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-   -   engine start / stop button question (https://www.fuelly.com/forums/f9/engine-start-stop-button-question-5452.html)

lunarhighway 07-18-2007 02:24 AM

engine start / stop button question
has anyone ever tried to make a start-stop switch? mainly for use at stoplights but it could be handy for eoc as well. since i'm about to install a radio and speakers i'll spend some time under the dashboard and need to get some supplies anyway so i might as well try this in one go. i'll place two buttons on the lower dashboard in front of the gear shifter, so i don't have to move my hand behind the steering wheel to the ignition key wich is pretty inconvenien. i like the look on peoples face when my engine seems to start the very moment when the car takes of.( wich goes surprisingly smooth actually wich makes me wonder if for a second of to the starter acts as a sort of hibrid system) although every once in a while it won't start fast enough and i look a little stupid.

yet i'd like your oppinion on what i plan to do.
one start stop button would be the ultimate cool, but since i can't see how that can be done in a simple and reliable way 'ill settle for 2 push buttons. i'd like to retain all functions of the original start key.

the starter is pretty straight forward i think, i'll just place a switch parallel to the original key swicth

the stop key poses an aditional challange. i intent to stop the engine by cutting power to the ignition (how else), most push buttons i find are of the ?make? rather han the ?break? type (making an electrical contac rather than interupting one) so i figures the only option i have is to get an additional relay that will invert the action of the swich. this system will be in line with the original system so i'm a bit concearned about safety here. it's no rocket science but still,

i'll probably be getting this relay and these buttons

and here's something resembeling a schematic of what i want to build


lunarhighway 07-18-2007 03:13 AM

ok so i looked a little colser and it shouldn't be a problem getting both normal open en normal closed buttons. yet what's the best practice, use direct contacts of work with relais? appart form maybe eliminating some wireing i see no reason to use relais.

GasSavers_Red 07-18-2007 09:10 AM

You don't have to use a relay, might want to check McMaster for parts but there are switches that "break" a connection


I'd personally use a DPDT with a center off switch. Top could be starter, middle is normal driving usage, bottom is ignition kill.

lunarhighway 07-18-2007 01:33 PM


I'd personally use a DPDT with a center off switch. Top could be starter, middle is normal driving usage, bottom is ignition kill.
that was my first thought but than i'd still have to use a relay for the ignition, as that will have to be constant on, and only interupted when the switch makes contact.... i"m not sure if that's a good idea or not

GasSavers_Red 07-18-2007 02:37 PM


Originally Posted by lunarhighway (Post 64223)
that was my first thought but than i'd still have to use a relay for the ignition, as that will have to be constant on, and only interupted when the switch makes contact.... i"m not sure if that's a good idea or not

True, forgot about that. How were you planning on tying into the ignition system? Could you use the circuit that trues off the car from the ignition cylinder?

ffvben 07-18-2007 02:38 PM

i know a few Buddy's who drag race , they have a switch to turn starter on then another for ignition. but thats on carburetors not todays fuel injected engs.

skewbe 07-18-2007 03:50 PM

I wonder if that is because the timing is so advanced that they need to build up some momentum before turning on the spark?

Bill in Houston 07-18-2007 07:10 PM

they turn on the ignition and then hit the starter.

lunarhighway 07-19-2007 03:54 AM


they turn on the ignition and then hit the starter.
i can't see a point in doing it the other way around, you'd just end up flooding the cilinders in the end no?

anyway i don't intend to build something that will allow for that, when the contacts of the starter shouldn't work either. right now i'm thinking of useing one DPDT (on)-off-(on) switch and one relay. it should be simple enough not to cause to much problems i hope. and it's be nice and ergonomic, up is on down is off. the only risk is to momentarely activate the starte while trying to shut things off.

does anyone know of a (safety) reason not to put a relay in line with the contact wire?

skewbe 07-19-2007 05:10 AM


Originally Posted by lunarhighway (Post 64339)
i can't see a point in doing it the other way around, you'd just end up flooding the cilinders in the end no?

Yah, or make a nice backfire (not that you'd notice on a dragster) if you were dumping fuel the whole time.


Originally Posted by lunarhighway (Post 64339)
...does anyone know of a (safety) reason not to put a relay in line with the contact wire?

