Any electron wranglers able to think out a simple circuit ?

[Reman]

Hi all. I've been trying to work something out, but it seems I'm a moron when it comes to anything more complex than replacing burnt out pre existing components on circuit boards.
I'm trying to work out a simple 12v circuit that I can cut into my car's wiring that will automatically simulate a button press just after I turn on the ignition. The circuit just needs to wait a few seconds before powering a transistor for a second or so, then shutting it back off again, but it's been so many years since I had to think out a circuit from scratch that I can't even think out something this basic now.

I'm thinking what I'm looking for would be a kind of bistable flip flop circuit, But I can't work out how I'd stop it after just just the one On/Off flip. It's also possible that there's now some cheap all in one chip out there that I don't know about.

Anyone here good enough at all this electrickery to point me in the right direction?

 

[Dave-sparks]

Off the top of my head you'd need something along the lines of a 'one-shot timer' circuit

 

[Johnnybravo]

What, like something to make it look like the abs light works?

 

[gaz1]

just use a relay and push button

 

[blackolive (Ste)]

Someone already has

LED Car SRS airbag light timer switch time relay 1-10 sec kit delay off 12V 0.15 | eBay UK

The kit is designed to repair always on airbag light for LED airbag lights up to 2.5W. Step 2: Ground theblack wire. Width: 28 mm. This approach will expedite the resolution process. We are committed to assisting you throughout the entire process.

www.ebay.co.uk

 

[Reman]

I didn't really want to say, As I'm pretty sure it comes under "tampering with emissions system", But it's that bleedin' stop start system. For the kind of short trips I do it just runs the battery flat without the trip being long to recharge the battery. I usually turn it off, but thats only after it's activated once per trip. I just want it to automatically be off, and I can re enable it if I'm doing a long trip around a town.

I could just disconnect the sensor on the battery positive terminal, as the system disables if it can't tell the charge state of the battery, But that would also prevent the system from being turned on.

 

[gaz1]

I didn't really want to say, As I'm pretty sure it comes under "tampering with emissions system", But it's that bleedin' stop start system. For the kind of short trips I do it just runs the battery flat without the trip being long to recharge the battery. I usually turn it off, but thats only after it's activated once per trip. I just want it to automatically be off, and I can re enable it if I'm doing a long trip around a town.

I know what you mean

but you will invalidate your car tax bracket with the adaption as well

 

[Reman]

Now you see why I didn't want to go into too much detail about this purely theoretical idea.

Though to be honest, I think VW already "Invalidated its tax bracket" by lying about its emissions in the first place.

 

[voipio]

Something like:

https://cpc.farnell.com/bentley-security-projects/at-449/timer-everytime/dp/HK01119?st=time%20delay%20relay

Looks like it should do the job, but the datasheet is a bit thin on detail.

 

[GRW]

You could do something like a simple countdown timer and relay?
Ignition on triggers the timer.
When timer elapses and makes the circuit, which closes the relay coil and switches the relay, which mimics the button press.
Then, wire a parallel circuit with a manual switch in series in it, so when the manus switch is made it restores the normal function of the system.

(I know that's a bit rough n ready, but it was straight off the top of my empty head )

 

[hotponyshoes]

What car is it?
Is there not some other form of workaround?

 

[bricol]

But your extra circuit will surely prevent it being switch on too?

If disconnecting the sensor to the battery will switch it off, why not simply extend the wires into the cabin, and add an on/off switch out of the way? Then when you remember and want it on, just flick the switch back to on.

If you can find the right plug/socket, you could simply insert it in-between the sensor and battery so you can easily remove it for service or sale.

 

[tom2207]

In many cars you can turn off the stop start if you have the diagnostic tool that lets you do coding , the cheap universals wont do it though.

 

[500e]

Cheaper to look at some ready made boards in CPC

 

[Reman]

What car is it?
Is there not some other form of workaround?

It's a mk6 golf TDi. There is a workaround that disables it by tweaking the code in the ECU, but apparently this fiddling completely disables it, and that would be an MOT fail.

But your extra circuit will surely prevent it being switch on too?

No, the idea is to just have the circuit short the switch wires to simulate a button press. The original switch would still be connected as it was before.

If disconnecting the sensor to the battery will switch it off, why not simply extend the wires into the cabin, and add an on/off switch out of the way? Then when you remember and want it on, just flick the switch back to on.

As far as I can tell (The Haynes manual wiring diagrams for this model of golf is half way between inaccurate, and totally fabricated guesswork !) the sensor's takes 12v + directly from the positive battery clamp that it's built onto, and is earthed through the cars 2 CANbus wires. It does some jiggery pokery to also use those 2 wires for data. I've seen enough random issues when people have been messing with CANbus wiring to not really want to play with connecting extra wire into it if possible. Disconnecting the sensor also throws up a fault message that I don't want to mess with every time I start the car.

The idea I'm playing with is just a simple circuit that will automatically simulate a button press to turn the system off whenever I start the car. Where the button goes is right next to the ciggy lighter socket, and on these golfs they power up with the ignition, so powering the board shouldn't be a problem. All it needs to do is wait a couple seconds after powering up before it pulses a transistor to short the switch wires and simulate a button press. I'm sure there must be a way of doing it where the 12v in charges a capacitor until it let's through enough juice to wake up a transistor to simulate the button press, but the tricky bit is to then kill the power to the capacitor so it can drain down and have the transistor stop bridging the switch wires (And only have it pulse the transistor once rather than flip flopping on and off all the time it has power).

 

[500e]

HK00721 timer board from CPC
May suit about a fiver

 

[MysterG]

In our Fiesta the stop start monitors the battery level and will not work if its too low even when turned on. Surprised all cars would not do the same.

 

[sako243]

How about introducing a 555 into the circuit?

Something along the lines of:

Generating a delayed pulse of 0,5sec with one 555 timer upon powering up the circuit

In the link below, this circuit I found is what I needed. Only the length of the pulse and the delay are not what I want. When I want just 0.5sec before pin 3 is up and the pulse duration I want i...

electronics.stackexchange.com

 

[Reman]

HK00721 timer board from CPC
May suit about a fiver

Oddly enough, I was just looking at that. The problem is, I'd need to work out how to make it stop after one On/Off cycle.

In our Fiesta the stop start monitors the battery level and will not work if its too low even when turned on. Surprised all cars would not do the same.

Yeah, the golf does that too. That's the sensor I mentioned about disconnecting a few posts up above. The tweak to the ECU code I mentioned actually changes the parameters for the stop start to be active. It raises the minimum acceptable voltage up to a point above what the battery can put out. Trouble is that this means it's totally disabled unless you get the ECU RE reprogrammed again, and as far as I know, it seen as emissions control tampering, and is subsequently an MOT failure.

How about introducing a 555 into the circuit?

Yeah, a 555 chip based circuit looks like a pretty good candidate. I built a little board with one several years ago to automatically fold the door mirrors in on my old Lexus IS200 when I remotely locked it. It was a very handy "OCD calming" visual confirmation that I'd actually locked the car when looking back at it from the other side of the carpark.
Thinking of that, I'm just going to see if I've still got the circuit diagram I used for that. It might be a usefull starting point to work this out from.

 

[500e]

@Reman did you go through all of them I am sure we used a one shot timer on a job.
Some have 4/5 modes jumper driven
I try never to reinvent the weel