an OBD2 to DB9F cable or is a OBD2 plug with only needed wires ok? was worried about interference and gauge.

Also do you recommend hooking the arduino to +12v/signal ground (on all the time) or switched +12v/signal ground (like cd player)?

Happy 4th of july!


Last edited by rs3275; 07-04-2011 at 06:06 PM..
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