Help with Automotive Project Please.

[soundcatcher]

I'm working on a project that is pushing my knowledge to it's limits. I'm totally self taught and I pick up knowledge as I encounter stuff that I don't' understand or tackle new challenges. On this occasion I've come a bit un-stuck.

I'ts good old auto-electrics this time that has me tearing what little hair I have left out! I have a custom car that has solenoid doors. I decided that I wanted something a little bit different so I have decided to use a Capacitance Switch to trigger the doors to open, rather than use a pushbutton or remote control. This switch works fine by iteself but when you trigger an unrelated device like the electric windows, a spike gets sent back up the powerline and triggers the door switch and they then get stuck in a loop and go crazy! Not great if you're driving down the road and need to adjust your window and the doors open!

So after a bit of searching I think I have 1 solution... Unless you guys can think of a better one. I'm thinking about using a transient voltage suppressor across the sensor circuit to hopefully stop the unwanted triggering from happening.

So far so good but at this point I don't know which one to choose and I don't know how to work out or where to measure to find the parameters that will narrow down the choices?

Does anyone have any experience with TVS and can you please guide me gently in the right direction as to what to do. I've read dozens of articles, but as yet they all say the same thing, but don't give me the laymens version so that I can grab a meter and start to work it out? I have a feeling that once It's been explained I will kick myself. But at the moment I feel as though I am banging my head against the wall on this one.

Many thanks in advance...

Andy

 

[poor mystic]

Hi there Soundcatcher
have you seen the wikipedia article? https://secure.wikimedia.org/wikipedia/en/wiki/Transient_voltage_suppression_diode
I've never used a TVS myself either, but I thought the article was easy to read and I wonder how you like it. It's a diagnostic article... enables us to diagnose your understanding! (I'd be surprised if you're far behind, it just doesn't seem likely that you are any kind of slow.)
Which bit if any do you have trouble with please?

 

[daddles]

One obvious thought is to not allow the door solenoids to operate if the transmission isn't in, say, park.

Another thought is to measure the spike that is causing the problem, then design a fix for something 5 times that much. This is where the real engineering is in complex systems: finding and fixing these corner cases.

 

[poor mystic]

AIso, I wonder whether a bifilar inductor in the power leads to the circuit board might be a good solution. This is an inductor which consists of both power leads wound together on a ferrite stick so that spikes cancel out.

 

[soundcatcher]

Hiya, things have moved on a bit since I posted this question up earlier. I kind of spread bet the problem over a couple of forums and this one came up trumps and has suggested that it might not be a TVS that I need after all. Possibly just some smoothing capacitors in the right places. So that's where things have got to for now.

I've just got a load of components ordered on ebay as it's more cost effective these days than using online retailers.

So now I'm eagerly either awaiting the components to arrive or somebody to give me more information or a different solution to think about....

 

[soundcatcher]

One obvious thought is to not allow the door solenoids to operate if the transmission isn't in, say, park.

Interesting idea. I did think about that solution, but there were too many variables of situations where I would want to be able to use the widows and have the doors operational whilst not necessarily wanting to open them

Another thought is to measure the spike that is causing the problem, then design a fix for something 5 times that much. This is where the real engineering is in complex systems: finding and fixing these corner cases.

Yes, well that's where my knowledge runs out.....I only wish I had the talent to do such things...

 

[soundcatcher]

Hi folks. So I've had a bit of a break on this project whilst I opened our new shop. So now things have got a little easier on the time side I'm getting back into the swing of problem solving.

I've fixed the retriggering by using a non retriggerable timer circuit after the sensor circuit. The next issue I have is that the negative power lead on the sensor circuit is acting like a trigger when there's a spike from another system or even if you touch the connector where it is fitted to an earth tab.

So I'm back asking for help again...... I think if I had a 12v dc to 12v dc something that isolates the + & - inputs from the + & - outputs so that spikes cannot travel across from the power source to the circuit that'll solve that issue.

Does such a thing exist or how do I go about building such a thing???

Thanks in advance...Andy