Simple fault code reader.

[MBfreak]

My friend has a MB 420 1994. Great car. Has a fault code system you can read with a LED and count the number of flashes ( up to 32)

Would like to build a simple counter with 2 off 4 bit binary counters ( ie max count well over 32 ) that feed BCD to 7 segment ICs and then two 7 segment LED displays.

Being lazy I wonder if some electronics GURU on the GJ grouphas a ready made schematic.
I can probably make the schematic, but others no doubt do that better and faster

I am allergic to Arduino.

Ola

 

[AA/FC]

I'm not sure about vehicles that are built and sold overseas, but here in the USA, OBD2 became the standard in 1996 for all cars sold here. The "computers" in OBD2 vehicles do not put out "blinks" or "flashes". There is nothing to count. These vehicles put out "diagnostic trouble codes" via a scan tool.

 

[dave*99]

OBD-i is the predecessor to OBD-ii.
My 1983 Toyota blinked out trouble codes with check engine light (MIL). It was a 2 digit code. I think you had jump 2 pins together on a connector under the hood. The available codes were mostly tied to the emissions system.

 

[MBfreak]

Dear All
Thanks for the input. FWIW.
But rest assured that I know EXACTLY how the blink codes are pulled up and counted ( ie OBD1) in a MB W140 1994.
AA/FC, what is the info you try to get over wrt my post? OBD2 on a W140 1994??????
And ALL MB W140 were built in Germany, being sold "overseas " in the US.

Ola

 

[engineer2]

I'm no expert, but I seem to remember a round diagnostic connector on the fender well.
If so, adapters and readers may be available.

 

[MBfreak]

Enginner 2
You are right . There is a multipole diagnostic connector ( Black plastic) on the right fender wall.
Screwcap, diameter appr 50 mm.
All you need is a LED and a pushbutton to read the codes. But counting flashes is
a chore. Would like to get numbers.

Have made a drawing for a 6 bit counter using 74xx series ICs.
Counting up to 64.
Waiting to get the parts.
PCB a three island exp PCB 100x160 mm
Will post pic when ready and tested

Ola

 

[engineer2]

It should be an interesting project!

 

[iron block]

Ola -
Interesting project. A few comments:

1. Take care with the input signal conditioning. Your TTL counter will be eager to respond to any noise spikes on the input count signal. Since TTL is so fast, even sharp, short spikes could cause false triggers. And auto electrics are notorious for noisy signals...
2. Perhaps an RC low-pass filter into a Schmitt trigger inverter would be a good place to start for the input buffer. Oh, and clamping diodes to ground and +12 would be good.
3. Any chance you can find CD4000-series equivalents to your TTL parts? They will be much slower, which is good for this application.
4. Even though you are allergic to Arduino, this might be a good project to get your feet wet. The advantage to the Arduino ecosystem is that you can find drivers and accessories for all sorts of displays and controls. Want an LCD display that maps counted codes to text error messages? That is probably one afternoon's work with an Arduino. And if you want to add pulse-duty-cycle readout to your OBD1 tool (as needed for some of the fuel injection diagnostics, I believe) that would be simple to add. Something to think about?

Finally, one time I used a kid's pedometer (a.k.a. step counter) as the basis of a pulse counter. Just cracked it open and attached flying leads to the motion switch -- worked great for counting turns on a coil winding jig I built.

Good luck!

 

[AffableCurmudgeon]

Enginner 2
You are right . There is a multipole diagnostic connector ( Black plastic) on the right fender wall.
Screwcap, diameter appr 50 mm.
All you need is a LED and a pushbutton to read the codes. But counting flashes is
a chore. Would like to get numbers.

Have made a drawing for a 6 bit counter using 74xx series ICs.
Counting up to 64.
Waiting to get the parts.
PCB a three island exp PCB 100x160 mm
Will post pic when ready and tested

Ola

Too bad you are allergic to Arduino.
In my opinion, you can do it very easily and cheaply using an esp32 microprocessor board (basically Arduino), .96 OLED i2c display and a buck converter to convert 12v from the car to 3.3v for esp32 to accept as input signal.

