Need help with simple (I hope) auto circuit

Status
Not open for further replies.
Last edited:
This Android app is really cool. Torque. https://torque-bhp.com/wiki/Main_Page It requires a OBD to Blutooth adapter to run.

Basically, I don't know if you can add a PID. I think the OBDII info is available to buy from the SAE.

https://elmelectronics.com/obdic.html Again, I can't help much.

I have the torque app and it's really cool. I also have a scanner. I had an issue with a vehicle where the BCM had to be programmed and that HAD to be done with a Tech2 scanner. I did have an opportunity to talk to the guy which had his own company specializing in OBDII diagnostics and programming.

Newer vehicles will use the CAN bus.
 
Last edited:
I have the torque app and the blutooth adapter as well. I have added the diagnostic port to my J10 project and like playing with the app, been handy with this project. I used this site LT1swap for all of my harness mod info and he reprograms the PCMs for $75, great source of info.
 
Ok so you need your switch to latch a relay to turn on a light if the switch is pushed and unlatch if the switch is hit again or power is reset.
This should not be to hard.
 
This should in theory do the trick, but there's no absolute guarantee it will stay in sync with the transmission mode shifts. I've modelled the effects of 50V voltage spikes on the nominally 12V supply taken from the ignition switch. R1/ZD1 suppress these. When the ignition is switched on, C4/R3 provide a lengthy reset pulse to U1b so that the LED is initially off. Button presses are assumed to provide a 5-0V clock input to U1a which is configured as a monostable to suppress switch bounce.
 
 
Thanks Alec, I think with your help and the other links that KISS found I can round up some parts and do a little testing. It looks like there are a couple ways to skin this cat and it is something that can be done.
4pyros, I would like more info on your thoughts if you get the time too.
Thank you guys.
 
Last edited:
I reached out to someone I know and got the following response:

Chevy truck: I would have to ask if he had it programmed using gm's tis2web site and had the Vin# written into the pcm. Gm uses the same controller for many applications and during programming that tells the pcm how many cylinders the engine is, if it has an egr valve or not, etc etc. As far as sniffing the data bus, that's possible but it depends on what system it has. If it's 05 and up then it's CAN. The way the system works is there is a button on the shifter that when pressed, grounds a terminal at the pcm which tells it to go into tow / haul mode. Once it's in that mode something tells the cluster to turn on that indicator. That something could either be a CAN bus message from the pcm or a hard wire if it's not CAN. If you get me more info, year, make, model, and engine size I can look it up. Since it worked before the new pcm I'd have to wonder if it's the correct pcm and or wasn't programmed correctly.

OK, so we know there's a slight miscommunication here. You have the wrong dash with no light probably.
 

Hmm, yes miscommunication maybe. I have not swapped the original dash into the jeep from the 2002 GMC yukon. The components swapped were the engine, engine harness, transmission and and PCM. I had the PCM reprogrammed by a fellow from lt1swap.com who does many for people and is very good at it. Yes, I did have to specify the VIN and other options as well as tell him of other functions I wanted enabled/disabled. I did specify that I wanted to keep the tow/haul function. The swap is pretty much complete and I have driven the truck. I can tell the difference in shifts when the button is pushed so I know the function works. After all simply pushing the switch and grounding pin 71 is all that takes to enable or disable the function. The original indicator was turned on with what they called "class 2 communications " through the BCM which was tied into the original dash as understand it and as I have stated, I didn't use the BCM in my build.

Everything works like it should right now when I push the button, but I don't get the nice visual. This is why I asked for a circuit that simply turns on a light or LED whenever a momentary switch is grounded. It really has nothing to do with anything but that simple request.
I hope that helps clear it up a bit.
Maybe I should have just asked for a circuit that turns on a lamp or LED whenever a button is pushed and leaves it on until the button is pushed again and left out all the other stuff. lol
 
Last edited:
Hey. I like looking at alternate solutions and there is no harm in doing so. My MOA is generally always look at all options,no matter how absurd and then star taking them apart.
A lot can be learned in doing so.

So, you probably don't have class II data to even look at and the BCM probably controls the dash.

So, maybe abandoning the "snooping" is a good idea.

I have an idea that's pretty easy and probably about $5 and uses one part. OK, a few parts. Make your switch DPST rather than a simple SPST (NO). Use the second circuit to operate one coil of a magnetic latching relay. So, when you push the button, the state stays forever, with and without power.

Then find a signal, like +12 when the car starter is turning and use that for the reset coil. So, a car start will cause tow/haul to go away.

You'll need diodes across the relay coils.

I picked an example part: https://www.digikey.com/product-detail/en/TQ2-L2-12V/255-1008-5-ND

A dual-coil magnetic latching relay basically consists of a manet and a coil to "push" the contact. The transfer and hold magnetic fields are different, so removal of power keeps it in the stuck state, Both single and dual coils have polarity markings. They really don;t have to be followed, but a reverse polarity applied to the set winding would reset the relay. That's how a single coil relay works. One polarity sets and another resets.

