Car Relay Question - Momentary Button Activates Second Switch, Deactivates Itself Until Second Switch Activated??

Thread Starter

Daniel.is.here

Joined May 17, 2022
5
I’m never one to stop at “simple,” but often find myself overthinking things.

MY QUEST: I have placed a simple keyed switch along the ground wire to the transmission shift interlock. I want to be able to leave my car on while I run out for brief moments and not worry about someone seeing opportunity. This simple implementation works, as the transmission will not budge when the switch opens the ground line. However, the key is cumbersome to slide into the mechanism, and so I have ordered an RFID access system that offers a relay that can open a circuit on a timer, momentarily, or “flip flop.”
My ultimate vision is to have a simple momentary button that I can press which will then break the circuit to the shift interlock until the RFID access system senses a fob and allows the circuit to become whole again. It seems much easier to press a button and hop out of the car rather than fumble for the key and twist it and then remove it, etc.

MY QUESTION: How would I go about wiring a circuit up such as this? Assuming I don’t use the RFID access system and instead decide to have one momentary switch when pressed then requires another switch (hidden) to be pressed or toggled to close the circuit?

(In essence, if someone were to see me press one button and then they themselves decide to push the same button, they would achieve nothing unless they find the second switch - which when pressed would then re-activate the shift interlock and the first button.)
 

Ian0

Joined Aug 7, 2020
5,097
Why don't you just stop the engine to reduce fuel costs and pollution? If it doesn't start well, get a new starter motor.
 

Thread Starter

Daniel.is.here

Joined May 17, 2022
5
Why don't you just stop the engine to reduce fuel costs and pollution? If it doesn't start well, get a new starter motor.
It strikes me as a bit more cumbersome on the engine to turn it off then turn it back on multiple times.

I had also asked the question because I am intrigued by electricity and had been hoping for someone who has a firm grasp of circuitry to outline a method I had been overlooking because I’m getting myself stuck on having a second relay providing the first relay with power through the nc pin but then when that relay is activated and sends power to the second relay, which would likely be a latching relay, it seems to pan out until I try and draw it out considering the break in the ground rather than a supply of 12v.

I do, however, appreciate you taking the time to speak about matters of the environment.
 
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Thread Starter

Daniel.is.here

Joined May 17, 2022
5
Sounds like a simple flip-flop type circuit will do what you want.
I imagine so, however, I’m having difficulty visualizing the circuitry. A momentary switch would effect the “flip” but I don’t want it to effect the “flop.” The “flip” would need to remove power from the original source (the momentary switch) and open the shift interlock ground, and then provide power to another switch, which when pressed then returns power to the original button and restores continuity to the ground wire.
 

Tonyr1084

Joined Sep 24, 2015
6,884
Simple. Assuming the Trans Lock requires 12V; a relay configured using DPDT 12V:

Press S1 while engine running and relay K1 will lock itself ON. Press S2 and the relay will unlatch. D2 is a snubber to prevent any potential damage to any circuits that may be susceptible to voltage spikes. D1 prevents the relay from back feeding power to the vehicle electronics.
1652881255161.png
Using a Flip Flop circuit would work too. However, depending on the FF it could be susceptible to voltage spikes. Using the SET pin - drivien high will set Q output high, locking the transmission. Using the RESET pin - driven high will set Q output low, unlocking the transmission. Assuming the current required for the Trans Lock will not exceed the output specs of the FF. [edit] What state will Q be in when the car is started? Probably low, but I don't know that for sure. You may have to unlock the transmission every time you start the vehicle. The relay? Always off until you turn it on. No need to worry about specs of a FF or use of a high output transistor or MOSFET. [end edit]

My dreamed of anti-theft device is a removable gas pedal. Where are you going to go that you can idle to? How far can you get idling down a level street? Up hill? Forget about it.
 
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Reloadron

Joined Jan 15, 2015
6,584
All you are doing is making or breaking a ground. There are plenty of key fob operated relay boards out there. Anything from 4 channel down to a single channel. This is a 4 channel example which runs on a 12 volt system. Real simple would be a SPST common switch (kill switch) hidden under dash or anywhere.

