Hello all, newbie here looking for some help on a little project.

My car has a total closure circuit that closes all the windows when you deadlock using the key remote. I also have folding mirrors but the two are not combined. The mirrors only fold on a switch on the door. I'm looking to make a circuit that will fold the mirrors in when the deadlocking is activated. As the lock signal is momentary, the circuit must have power for 3 seconds after the signal. They must also unfold when the car is unlocked.

At first I thought about using relays, then it was suggested to me to use transistors - they are smaller and cheaper. I've come up with the following circuit...

My apologies for the screenshot but that is the only way I could save it to post on here. Hopefully you can see how it would work. The two changeover switches are the closest thing that the software I'm using has to what the car uses but hopefully they give the general idea.

My questions are as follows...

1. Will this circuit work?
2. What type of diode will D1 and D2 need to be?
3. What values will R1, R2, C1 and C2 require to keep the circuit powered for 3 seconds after the initial lock signal.
4. I need a way of isolating the circuit when the ignition is on so that mirrors cannot be folded by accidental locking. I think this would need to be between my circuit and the original locking circuit. The circuit also must not interfere with the original functions of the mirror switch and central locking system. How do I do this?
5. Will the transistors affect the voltage at the mirror motor? It needs to be 12v

I do hope I've explained that well enough, my apologies for waffling. Any help is very much appreciated.

Thanks

 

1. Probably not ... for starters you need a current limit resistor in the base of all transistors.
2&3 You probably need a complete rethink although the full bridge driver is a good way to go your control needs some work.
4 .... build this in as a control function, think monostable timing and logic to drive the bridge.
5 Yes ... you will always have a voltage drop but you will have plenty of scope to play with I suspect.

Also considder what will happen if the switch is operated at the same time as the circuit you suggest, a dead short is possible right now.

Just my opinion but I would considder driving the mirrors with your new circuit all the time and making the existing switch a control input of the circuit, that way no conflicts are possible on the power side of things.

If you arn't happy with power transistors you could always uae a couple of relays to drive the motors and control them with your new logic, incorporating the input from the existing switches on the control side.

A 74123 is a pare of edge triggered monostables which would be ideal for sensing lock / unlock and producing a 3s(ish) pulse, there are other none TTL equivalents but I cant remember the numbers.

All you would need after that would be 'and' and 'not' gates feeding the drive circuit, whever one you go with.
Hope that helps
Al

 

Thanks for your help.

It seems the transistor idea may become too complicated for my limited knowledge. Relays may be the way to go.

This was the original design which, I must add, is not my work

I could see how this would fold the mirrors on locking, but I cannot work out how it would unfold them on unlocking. Any ideas? Note, the wires from the switch to the motor are cut and when the relays are at rest, the switch can operate the motor.

 

It wouldnt but you could easily do something simmilar that would.
I can draw it if it will help but I would need to know how the mirror switch is wired now.

Is the switch two position, open / fold, and do the mirrors stop mid way if you take your finger off it?

Please discribe to poeration you have now and if possible the existing wiring.

Al

 

Strange, as the person who designed that circuit says that they do unfold.

The original set up looks like this. The mirror switch is misleading though as it appears to have a rest position when it seems it doesn't for folding purposes. I'll come to that in a second.

The switch itself is a rotary switch. Turn it to 6 o'clock and the mirrors fold. Turn it away from 6 o'clock and they unfold. It doesn't matter if the switch is turned clockwise or anti-clockwise. The mirrors fold and unfold and soon as it leaves the appropriate position, not when it reaches the next one if that makes sense. The switch also stays in the position its turned which makes it seem the rest position in the diagram is misleading.

Its all done inside on a circular shaped board with tracks on. The switch operates a plastic disk that has metal contacts on which bridges parts of these tracks.

Hope that is fairly clear.

 

Building on the original relay circuit that doesn't seem to unfold on unlocking, I've come up with this...

Why I didn't think of that sooner I do not know but your help has made me think of things I initially hadn't and nudged me in this direction. This should work shouldn't it? Its the easiest way I can currently think of that performs the functions it needs to as well as avoiding a dead short. I don't know, there may be something easier?

 

I've realised that even the previous circuit has a flaw and there is still a trap in there for a short as the switch doesn't have a rest position.

I can't figure out how to get round this one.

 

Anyone? I'm stuck on this one.