It might be dangerous for someone untrained in your vehicle to be in it if they can activate the starter without the key. But the relay is just a good idea (I used some from a saturn for my ignition/fuel kill).

lunarhighway 07-19-2007 07:20 AM


It might be dangerous for someone untrained in your vehicle to be in it if they can activate the starter without the key
they'd also be able to turn off the ignition without the key... far more scary... but it'll be in a recess anyway so accidental or delibirate activation is less likely. and i'll most likely be so proud when i get this working i'll tell everyone what it is :D

most people are affraight to drive my car anyway, they seem to think any 20 year old car must be a wreck, most suspect my tape grillblock is there to keep the car together... lol

anyway, i hope to be able to get all the goodys i'll need this friday so i can have a look at things over the weekend.

JanGeo 07-19-2007 07:33 AM

I think you miss the point of the start button - it is smart - it will automatically start the engine and turn off the starter motor once it starts, all while either just tapping the button or holding it in.

lunarhighway 07-19-2007 08:29 AM


Originally Posted by JanGeo (Post 64366)
I think you miss the point of the start button - it is smart - it will automatically start the engine and turn off the starter motor once it starts, all while either just tapping the button or holding it in.

in your car maybe, but i know that when i turn the key one notch forward with the engine on there's a nasty screaching noise comming fom under the hood... had that a couple of times while i thought i was EOC ing but the engine was still on because i turned the ignition back on to soon while it was still spinning... doing a keystart than did not sound so well. that said my car usually starts pretty well especially when it's warm so a small nudge against te switch should be enough to fire it up again. this car's 20 years old so i should think some things have evolved. although i like the solid straightforward construction of it

Gary Palmer 07-19-2007 09:35 AM

Lunarhighway: I think the point JanGeo was making might have been missed. Your correct that if you turn the starter switch the notch foward, the starter engages and grinds teeth on the flywheel. I think the switch JanGeo is talking about is electrically disabled, when the car is running, so that even if you toggle the switch, the starter won't engage. It makes it so the starter will only engage, if the car is not running, which is a little different behavior than the key switch.

As far as your cutoff and so forth go, you don't need to use a relay unless your using it to actually switch the power to a device that uses a lot of power. For example you could use a switch to control the starter relay, but you would not want to use a switch to power the starter.

If you do use switchs, I strongly recommend you put a 0.01 micro farad capacitor across the switch contact connections. It will help keep the switch contact points from arcing and burning themselves out. You can run it without the capacitors, but the switch will wear out, fairly quickly and you'll have to replace it.

I have a switch on my car, for cutting off the power to the injectors. It works fine, although I get a cel when I use it. I haven't gotten a start switch wired in, yet, although it is planned.

My only warning is that if you have the kill switch, like I do, it is easy for someone, like my kids, to fiddle around playing driving in the car and fliping the switch, without me knowing it. I spent a good deal of time tracking down why I couldn't get the blinkin car to restart.

lunarhighway 07-19-2007 03:24 PM

sorry JanGeo if i came across rude. i may not always understand everything correctly, the system you describe would be more elegant than what i'm planning to build.
but all i need is something that replicates the engine on / engine off function of the key in a more accessible position. i don't need anything else unless safety dicates it.

as far as acidently opperating the system by passengers goes...i'll let you all in on a little secret. it so happens that directly behind my gear shifter there's a little ash tray/garbage bin, that folds open . it looks like it's never been used, and i don't smoke, but it's ideally placed to put down a sigaret and free your hand to shift the gears. there's even a tiny light in it when the main lights are on.... perfect spot for a switch i'd say. when it's not needed i can just stow it and noone will notice it's there or be able to interfere with it

i initially thought i'd need 2 buttons but i figure this switch combined with one relay can do the trick.
it will always return to the center neutral position and won't do anything without the key so i think i'm safe there as far as kid's interfearance goes (there probably won't be any kids for the next few years so that helps too ;) )
i can set it up so that "up" is the starter and "down" is the ignition cutoff, same as what i do with the key now.

thanx for the tip on the capacitors Gary Palmer , i didn't realise sparks would be that much of an issue. i assume that all wires leading from the key swith are just part of the 12V system and drive relays to power the starter and the ignition opperating on a higher voltage but 12V should be enough to make some nasty little sparks i guess. should i put a capasitor across the relay as i assume there's still a mechanical switch in there?

rh77 07-19-2007 03:34 PM

good thread
As an automatic driver, I'd love to have one attached to the shifter so engine kill can be done in neutral with one hand on the selector, and same for restart and "D" engagement.