Do everything software, esp32 will count the flashes and you can display it nicely on the OLED display.

Amazon.com

Amazon.com

 

[MBfreak]

Affable Curmudgeon.
I am sure your solution would be perfect.
However, my Arduino allergy makes it impossible. I may get Arduino rash all over me!
Made a drawing with a CD4018, a dual 4 bit BCDcounter and two BCD to 7 segment drivers.
2 large 7 segment LED displays in red.
I can then display 0 to 99, which is abt 3 times the number of blink-codes in a MB W140 4.2 liter V8
Ordered parts, will take a week.

Best regards

Ola

 

[MBfreak]

Code reader now breadborded.
Input circuit CD 4518 ( 2 off 4 bit counters in DIL 16 pin), 2 BCD to 7 segement CD 4511 and two 7 segment led displays
Seems to work well.
Input signal work remains. The CD 4518 is amazingly fast and will trigger on any "car type"transients.
This was also noted by poster ironblock above. Thanks.
Will put in analog SLOW and wide 0/1 conditioning . Small opamp slowed down in feedback circuit.
Or maybe the traditional antibounce circuit??

Ola

 

[iron block]

Congrats on getting the breadboard going.
If you can post a schematic, it might be possible to pass along a few suggestions for the input conditioning circuits.

 

[MBfreak]

Thanks Iron Block.
The CD4518 is a dual 4 bit BCD counter. Feeds two BCD to 7 segement chips CD 4511.
I connect pin 1, ie clockpulse to +-0 over a 1k8 resistor to have a defined input impedance.
The two resets , pins 7 and 15 are connected to +-0 when counting.
Switch over to +5 when reset.
Any suggestion on an input filter much wellcome.
I use a 1 Hz square wave 0/+5V on the clock pulse input, which works great.
But as highlighted above, the flashing channel in The MB M119 ( 5 lit V8) pulse is probably VERY full
of various transients which will wreak havoc with the 1-18 pulses I need to count.

It is a 92 car, no OBD2 and fault codes are read over a flashing led.
Which is easy to count, but I am more for a numerical display.

The MB500 with M119 engine is about the last MB that looks like anything but a hippo on speed
of the sedan cars. The asian markets have totally destroyed the MB style. The cabriolets are still nice.
Enclose a pic of my MB 220 SEb Coupe B from 1961. Real beauty. And manifold mechanical injection .
25 years ahead of the competition.
Bad eysight made me stop driving and sold my much loved car 5 years ago.
My friend loves his 1992 W140 car. Recently spent a bunch of money replacing the 8 injectors that sprayed
like a 82 yo male urinates . Caused havoc with the HC on low rpms. Now perfect. After 172 k miles

Best regards

Ola

 

[theoldwizard1]

A Google start

 

[MBfreak]

I bragged about my MB 220 SEb Coupe B in my above post. Alzheimer light. forgot pic
Here goes
Sorry yáll
Ola

 

[MBfreak]

The Old Wizard. Thanks. The UT is a bit out of date wrt design. But a good tutorial.
There is a much easier way with low component count.
CD4518 , a 16 pin DIL with two 4 bit counters. Count up to 256 binary or 99 decimal.

Ola

 

[iron block]

Ola, here is a rough draft of a front end for your CD4518 counter. Some notes:

1. From info on the web, it looks like the signal out of the diagnostic connector is normally high, and pulses low for data.
2. I assume that you are running the CD4518 at 5 volts, since you mentioned testing it with a 5 volt square wave. Therefore, the input pulses need to be scaled down from 12 volts to 5 volts, as well as having some noise filtering.
3. The diagnostic pulses are triggered by pulling down on the signal line for 3-5 seconds. This is done with a pushbutton.
4. The counters should be reset when the pushbutton is pressed. This will prevent a false starting count.