Ron
 

Thread Starter

Daniel.is.here

Joined May 17, 2022
5
All you are doing is making or breaking a ground. There are plenty of key fob operated relay boards out there. Anything from 4 channel down to a single channel. This is a 4 channel example which runs on a 12 volt system. Real simple would be a SPST common switch (kill switch) hidden under dash or anywhere.

Ron
I appreciate the idea, however I really dislike button key fobs. I’m always wondering whether to pushed the button or didn’t or if I accidentally unlocked my car when I was out of earshot … an rfid fob, on the other hand, no buttons.
This desire of mine to have one button which activates another button that must be pressed to proceed, it’s merely preferential. No, I probably don’t need any sort of kill switch as is, or I could just turn the car off and take the keys with me if I’m hopping out for brief moments, but why beat down the seedlings of curiosity by bludgeoning it with “why bother?” I know I’m no genius, so I can’t speak with an enlightened perspective, but how many of the brightest minds out there today do you think were people who shrugged their shoulders when asked a question and then turned their focus back to the football game?
 

Reloadron

Joined Jan 15, 2015
6,584
I appreciate the idea, however I really dislike button key fobs. I’m always wondering whether to pushed the button or didn’t or if I accidentally unlocked my car when I was out of earshot … an rfid fob, on the other hand, no buttons.
This desire of mine to have one button which activates another button that must be pressed to proceed, it’s merely preferential. No, I probably don’t need any sort of kill switch as is, or I could just turn the car off and take the keys with me if I’m hopping out for brief moments, but why beat down the seedlings of curiosity by bludgeoning it with “why bother?” I know I’m no genius, so I can’t speak with an enlightened perspective, but how many of the brightest minds out there today do you think were people who shrugged their shoulders when asked a question and then turned their focus back to the football game?
Well alrighty then. I mentioned a key fob remote based on where you mentioned:
My ultimate vision is to have a simple momentary button that I can press which will then break the circuit to the shift interlock until the RFID access system senses a fob and allows the circuit to become whole again. It seems much easier to press a button and hop out of the car rather than fumble for the key and twist it and then remove it, etc.
That's why I even mentioned a remote fob (wireless approach). You can use a simple hidden switch or make this as high tech and complex as you want. You have a shift interlock. It can be enabled or disabled. When ground is made (logic low) the system is enabled, remove ground and the system is disabled. If you go with a RFID reader you will need a RFID card to place in proximity of the reader. Much like new cars where you don't need the key in the ignition, just in close proximity to the reader. You want simple buttons? Just use a simple relay latching circuit as was presented. You can do this with likely a dozen different designs ranging from simple to complex.

Ron
 

Thread Starter

Daniel.is.here

Joined May 17, 2022
5
Well alrighty then. I mentioned a key fob remote based on where you mentioned:

That's why I even mentioned a remote fob (wireless approach). You can use a simple hidden switch or make this as high tech and complex as you want. You have a shift interlock. It can be enabled or disabled. When ground is made (logic low) the system is enabled, remove ground and the system is disabled. If you go with a RFID reader you will need a RFID card to place in proximity of the reader. Much like new cars where you don't need the key in the ignition, just in close proximity to the reader. You want simple buttons? Just use a simple relay latching circuit as was presented. You can do this with likely a dozen different designs ranging from simple to complex.

Ron
Reading back through my response to you, I apologize if it sounded like I was directing an attack toward you; I wasn’t. Too many people provide responses stating why your idea is dumb and it gets annoying when your excitement flops over when the page finally loads after you get a notification. Oftentimes, people will present a simple solution that may have been completely unknown to the author of the question, and I do appreciate all of your input.
Part of the intrigue I get from electricity is the ability to be complex or simple, and since I’ve got a (very) marginal understanding of simple relay switches, my curiosity of course complex me to deepen that comprehension by incorporating multiple relays and switches and solving the simple problem of how to open or close a circuit using conventional and unconventional means.
 