If it's in a "public place" in the car, maybe you could wire it up with a lockout or bypass at the flip of a switch, so it doesn't get monkeyed-with when you don't want it to.

But yeah, even with a key-start system, I've ground on the starter with the engine running. It happens most right after cold start when the RPMs are up and I fail to take a quick glance of the tach to see that the engine was still rotating and fired back up at key-on. It's easy to be hyper-vigilant with EOC and reading other traffic, and not on instrumentation :rolleyes: .


skewbe 07-19-2007 04:10 PM

I like a golfcart type approach (it just isn't on the top of my priorities at the moment)

IF the clutch is all the way in
AND the throttle is significantly off idle
AND the ignition is on
AND the engine is not running
THEN start the engine (needs to know when to stop starting also)

skip the clutch bit on an automatic maybe.

lunarhighway 07-20-2007 01:10 AM

i quess i should know this since i've studdiet electronics for 2 years but most of what i (should) have learned there is shamefully gathering dust somewhere in the back of my mind.

does anyone know how to calculate what capacity the capacitors should be that go over the switches, i did some brief research on the subject and it seems to be a very good idea to install them so i'll give it a go. yet i'm not sure what capacitors to get though (i'll probably get them today after work), does it matter much what capacity they are or do i have a certain margin 0,01µF seems fairly low ? if i understand the way they work correctly it shouldn't matter that much. also what's the importance of their voltage rating is that max voltage, if so anything above 12v should do rihght, as they all seem to be on the high side.

anyway any help will be greatly appreciated, capacitors are interesting but i do know they tend to blow up (elcos at least) when you attach them the wrong way round. needless to say lot's of these things where “accidently” blown up in class. i'm not intending to get elco's as i don't need their capacity.

lunarhighway 07-27-2007 11:17 AM

I've got the goods!!! :D
most of them i should think:

as mentioned it my LED question thread i finally decided to go for a dual button system.i was considdering a single paddle swich opperation, wich i could still make.

i'm building this into my fold out garbage bin, but since i want to be able to stow the bin i can't have anything projecting beyond the edges so buttons where more handy, plus the LED's will add a cool effect, and aid at night.

the people in the shop where very helpfull, when i got the switches the guy mentioned i'd need resistors asked me what voltage i'd use and simply grabed two resistors from a bin. according to the color code they're 562 ohm, 5% tolerance, that's about what i'd calculated... should give me about 18mA so that looks fine.

i also got a little buzzer wich will act as a powersaving device by alerting me when i've left my headligths on. apparently this was an option 20 yeas ago.
my car does turn of the headlights automaticly, but only after about 2 hours...by draining the battery. :rolleyes:
here's a some relays i found in the attic... they're probably pretty old, but they still work fine and the left one is even so kind to tell you what's inside! how thoughtfull. i plan to use this as a breaker swich for the ignition, it will be driven by the stop switch.... guess wich color i'll use for that one.

here's the garbage bin (wich i doubt the privious owner even found by the look of it!...it looks factory fresh on the inside...i feel a bit sorry to drill holes trough it) i'll fabricate some sort of front plate to accept the buttons.

stay tuned for more pictures of this stuf being put together, silly questions, and perhaps some explosions...

skewbe 07-27-2007 05:19 PM

Might I suggest putting the switches on the stick shift? It's a very "handy" place.


lunarhighway 07-28-2007 09:54 AM

good sugestion, yet i think it would pose a few difficulies in my case.

in order to switch to reverse there's some sort of ring below the knob of the shifter that you need to pull up that would interfere with the wires.

switching gears on my car also reaquires quite some force for some gears too so i'd rather keep it clean, i woudn't want tot hurt myself on the button, or accidently activate it.

anyway i'm off to the car to start working on the system! i'll take some pictures!

