WOT microswitch

[chris davey]

So I am fitting a nitrous kit but it didn't come with a WOT microswitch. I have seen that zex have something that you wire into the signal wire from the TPS instead of a switch.

Would it be difficult to make something that would be like a relay in a way that it would only send 12v through it when the TPS signal reached close to 5v? Does Jaycar have anything like this?

Otherwise, I will just whack a microswitch under the accelerator pedal.

Thanks

Chris

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easiest way i know for you chris.

Get yourself a 4.7V zener diode. Chuck it in reverse to your TPS Signal wire. and you have a 'switch' on when ever it his 4.7V's or greater (for most cars, thats 90%+ WOT)

And then use a 5V relay or similar to switch your signal on/off.

[takai]

easiest way i know for you chris.

Get yourself a 4.7V zener diode. Chuck it in reverse to your TPS Signal wire. and you have a 'switch' on when ever it his 4.7V's or greater (for most cars, thats 90%+ WOT)

And then use a 5V relay or similar to switch your signal on/off.

Kaching, what i would have suggested exactly.

[chris davey]

So I splice into the TPS signal wire, fit the 4.7 zener diode backwards so it only lets the current past when it is greater than 4.7v.

What do you mean by 5v relay?

As in it only need a 5v signal to switch it but it will have 12v power connected to it so that 12v will be sent out when it is switched by the 5v tps signal?

Thanks.

Crap with relays if you didn't realise

[takai]

Basically a relay is a switch which turns on when it recieves an expected input.
So a 5v relay is activated when it sees 5v across 2 of the pins.

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It isn't an atypical 12V relay though, but we use it alot in electronics to a)circuit isolation, and high voltage switching. (both apply in these cases)

Autospeed Relay Article...

http://autospeed.drive.com.au/cms/A_2741/article.html

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also why not use a spare output on the microtech?

[chris davey]

I am using the output from the microtech but as you may know the tps voltage is a bit iffy. As MT only uses it for the 0-1% change to the idle map for some reason mine shows 100% when I am about 3/4 throttle. So if I activated it at 100% throttle then it would actually come on at about 3/4 throttle.

Here is a diagram I did. So if that last relay that has the TPS connected to it is a 5v relay then it will be switched when I am full throttle and let the 12v through to the solenoids.

Can you get 5v relays from normal car places or somewhere else?

[chris davey]

After reading autospeed article, I think I need to switch the 30 and 85 around on the 5v relay as the 30 and 87 are the switching part and the 85 & 86 are the coil which will hold the 12v. correct?

[takai]

Pretty much.

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yeah that diagram looks about right.

5V relay arn't typical automotive relays, you might be lucky and find a relay that will work at 5V's though. Electronics stores sell the 5V relays, i think jaycar even have a 5V/12V relay type circuit.

[chris davey]

Thanks guys +rep

Here is the final wiring diagram then for anybody elses sake.



BTW imageshack sucks the wang.

[Hen]

I'd be very hesitant to wire your TPS signal directly to a relay. Even the relay coil can draw a decent current (600mA springs to mind for normal automotive relays) and I'm not sure that the power supply to the TPS could cope with this.

I think you'd be better off using a transistor to switch the relay. I drew up a circuit below. The value of the resistor in series with the zener diode would need to be set to get the desired current flow through the transistor. The zener will need to be about 4ish volts too, since there is also a 0.7V (or maybe 1.4V, I can't remember right now) across the transistor.

Your dash switch and light can be wired in series with the 12V supply to the transistor.



I should mention that the dash switch used MUST be one of those ones with a red flick open cover, and the system will perform best if it is mounted on the steering wheel.

Hen

[Norbie]

If you decide to go the pedal-switch route, a lot of later-model auto Toyotas have a big kickdown switch mounted under the accelerator pedal (eg Aristo) so that would be perfect for what you want to do.

[chris davey]

Sorry Hen, don't have the "missile switch" just a regular on/off metal one Nice pic also. Seems to look a bit better than mine. Why would the tps be wired into the ground of the relay? Wouldn't it be the +ve side?

I went to Dick Smiths and asked for a 5v relay and they had these TINY ones about 1cm cubed so I don't think that is what I was looking for.

Thanks Norbie I may see if anyone has a front cut laying around somewhere.