Build it yourself, window and full throttle switch

[mcgavinz26]

I went browsing a month ago or so for instructions on how to build a window switch but didn’t find anything. After realizing that it wouldn’t be difficult I decided to make one on my own. So I have one that works now, but is a little different. It doesn’t have a shut off RPM, but it only works above an adjustable range of throttle from around 80% to full and an adjustable RPM range from about 3500 to 5000 RPMs. So it will only work when you are on the gas and when you exceed the set RPM value. Total cost = <$10.

So does anyone know of a site that tells you how to build something like this on a beginner level? This is obviously all IC components with a handful of passive parts. No microprocessor.

How interested would any of you be in something like this? I needed something like this because I have a supercharger and a boost switch is useless to me since the car makes full boost at any rpm. I plan on making a write up on how to build it. You can use it for anything too, propane, shiftlights, whatever.

 

[monte_383]

Here's a LINK to a schematic that is an adjustable TPS activated relay switch. I don't have any directions on how to build it, someone else might be able to help with that. You could build two of these circuits and wire one into the NC side of a relay for the shut off or upper limit. HTH's -Chuck

 

[Razor]

While crude,
R3 needs to be like a 1K
Transistor Q1 needs to handle the current necessary to drive the relay load.
You need a 5 volt source not listed. An LM 7805 will do. You also need filtering or the IC U1 can get zapped. I'd also run a 100K on the + input of the IC so it doesnt ever free run. D2 can be a 1n4007

Go have some fun with it.

J.

 

[mcgavinz26]

Razor, everything you said sounds right. When you say to add a 100k, you mean to use it to bridge the +input side to ground right? If you use it like it is setup now, you might run into situations where the switch will try opening the relay up if the tps is not on. Like if you had powered up the circuit but not turned on the car yet it would try opening the relay if the relay were tied to a set hot wire. I ran into the same problem when building mine and had to do that fix. That might depend on what kind of op amp you are using though.

R3 depends on what kind of LED you end up using. If you use the brighter ones that run at 3.2v and draw 20mA, then you need an R3 that fits in to this equation the closest, but larger, 8.8v / .02A = R3. Picking an arbitrary resistor will probably not net the brightest led possible and you’ll just waste power in the resistor.

This circuit is basically what a small part of my setup looks like. I’ll try to remember to give you guys a link to it when I do the write up. I’m betting there’s one person on here that might be able to get some use of it.

 

[Razor]

Ya, but if you use like a 1k resistor the LED will run cooler/longer. And the brightness still will be sufficient. The calculation calls for a 440 OHM. But this puts max current allowable on the LED. And if the battery voltage is at 14V then what... see going larger on the resistor gives added room/margin for errors.

Good luck... somebody may end up using it.

I use a similar circuit on a VCS(voltage controlled switch) I make. Tho a little more involved.