lunarhighway 07-29-2007 06:57 AM

pictures of the progress

resistors soldered to the buttons
we have red light!
we have green light!
wires connected to the relay
click click click.... :)
i've cut some plastic out of the lid of an icecream box to make the backingplate for the buttons, the grey plastic came from a frisbee.

rh77 07-29-2007 07:28 AM

Very Nice -- looks good so far :thumbup:


lunarhighway 08-09-2007 01:32 PM

more progress on the buttons, basic setup and internal wireing of the system is complete, now it just needs to be hooked up to the cars electric system.

here's the standard center console. (pretty 80's ...with mechanical climate controle :D )
however there's more to it than meets the eye!

step 1
drill a hole in the back of the ashtrey (the plastic was very hard and i should have used progressive drill sizes rather than try to do it in one go, as a result a piece of plastic snapped out....fortunately not to big)

make a hole in the ashtrey resess this plastic was softer and after drilling 6 little holes a nice rectangle could be filed out

after trying many things i setteled for a cardboard insert... easy to work with, cheap strong.... the top cover of my dashboard as well as the interior roof cover are made of some sort of car-like matherial as well... pressed to shape and covered with a leather like film, it's actually quite a warm and strong matherial.

step 4
i gave the cardboard incert a coat of underbody spray (for lack of regular black paint) gave it a gloss coat once dry and intalled all the buttons and the wireing at the back. i think the finish matches the rest of the interior quite well. the buttons are illuminated and the ashtry already had a little light bulb in it. so they will stand out :)

now i only need to incert a relay to cut power to the ignition and bridge the original starter key with the green button.

egnorant 09-19-2007 08:59 PM

Being cheap I used a lot of factory parts.
When my keyswitch fell out in my Escort I used a headlight switch from a mid to late 80s T-bird.
This gave me an accessory possition and a run position and looks factory in the spot where the switch for the rear defroster should be.
Has plenty of apacity and enough poles that I didn't need to double up any wires.
Starter is a simple momentary switch that only had power when the ignition was in run and the clutch is depressed.
My buddy liked mine and built his with the original switch in the console with a cable and a slider on the shifter. click one is assesory, click 2 is run and pull all the way up is starter. He can control it with his middle finger while his hand is on the shifter.

Its just wiring, determine your dream and then make it work!


lunarhighway 09-25-2007 06:33 AM


Its just wiring, determine your dream and then make it work!
that's right... it's really much more practical and safe than what i did before


i turn the key on and off
but i'm laaaazy... i figured the effort of having to reach for the key and having to twist it eeeeeverytime would ammount to a far greater overall effort than building this thing and just having to extend my finger from that point on....
most inovations are there to facilitate lazyness ;)

bearleener 09-26-2007 06:58 AM

Start/stop buttons
Nice project, lunarhighway!
Coincidentally I'm doing just about the same thing on my 1996 VW Golf.
Further coincidentally I've also accommodated my buttons in the console ashtray, though not as elegantly as you.
Ultimately I want to have the engine shut off automatically whenever I'm coasting (down to idle speed; my engine only does this above 1700 RPM), as well as auto start/stop at stoplights (using the BMW Efficient Dynamics algorithm -- if gear in neutral and clutch pedal released, shut off; when clutch touched, restart). I've bought a microcontroller to do this but I've just started to learn how to program it.
In the meantime I've been switching manually, simulating the algorithm that the microcontroller should do. I just installed the starter button a few days ago so I don't have any results yet, but it's very convenient.
With my last tankful of gas using only the coast shutoff switch my fuel economy improved from 6.9 to 6.2 l/100km, about 10% improvement (though there may have been other factors contributing)! So that's good motivation.
Acting on a tip from the owner of Black Fly #2 Firefly, I do the engine cut by interrupting the signal coming from the Hall transducer mounted on the distributor, which normally tells the ECU when cylinder #1 is at top dead center. If there's no signal the ECU thinks the engine is off, shutting off sparks and injector. A side effect is that the tachometer gauge goes to zero and the oil pressure light comes on (though the oil pump is mechanical and still running -- I hope).
So keep it up -- your friends will be impressed that you can teach your old car new tricks!

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