The attached schematic shows one way to tackle these points. The key ingredient is the 74HC14 Schmitt trigger. Its high input impedance is a good match for the RC input filter network. I would not suggest using a standard TTL part in its place.

 

[MBfreak]

Iron Block.
Thanks a LOT for your schematic.
About my only addition will be an optocoupler ( 4 N 35) that isolates the "counter" that runs on 4 AA cells from the transient rich car signal. I scoped that and I am pretty sure that the ignition pulses ( which are abt 18 kV before the plug fires) somehow slither thru onto the cable bundle on the right side of the engine.

Will build your excellent design and start field tests.

Best regards and kudos

Ola

 

[iron block]

After sleeping on it, I am not happy with the "reset circuit" in the original schematic. Attached is a revised schematic that should work better. It swaps a transistor in place of a diode, and uses one more section of the 74HC14.

The new reset circuit is not sensitive to the pulse timing coming out of the OBD system. The original circuit would not work as expected when fed slow, widely-spaced pulses -- which is, of course, exactly what would actually be present.

 

[MBfreak]

Thanks a lot.
The counter will be running on floating 5V to 6 V supplied by AA battery pack.
The pulse train in the car will be connected to counter over an optocoupler ( 4N35) thru your design of the schmitt trigger
In this way I hope to avoid disturbances from the car. Maybe I am overly careful, since engine is normally not running when code counting.
The reset will be a spring return switch that keeps 7/15 to zero ( ie NC) on battery pack and switch over to + 5 V battery pack
in NO spring position. Which has to be held in "NO"
The other pole in the switch will then connect signal wire in car to car 12 V Earth.
As long as the switch is in "spring" position the counter is zeroed and counting pulses are blocked.
After 3-5 seconds switch is released and fault code pulses are sent from car diagnostic ( Is this OBD 1 ???) and counted.



Best regards

Ola

 

[AffableCurmudgeon]

To be clear, is this what you are making, with digital counter instead of an LED that is on the device in this video?

 

[MBfreak]

Affable Curmudgeon
The one on Ricks movie is a late 80s model, very different socket .
Same idea but the car I am involved in is a 1992. ( W140 with a M119 5 liter V8)
It has a round device with lots of sockets placed in circular patterns.
Downloading code thru three wires , a push button switch and a LED is the same.
Would not be surprised if the " OBD 1" electronics are identical.
But not for engine/driveline.

Ola

 

[AffableCurmudgeon]

After sleeping on it, I am not happy with the "reset circuit" in the original schematic. Attached is a revised schematic that should work better. It swaps a transistor in place of a diode, and uses one more section of the 74HC14.

The new reset circuit is not sensitive to the pulse timing coming out of the OBD system. The original circuit would not work as expected when fed slow, widely-spaced pulses -- which is, of course, exactly what would actually be present.

Looks great. just a thought, if instead of the voltage divider for the incoming pulse, if you used a 12v relay to trigger a 5V signal into the counter circuit, would that not filter out noise and you won't need to worry about potential spikes.

 

[AffableCurmudgeon]

Affable Curmudgeon
The one on Ricks movie is a late 80s model, very different socket .
Same idea but the car I am involved in is a 1992. ( W140 with a M119 5 liter V8)
It has a round device with lots of sockets placed in circular patterns.
Downloading code thru three wires , a push button switch and a LED is the same.
Would not be surprised if the " OBD 1" electronics are identical.
But not for engine/driveline.

Ola

understood.

 

[MBfreak]

The CD4518 is fast and would maybe count several pulses on a normal small relay.
A mercury wetted reed relay would be better.
But do not have one and they are off limits now. In the sixties they were everywhere in industrial electronics.

But since I have time on my hands and need things to do so as to not worry about other calamities which are totally out of my control
I took the "full electronic " option.
For better or worse?

Ola