Reloadron

Joined Jan 15, 2015
6,584
Reading back through my response to you, I apologize if it sounded like I was directing an attack toward you; I wasn’t. Too many people provide responses stating why your idea is dumb and it gets annoying when your excitement flops over when the page finally loads after you get a notification. Oftentimes, people will present a simple solution that may have been completely unknown to the author of the question, and I do appreciate all of your input.
Part of the intrigue I get from electricity is the ability to be complex or simple, and since I’ve got a (very) marginal understanding of simple relay switches, my curiosity of course complex me to deepen that comprehension by incorporating multiple relays and switches and solving the simple problem of how to open or close a circuit using conventional and unconventional means.
No problem at all and no offense taken here. I can appreciate enthusiasm and wanting to do something in a more interesting fashion than just a simple approach. Really matters not to me if you choose to leave an engine running or shut it off either. With a focus on your question and only your question you only need to make or break a ground connection and that's all. So this can be done any of several ways. If you see a solution you like here from anyone it can be run with. Matter of fact and off topic I found out I can buy an RFID reader for about $45 USD and read the chip in my dog. :) Still need to get my other dog chipped.

Ron
 

vu2nan

Joined Sep 11, 2014
232
Hi Daniel,

An automotive latching relay may be used.

2.png 1.png

Two momentary push buttons enable or disable the transmission shift, using the 20 A contact (3 - 5).

Nandu.
 
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Tonyr1084

Joined Sep 24, 2015
6,884
One reason why I would opt for the simple approach is akin to something Engineer Montgomery Scott said to then Admiral Kirk concerning the star ship Excelsior. "The fancier the plumbing - the easier it is to stop up the drain." Point made is that when a system is overly complex it can suffer failure from many points. An RFID reader - while it sounds simple - may require you place something NEAR that reader. That's more complex and just as laborious as pushing a button while pushing a button is far simpler. Those fobs that are detected by a car that allows access and operation of the vehicle are not like RFID readers that I'm aware of. And with more complexity - comes more opportunity for you to get stranded somewhere because your system refuses to unlock.

Cell phones have facial recognition. Imagine having that on your car. You are the only one who can access or operate it. Challenges are presented and you choose to rise to the occasion. That's fine. We all understand the desire to build something the way we envision it. Sometimes it's not so wise because of other possible issues that can arise. Sometimes it's unwise because it may present unnecessary dangers. Here's a highly unlikely scenario - you're driving across railroad tracks and suddenly the transmission locks up because some battery goes dead and now you're stuck with a vehicle that can't be moved off the tracks. We see the train approaching. Why don't you? In my house there's a very old and extremely proven track record for this technology - it's called a light switch. Works damn near every time. And if it fails you're not in any danger.

Your post has gotten me thinking of doing the same thing. I just need to see if my vehicle is so equipped with a transmission interlock. There is probably a market for such a device so that people here where I live in the winter time can start their vehicle and then leave it running in their driveway while it warms up and melts snow and ice off the windshield. As it is people do that and their cars are getting stollen because of sheer opportunity for an easy theft. And sometimes kids are in a back seat at a convenience store and they go for an unexpected ride. I can't imagine how the parents must feel when that happens, but I bet they wish they would have had a trans-lock system.

Security systems that are well known can be defeated if you know what you're working with. But a thief isn't interested in taking the time to defeat a home made system that can take them several minutes to hours to defeat. They'll just go grab the next vehicle. That's why kill switches have been so popular. But thieves are smart enough to find them quickly. Something like your proposal would baffle them long enough to encourage them to go elsewhere with their theft-craft. But there's been good reason for the mantra "Keep It Simple Stupid!" And no - I'm not saying you're unintelligent. I prefer to call it "Keep It Stupidly Simple." Not insulting and makes a better point. Simplicity is the key. Otherwise I'd have facial recognition on my vehicles. That way only I (or my twin) could access my vehicles.
 

Reloadron

Joined Jan 15, 2015
6,584
Your post has gotten me thinking of doing the same thing. I just need to see if my vehicle is so equipped with a transmission interlock. There is probably a market for such a device so that people here where I live in the winter time can start their vehicle and then leave it running in their driveway while it warms up and melts snow and ice off the windshield.
My old 2007 Yukon Denali had remote start. The truck would start, warm up nicely. However, the doors were locked and even if someone did get in you had to have a foot on the brake pedal to shift the transmission and unless the key was inserted and ignition turned on the truck would shut down as soon as you placed a foot on the brake. That was all by design back in 2007. On the key fob you just tapped LOCK three times and the truck would auto start. Nice to have when it was sub freezing outside and in NE Ohio we had plenty of cold. That was factory.

Ron
 
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