Hi Everyone,

My car has a couple of annoying functions enabled by default that manually need to be disabled each time you start the vehicle by pressing the steering wheel buttons. Yes, I know it should be no big deal but it annoys me, so please forgive me.

I've looked at the vehicles circuit and each button just places a resistor to ground to change the voltage in a voltage divider circuit.

Hence to simulate pressing the two buttons, one after the other, I need a circuit that will connect a resistor (R1) to ground for 5 seconds after the car is started and then disconnect. It should also connect another resistor (R2) to ground 15 seconds after the car is started for 5 seconds and then disconnect.

This would simulate the pressing of the two steering wheel buttons.

Thoughts?

 

Do you have a signal the indicates when the car is started?
The rest is relatively simple.

 

Do you have a signal the indicates when the car is started?
The rest is relatively simple.

The only thing I have is Power (12V). So the timing must start when power is applied to the circuit. Power will remain until the car is turned OFF.

 

he only thing I have is Power (12V). So the timing must start when power is applied to the circuit.

Is that the accessory 12V that only appears after the car is started.

 

Is that the accessory 12V that only appears after the car is started.

No, the car has two ON positions Accessory and Started (or ON). In the fuse box there's Acc. Power and ON Power. I want to use the ON Power to start the timer. No point using the circuit when the car is not started/running. Hope this makes sense.

 

I want to use the ON Power to start the timer. No point using the circuit when the car is not started/running. Hope this makes sense.

Does not to me.
The ON power is there when the ignition is turned on to start the engine.
You want the Acc. power which is not on when the starter is engaged, so then when it appears, ostensibly the engine has started.
That's when you start the timer.

I would think there's no problem if the timer is engaged by the Acc. power for listening to the radio, etc. when the engine is not running.

 

I need a circuit.

Analog or microprocessor?

 

Analog or microprocessor?

Analog please.

 

The ON power is there when the ignition is turned on to start the engine.

Correct and stays ON when the engine is runnings. I can't drive the car until the engine is running which is when the timer will start.

 

I can't drive the car until the engine is running which is when the timer will start.

How so?
The timer will start when the ignition is turned on, before the engine starts.
That's why I suggested using the Acc. power, which is off during engine start, and goes on when the starter goes off.

 

That's why I suggested using the Acc. power, which is off during engine start, and goes on when the starter goes off.

Understand now, you are correct. Sorry.

 

Analog please.

 

Here's the LTspice sim of a simple circuit to do what you want:
This circuit will have some variation in timing due to its simplicity, but I assume your time values are not critical.
You could use 555 timers instead as sghioto showed, to get better accuracy if needed.

As you can see, R1 is connected to ground for the first 5 seconds (yellow trace) after the Acc voltage goes high (green trace) and then R2 (red trace) is connected to ground for 5 seconds, 15 seconds after that.
(Note that the top of R1 and R2 are connected to the Acc voltage for the simulation, but are actually connected to your voltage divider circuit.)

You can tweak the values of R4, R5, and R6 to adjust the times if necessary.

 

Hi greg,
Have you contacted the manufacturers of the vehicle to ask why these buttons are configured as to require the driver to operate them before driving?
Are they safety interlocks of some kind?
E

 

View attachment 327838

Looks great thank you. Any reason for the FET etc in the 15 sec timer?

 

Here's the LTspice sim of a simple circuit to do what you want:
This circuit will have some variation in timing due to its simplicity, but I assume your time values are not critical.
You could use 555 timers instead as sghioto showed, to get better accuracy if needed.

As you can see, R1 is connected to ground for the first 5 seconds (yellow trace) after the Acc voltage goes high (green trace) and then R2 (red trace) is connected to ground for 5 seconds, 15 seconds after that.
(Note that the top of R1 and R2 are connected to the Acc voltage for the simulation, but are actually connected to your voltage divider circuit.)

You can tweak the values of R4, R5, and R6 to adjust the times if necessary.

View attachment 327837

Thank you very much for all your time, this will help greatly.

 

Looks great thank you. Any reason for the FET etc in the 15 sec timer?

That's the 5 sec timer that pulls R2 to ground after the 15 second delay.
It can be done with a 3rd 555 more precisely if needed.
I say that because as the timer times out after 5 seconds the total resistance which is R2 plus Q1 will begin to increase and not sure if that would be a problem.

 

That's the 5 sec timer that pulls R2 to ground after the 15 second delay.
It can be done with a 3rd 555 more precisely if needed.
I say that because as the timer times out after 5 seconds the total resistance which is R2 plus Q1 will begin to increase and not sure if that would be a problem.

Understand now, thank you again.

 

Here's a full 555 version:
View attachment 327874

Thanks once again. Any reason not to use 556 for the 15 secs timer?

 

Thanks once again. Any reason not to use 556 for the 15 secs timer?

No reason not to.