Auto Trouble Code Reader Circuit

[mikeu]

Hi,<p>I've got a 1987 Ford Ranger truck (OBD 1) that I need to read the engine trouble codes. The manual says that you can use an analog meter and count the meter deflections to obtain the numeric code.
Does anyone have a more elegant circuit solution or can point me to a website for building my own reader? I have a listing of the codes.<p>Thanks

[Chris Smith]

Leds that blink!<p>Thats how the system works, "X" blinks equal a code, and then you look up the code. <p>To reinvent this wheel would be down right silly.

[philba]

well, one thing that would be useful is a simple pulse counter so you wouldn't have to contrive to have the meter visible when you create the situation that causes the error code.<p>For a simple circuit, I'd use a counter and drive LEDs. The number of "deflections" would be viewed as a binary number on the LEDs. I'd use a 4000 series cmos chip since they can run at 12V or off of 2 1.5V batteries. The 4020 is a decent choice ($.60 Mouser). Other counters will work as well. Hook an LED to each output (with a dropping resistor) and the input of the chip goes to your probe/clip. If you use batteries, you will need to divide the 12V input down to what ever your battery voltage is. You might need to put a schmitt trigger on the input (40106 $.55 Mouser). Use enough LEDs to count all of the codes. (16 or less is 4 LEDs, for example).<p>I'd include a reset switch, though a power switch would do just as well. A diode on the input to prevent reverse voltage would be a good idea too. <p>Another thing to consider is a low pass filter on the input to filter out noise that might get counted. I'd try something like 100nF and 100K ohms to give you about 16 hz 3db cutoff frequency. (cap between input and gnd, r in series between cap and input). You might want an even lower cut off frequency. I'd look at the the timing between the deflections to figure out the frequency you'd want to let through. Here's a page to help you figure out the low pass values. http://www.st-andrews.ac.uk/~www_pa/Sco ... s/lpf.html<p>You could probably build this for a couple of bucks if your junk box has the right stuff in it.

[Chris Smith]

If it counted to a million, I would agree.
Four, nine, twelve blinks right under the dash, after you have to crawl under the dash to short out two pins....etc,....?<p>Well thats more parts than the original wheel? <p>And If your in the biz, you buy a device for at least $9.99, and If your not, you read these blinks at least every five years or so? <p>And then if you know what to do with the blinks, your a mechanic with bigger things to fry.

[philba]

I dunno but when I'm messing with a car, it ain't always easy to get to the meter. Having to watch what I'm doing and what the meter is doing is a bit too much for me. <p>I'll take your word on the original wheel - I'm sure you were there...

[Chris Smith]

The problem with counting the codes is how to count the pause and add up the flashes as well.

One, pause, Three, pause, One pause, ......Repeat over and over til you get it,.... is not that hard to read. That’s Cadillac for Knock sensor. Takes but a minute. <p>The other way will cost you more than a $1.99 in parts and time, a lot more.<p>Inserting a meter is nothing more than the proper terminals, inserted, and alligator clipped on. Sit back in the leather seat, crank up the AC and Radio and count. That and a tiny switch to launch the codes.

[yesiamwds]

How about a little PIC processor with an input counting pulses and then spitting out a trouble in real words on a little 16x2 LCD. May be a lot of work just to find out it's time to change the spark plugs.

[HighFrequency]

But it would be pimpin'! LOL<p>(Did I just use the word "pimpin" ?)

[mikeu]

Hello All,<p>Thanks to everyone that replied. I took the easy way out and used an led, limiting resistor and switch. I was able to get the codes - now I just have to fix the truck!<p>Mike

[peter-f]

- there you go!<p>[was easier than all that "official procedure" stuff, too!]

[Chris Smith]

Now onto the hard part Mikeu, fixing it!