boot/trunk remote closure

[installer69]

Hi, my car has remote boot/trunk opening but you have to push a button on the lid to close it.

After much playing I have located the wire in the latch that goes +12v when the remote is pushed to release the latch and the wire in the close button that goes to earth when pushed to close the lid.

At first I thought that a simple 12v relay would do the trick but the (quite sensible) issue is that the close button is inactive whilst the latch is receiving the open pulse.

So, I made a little circuit with 2 555 timers, The problem is my circuit requires an earth trigger and provides a +12v output pulse after 1 second which works perfect but means the addition of a relay at each end. I have been pointed in the direction of a 4001 which may do the trick but cannot understand enough about one to allow me to do what I want so this is where I ask for your help.

Just to reiterate, The boot release button provides a +12v pulse and my circuit needs, after a 1 second delay, to send an earth pulse.

Current circuit attached but press switch to activate on left hand side of picture has been replaced by a +12v triggered relay.

Also, at the moment I have the circuit powered from the trunk light so that it is only powered up when the lid rises but the circuit goes through its cycle when first powered up and sends the close trigger before the lid is fully open thus stopping it half way up. I could change caps/resistors to extend the delay or power the circuit all the time but both options seem messy if there is a simpler one chip/no relay solution.

Many thanks

 

[jpanhalt]

Why do you have the first 555 (first = left side)?

EDIT: Never mind. I woke up and re-read your post. It is a delay.

John

 

[installer69]

OK, can someone help me to add a reset on power-up to the above circuit? I think this may solve my problem?

 

[jpanhalt]

There are a lot of power up reset circuits (search: 555 power up reset). I have found Paisley's site to be quite informative. Check out #10: **broken link removed**

John

 

[installer69]

Thanks John,
I had come across that but was unsure whether it needed to be on the first 555, the second one or both?
I think it may be easier if I convert to a single 556 then there will be no choice!

 

[installer69]

I changed the 47k resistor from 6/7 to +v to 150k to extend the delay time which worked but of course this leads to a longer delay before the lose action so I would rather find a solution to preventing the cycle upon power up. I tried the paisley option on the first 555 and it wouldn't fire at all.

 

[jpanhalt]

Sunday night dinner at home, so I won't have time tonight. I will look at it later or tomorrow.

John

 

[dougy83]

You can most likely get around the startup problem if you connect the 22uF caps between pin 6/7 and the supply (rather than between pin 6/7 and GND). The timers should then output a low state.

If you want to remove the relays, simply replace them with NPN transistors. A small one can be used in place of the switch, and a larger one can drive the lock coil (assuming you are driving the solenoid directly). You'll want a resistor in series with the base of both transistors. You'll also want a resistor between the base of the first transistor and GND, to reduce triggering when the input is <12V. Don't forget the diode across the coil to stop it destroying your output transistor.

If the input pulse stays on while the boot is opening, and you're happy with starting the timer when the pulse ceases, then you can remove the input switch, change the 2k2 pull-up to a pull-down, and connect the 12V pulse directly to the pull-down. If there is noise on the 12V pulse line, or it doesn't actually go properly low, there will be trouble triggering.

 

[installer69]

Hi Dougy,
thanks for that. I'll try moving the 22uF caps first. I did try replacing the switch relay with a BC547C that I had in the box but it didn't fire. I had included a resistor at the base. It may be a previously destroyed one so I'll test it after work.
The output end of the circuit doesn't drive a solenoid, it just sends an GND pulse to an ecu which triggers the closure of the boot.
The input pulse is momentary, say less than half a second. The boot takes about 3 seconds to fully open. The current circuit is powered up from the boot light which doesn't turn on until the boot is nearly fully open.
Silly question, but have I over componented the problem?

 

[installer69]

OK, moved the caps and it stopped it triggering at power up... in fact, it stopped it triggering at all.
Bought a new transistor on the way home from work and that worked. Thanks for removing one redundant bulky component. Is a 22k resistor ok at the base?

 

[dougy83]

Are the caps around the right way? The +ve of the cap connects to the supply, the negative connects to pin 6/7.

I just simulated the circuit, and it seems fine. Simulation attached (vout1 and vout2 have been scaled so that they can be seen independently).


You can replace the output relay with a transistor too. Yes, 22k is fine for base resistance.

 

[installer69]

My inexperience doesn't help. I had put the caps in series with the resistor so I moved them in parallel.
The circuit just triggered and stayed triggered on power up. I thought maybe the removal of the 2k resistors that went to earth caused this so I put them back in then the circuit didn't fore at power up but wouldn't fire at all.
I am very confused and appreciate your help.

 

[dougy83]

The 2K resistors in series with the caps aren't required. The circuit I posted (the simulation) shows where the caps should go.

If the output of the right-most 555 is active, then its pin 2 is being held low continuously by something (or repeatedly triggered, which shouldn't happen if the left-most 555 is wired correctly).

Are you testing this circuit on the bench or in the car? Put an LED (and series resistor) from the output of each 555 to GND. Have a look at what if happening. Obviously the left one should turn on for a second, then the right one for a second.

 

[installer69]

On the bench.
I may have damaged the 555s in my tinkering so I'll pick up a few fresh ones today.
Also, are the 100n caps directional?

 

[dougy83]

If the 100n caps are ceramic or film (which is likely), then they won't be polarised. Just the electrolytic (or tantalum) caps will be polarised.

 

[installer69]

Thanks.
So, just b4 work I wired back up again and wanted to report that if I use your diagram but omit the pin 6/7 to earth all functions correctly save for it going through a cycle at power up.
When I connect the earths on power up the led on 555 number 2 lights and stays on and when the trigger is applied to 555 number 1 the led on it lights and stays on.

 

[dougy83]

Pin 6/7 shouldn't be connected to earth ever; there's no such connection shown on my diagram.

There shouldn't be any cycle at startup if the capacitors have been moved to the positions shown in the diagram I posted. This was shown by the simulation output.

 

[installer69]

My silly mistake, I managed to fill in the gap where a component had been removed. Do you think that the earthing will have damaged some/all of the components? I have faithfully reproduced on a breadboard what works in the simulation so am a bit stumped.
Thank you for taking the time to help/educate.

 

[installer69]

i've replaced all the components and triple checked everything and it still goes through a trigger cycle on power up. I am completely at a loss.

 

[installer69]

I got the paisley method 1 mentioned by jpanhalt to hold a reset on power up method to work, which uses a transistor, cap and resistor.
Just need to implement your method for changing the positive pulse output of 555 number 2 to an earth pulse and I think you helped me get there. Then it is time to test in-car and start soldering.