 

The mirror motors must have limit switches built in, either that or the feed from the switch to the mirrors isn’t actually the power.
In either case your drawing indicates that the switch provides a permanent feed to the motors and reverses it when you move the switch from fold to unfold.

In the attached drawing relay 4 is responsible for reversing the feed to the mirrors but the existing mirror switch stays in circuit so the effect is to reverse its operation IE Fold becomes unfold.

Relay 4 will be de-energised when the car is locked so it should be connected with the mirror feed reversed in this condition. IE the switch is set to unfold, the relay is off and the mirrors are folded.

Relay 1, and its associated diode detect unlock, closing only when the locking motors are running.

Relay 2, and its associated diode detect lock, closing only when the locking motors are running.

Relay 3 detects ignition, its normally closed contacts disabling relays 1 and 2 when the ignition is on.

The system will work as follows ….

When the ignition is on locking or unlocking will have no effect because RLA3 is on disabling RLA1 and RLA2.

Assuming the ignition is off …..

Unlocking the car will cause RLA1 to pull in for as long as the locking motors are driving.
Because RLA2 is de-energised RLA4 will pull in and remain there, latch, even when RLA1 opens because one of its own contacts is in parallel with RLA1’s contact.
RLA4 being energised will reverse the polarity of the mirror motor control and, assuming they were folded to begin with, the mirrors will unfold.

Locking the car will cause RLA2 to pull in for as long as the locking motors are driving.
This will interrupt the supply to RLA4 causing it to unlatch.
RLA4 being de-energised will reverse the polarity of the mirror motor and, assuming they were unfolded to begin with, the mirrors will fold.

Whilst RLA4 is energised (Unlocked state) the mirrors will work as they should, allowing them to be folded or unfolded from the switch.
Whilst RLA4 is de-energised (Locked state) the mirrors will still respond to the switch but the function of the switch will be reversed.

Hope that helps
Al

 

Interesting. Many thanks for your time. I do appreciate it.

As you posted I thought of perhaps another way. Could I use the previous circuit I posted, containing two DPDT relays, one for locking, one for unlocking and remove the SPDT ignition fed relay. Then add a DPDT relay with an ignition switched feed between the mirror switch and the motor.

When the ignition is on, the original circuit is in use and my mirror folding circuit is isolated from the original circuit. When the ignition is off, the relay de-energises and isolates the switch from the motor and connects the motor to my circuit. This avoids any conflicts and shorts and fulfils my original idea to retain the switch function and have no effect when the ignition is on.

The only thing I can't work out on this one or your circuit is the value of capacitor I would need to power relay for 3 seconds and if the central locking signal would be enough to charge it.

 

Can anyone help with capacitor values? I've researched RC circuits but cannot get my head around what cap I need. Am I right in saying it will need to be placed in parallel with the relay coil? I understand coil resistance is important too.

So I need a cap that will charge in less than a second (from the central locking signal which is momentary) and then discharge through the relay coil, keeping it powered for 3 seconds which I believe would require a resistor?. Coil resistance is around 280ohm and the source voltage is 12v. How would I work out what I need from this and where to place the resistor?

 

My circuit dosnt need a capacitor because RLA4 is latching, in that it hold its self in, via RLA2.

I did it that way so it mimics the function of the existing mirror switch.
If, as I suspect from your description, the mirrors contain some sort of circuit with its own power supply, then the switch is simply a signal and may need to be constant, as it is now, rather than a pulse.

In your post about the switch you said the mirrors move befoer the switch is all the way across ..... dosn't sound like a simple feed connected to a motor.

RE caps if you go that way .... There will be formulas that will tell you how much energy the cap will hols at any given voltage but given that the current through the relay coil will vary with voltage and you probably wont find data on the precise voltage at which the relay will drop out I would recomend simply trying a few.

You dont need resistors and I would strat with circa 2000uF remember you can simply add aditional parallel caps to increese the value and hold the relay longer.

The correct way to go would be a little timing circuit, edge triggered, but then you didnt want to be mucking with electronics as I recall.

Caps on relays work, BUT they will not be very consistant so you need to build in a asignificant margn for error. They also tend to cause arching when the relay opens, because it is doing it slowly, but that is probably not going to be too much of a problem given your light load.
Al

Al

 

Thank you very much for your help.

I guess this just leaves me to build the circuit and experiment and see if it works.

Much appreciated.

 

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