The starter turning would be a nice signal that's +12 when starting and it goes away later.

Otherwise, there's a lot more involved with signal conditioning, power on reset, power protection and even isolation. A lot of electronic devices are uncomfortable having a signal applied to them when the power is off.

Make sense?

EDIT: This won;t work quite right, because all pushes turn it on and all starts turn it off. You need the pushes to toggle.

EDIT2: The ELM411 https://www.elmelectronics.com/ebench.html#Switches could do it. It can't drive a LAMP directly. It does need a 5V supply and it would be better to use a set of isolated switch contacts. The power choice would be from the ON side of the ignition.

A simple n-channel logic FET can be used for a LAMP/LED driver or a ULN2003/ULN2004 could be used depending if you wanted to drive the LED from the 12V or the 5V supply.
 
Last edited:
If you already have the switch mounted, I think an LT6703HV-2 or -3 with the proper glue logic would work to allow a single SPST switch to work. My brain is too fried to come up with a circuit and to figure out which one is needed. Of course it needs a few extra parts.

You will note that the -3 and -2 determine which way the comparator works. >400 mV or < 400 mV (I won;t say respectively). It would need bypass caps and an inout protection and possibly a pull up resistor.

In any event, I'm assuming that the circuit is normally at +5 and you take it to below 400 mV with a switch.

The next thing you need to determine is what you want the lamp supply to be (+5 or +12) and what the lamp is going to be. A simple LED? One other thing is if there is a dim circuit available that you can power the LED with, probably with these new cars, the answer is going to be a no.

Some lamps on a 2000 non-chevy vehicle of mine are always on a full brightness. i.e. traction.

If you uncomfortable dealing with SMT stuff. www.proto-advantage.com will buy and mount digikey parts on a DIP header and ship to you.

What do you think, Alec?

The standard reverse polarity and transorb (TVS diode) protections would apply too,

If you wanted to get fancy, you could use something like the parking lights on to set a different level of brightness for the LED.
 
I found this switch on EBAY, **broken link removed** It's a momentary switch with a built in LED. Do you guys see this as usable component that might merge what I'm after and what you're coming up with?
Thanks
 

Attachments

  • $_57.JPG
    284.3 KB · Views: 336
Last edited:
• QTY: 1PC
• 100% New and high quality
• Head diameter 18mm
• Button diameter 10mm
• Hole size required 16mm
• Depth inc contacts 35mm
• Metal button [Flat Head]
• Switch rating: 3A/250VAC
• Led voltage: 5-12VDC
• Contact Configuration: 1NO 1NC
Warning:
The normal operating current for the LED light is 20mA.
Please aovid using the excessive current to cause it too heat then it will reduce its service life.
 
Alec:

The idea in general. The comparator comes two flavors (greater than, Less than). It's mostly Overvoltage protected. With a resistor in series with it's input (say 10K) it's protected.

I'm ASSUMMING, that the line that needs to be grounded is pulled up to +5, but even if it is't, it should still work.

The ELM411 takes care of the toggling and does a power on reset and has a pull-up on input 3 A FET or a ULN2003 can do the driving of the LED. You can get the ELM in SMT or DIP.

All of the stuff operates on 5V, but takes a tiny amount of power, so one of those small linear 5V regulators could work.

You still need to decouple and add some" automotive protections" The problem is figuring out what flavor of the comparator to use, otherwise the light will be ON an power up.

12 V supply with protection (200 PRV diode, 18 V TVS)
5 V supply with bypass caps and filter
Input Protection (10K)
Comparitor with bypass caps
ELM411 with bypass caps
Driver - simplest is a logic N-FET to +12 or (the UN2003 part).

Misc. PCB, case, connectors etc.

EDIT: The 5V supply has to collapse rapidly to preserve reset.
 
Last edited:
The illuminated switch in post #38 looks suitable, as does the ELM411 (provided switch bounce is less than 25mS). How do you envisage the comparator being used, KISS?
BTW, as I read the ELM411 datasheet it is the power-up time, not collapse, which is critical to the reset?
 
Status
Not open for further replies.

Similar threads

W
  • Question
GM LS D585 Coil Pack Oscilloscope Trace Running without ECM - What am I looking at? Auto Fire ?
Replies
8
Views
3K
waid786
W
R
  • Question
auto electrician courses recommendation please
Replies
6
Views
4K
Tony Stewart
S
  • Question
Need help identifying this component
Replies
6
Views
8K
Diver300
D
K
B57825 Philips IC Help
Replies
2
Views
401
k-krzych
K
Z
  • Question
URGENT HELP!!! Can I add a second camera source using 2 in 1 RCA splitter cable?
Replies
2
Views
1K
Les Jones
L
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…