Look at post #6 here http://forum.allaboutcircuits.com/showthread.php?t=23381

That will trigger upon application of the 12V pulse from the Lock/Unlock line.

 

Willamj, thanks for your post. No apology needed, any input is appreciated.

Whilst using the ignition to control the mirrors would be easier, it's not what I'm after. It has to tie in with the central locking system as part of what is called 'remote total closure'. My windows will close if they are open and the vehicle is deadlocked, I'd like the mirrors to fold under the same circumstances. The mirrors must then unfold again on unlocking the vehicle.

I fear using the ignition would increase the wear rate on the motor simply due to the number of times it would be active.

If your window motors are already set up to close under those circumstances, cant you just tie into the same power that is used for those motors to close your mirrors? You could use a limit switch to cut the power off to each mirror once it has reached the closed position.

 

Yes, I could, but as mentioned - the windows do not open again when the car is unlocked. The mirrors must.

 

Well I think it would be easier to design a circuit that accomplished the opening of the mirrors rather than design a circuit that handles both opening and closing.

 

My wife doesn't like me to cook. Seems that she wants me to wash the dishes after we eaten. But just cooking and eating is so much easier...

 

Well I think it would be easier to design a circuit that accomplished the opening of the mirrors rather than design a circuit that handles both opening and closing.

And what I mean by that is control the closing through the same circuit that closes the windows. Then, just design a circuit that opens the mirrors. Might prove to be easier since the mirrors need to be open when the ignition is on so you can tie in to a circuit and not have to worry about any timer circuits.

 

Look at post #6 here http://forum.allaboutcircuits.com/showthread.php?t=23381

That will trigger upon application of the 12V pulse from the Lock/Unlock line.

Well, I've been a bit stupid I think...

If I'm right then I've just found out my previous research wasn't really extensive enough as I have just built the circuit with a 556 on a breadboard. I stuck a 100pF capacitor in front of the trigger as mentioned and I got nothing.

So, to make sure I hadn't fried the 556 I made a standard circuit that which meant connecting the trigger to ground. This worked.

From this I gather I need the transistor as featured in the circuit in the above thread as well as just the capacitor. Is there any way of doing this without the transistor?

Basically the 556 needs to go Output HIGH when the Trigger goes HIGH.

 

Try using the opposite line. If they truly do switch between ground and +12, maybe you just need the opposite trigger.

 

Hmmm, I see.

Sounds like its time to test it on the loom. Can't reproduce the exact conditions on the breadboard.

If the above is the case, would I still need the 10k pull-up resistor?

EDIT: Not sure that'll work as from what I gather (and mentioned earlier) when not active they are BOTH held to ground. I could be widely off the mark though, I've spent 3 hours on it tonight and my head is starting to melt.

 

In the circuit with the transistor, a + on the base of the transistor takes the collector to ground, triggering the 555 with a negative going pulse. (the short pulse is generated by the cap charge curve) When the transistor turns off, then both ends of the cap are tied high, thus allowing it to discharge and prepare for the next trigger event.

 

In other words, I need a transistor?

This doesn't bode well, I've tried to get my head around transistors before and failed to do so. I don't know how to select an appropriate one or work out what sort of resistors I need for them. One of my original ideas was an H bridge driver instead of relays but I opted for relays for simplicity.

On the plus side, I've come across a neat way of tying the two timers in the 556 together to lock each other out, so they can't trigger simultaneously, instead of doing it with the relays. It seems a more elegant solution.

 

Instead of the transistor, you could use a CMOS logic inverter IC such as a CD4049.

 

Hmm, interesting. 6 I/Os seems a bit excessive and overkill for my circuit but it may be simpler than trying to work out transistors.

 

I'm going to order some 4069 ICs. While I'm ordering, is it worth getting some 100nF capacitors for decoupling purposes?

I've already got a 47uF decoupling cap but last night I was reading a few things on here and it was suggested a smaller cap in parallel to the electrolytic cap would be a good idea?

Any thoughts? Would 100nF be correct?

 

This is the latest circuit design, using a 556 and a 4069 as suggested. I've also made use of the lock out circuit I found for the timers rather than doing it through the relays.

One thing is that I know the decoupling capacitors should be as close to the IC pins as possible. It has just been drawn as below as I was having trouble fitting everything in. It is still a mess now!

Hopefully nothing is wrong with this, but as always, any thoughts or suggestions are appreciated.

 

First problem I see is with the 4049. You show the output and input of the unused inverters both tied to ground. Not a good thing. A LO on the input will try to force the output HI. Leave unused outputs open, but ground the unused inputs. Also may want to put pull-down resistors on the used inputs to the 4049 since the Lock/Unlock lines go open circuit when not in use, if I remember right. If they are already ground when not in use, probably not needed. Looks like you are ready to bread-board it and try it out.

 

Many thanks for that Bill.

I've now transferred the circuit to breadboard as per the above schematic (except the Inputs on the inverters are now open, the outputs are grounded and the chip is a 4069 rather than a 4049).

It doesn't work....

On connecting to a power supply (a spare lead acid car battery) I get no activity at all it seems. Connecting the trigger wire to high does nothing (even though it is inverted to pull the 556 trigger low) Neither relay is energised.

It is connected up exactly as it should be and I've buzzed out everything and it checks out OK. Not sure what could be wrong to be honest.

 

unused outputs should be open, not grounded!

Look at the data sheet. You will see active pull-up and active pull-down devices. If you ground the output and the input is open, noise may try to take the output hi, which will blow the IC.. Ground unused INPUTS, not OUTPUTS!

 

That will teach me to read things properly.

However, it still does not work. I've tried new ICs in case I had actually fried them. Still nothing

 

Do you have a scope? If so, look at the trigger inputs and outputs of the 556. Also,check the output of the 556 without the relays. Could be the relays you are using require more current than the 556 can supply.