simple switch trigger?

I'm really at a lost to this problem. I have a 2008 Santa FE with seat warmers. I decided I wanted to trigger the seat warmers from an AUX channel with my viper 5901. Simple enough right? I was able to tap into the two switches (left and right seat), and I'm able to take either one of those wires, ground it to the chassis and the switch triggers just like I pressed it. So I have the correct wire to trigger the seat warmer. Now here is the problem. I can't even get one to work right. If I hook one up to the AUX channel, it wont trigger. If I just tap the wire to the chassis to ground it, it triggers no problem every time. So this has to be a negative pulse trigger right? Now because I wanted to turn both on at once I figured I would need two diodes, so the physical buttons don't ground each other out. Enter weird problem number 2. If I tap the seat warmer wire to the chassis it triggers, if I put a diode in-line it no longer triggers. Yes I know a diode has to go in a certain direction, whenever a diode is in-line it will not trigger the seat warmer. So even if I get the AUX channel to work, I'll still have the issue that a diode will mess it up. Diodes tried, 1N4001,1N4004,1N4007. Which is really confusing to me. I also hooked up a DMM, from the lead I made to the seat warmer switch, here are the values I got. Without diode 1N4001 V: 4.7 A: 0.94ma Ohms: nothing, 0 With diode 1N4001 V: 4.43 A: 0.81ma Ohms: nothing, 0 What am I doing wrong? why does grounding to the chassis work fine, but when I add in the diode it stops working? It also looks like the switch is using 5V, it's a momentary switch, press turns on high, press again turns on low, press again to turn off seat warmer. Does the 5V mean I can't use the negative AUX channel, I thought negative was just a ground, and since it's 1ma it would work. But the diode thing is really blowing my mind. I can't figure that out. Is the circuit testing for resistance? do I need to figure out the resistance at the switch? I have a diagram and the switch does go to ground. And tapping the wire lead I made to simulate the action of the switch works fine. Sorry if this was a long post. I really can't figure this out. My next idea might be to just use a relay. But I would love to know why the diode prevents it from working.

Try using a relay to get a better ground signal and use that to trigger the heated seats.

I went with the relay idea but I didn't have any big relays lying around so I used some micro 5v relays. I stepped down the 12v voltage to 5v and tested everything on a bread board. It all worked great, put it in the car...relays worked fine...aux trigger was working great. Tied them into the momentary heater switch....worked once...both heaters came on. Then nothing, I couldn't even ground trigger the relays. So....I guess micro relays were a bad idea? even if they were rated like 30A and 200V? How could that tiny switch that only has 5v on it and from what I could tell was only using 1ma blow my micro relays? I guess I'll order a bigger relay.

Try using the switches reference wire instead of the chassis ground

pentavolvo wrote: Try using the switches reference wire instead of the chassis ground

I think you were right. I somehow blew my voltage regulator, so I figured the current draw and went with a resistor instead. Everything is working great now. I don't get it, why would going with the ground the switches were using vs another ground make any difference??? Isn't ground, just a ground? did the extra 2 feet of wire add too much resistance or something? I don't know, it's working now though. Should I add like a 1 amp fuse into the circuit incase the relays fry or something?

Are you sure it was 0.94mA and not .94A (940mA)? If it is .94A all of your problems would make sense as your output is limited somewhere between 200mA and 500mA (generally). It would also explain why you burned up your regulator - even if you used a 7805 rated at 1A if you didn't have a heat sink on it it would not survive outputting near 1A for very long. I have had good luck putting a 22 ohm 1/4 watt resistor inline with the coil of 5vdc relays and running them right off of 12vdc with no regulator. It may be worth a shot if you don't have any standard automotive relays to use.Kevin Pierson

I was testing a fluke meter, it said for sure 0.94 ma. But you're putting a seed of doubt in my brain now, so now I have to accept maybe I was wrong, because it does explain everything. I think I might have shorted out the voltage regulator myself, I think I soldered the ground might have touched the 5v terminal. So I'll write that off. I did end up using a resistor like you mentioned, and everything is working perfectly. I have two sort of relate unrelated question for my own person knowledge that I can't figure out. 1. Is ground always "ground", are all "grounds" created equal? Is there ever a scenario where one ground is more special then another? In my mind this only worked because I used the ground the switch was using. 2. If the switch was 5v and it needed a "ground", the chassis ground worked fine. But the 200ma ground on the viper didn't. What is a 200ma ground? the chassis doesn't have a "200ma" ground rating, why does the vipe have a "200ma" rating what does that mean? if I go over 200ma it blows a fuse? or just doesn't work? and if it just doesn't work...how can that be if the seat warmer circuit was 5v and not 12v. I would really love to know these answers, my electronics knowledge is really limited.

In a vehicle "ground" is considered the (-) side of the DC battery (as opposed to an earth ground like with residential AC power). The "chassis ground" is created because the (-) terminal of the battery is physically connected to the metal frame of the vehicle with a conductor. This means that, in most circuits, ground is ground is ground. However, this is not always the case. There are some automotive systems that do supply their own reference ground - these are generally for analog sensors. If you are working with an analog system (and your seat warmers are not) I would verify that there isn't a dedicated analog ground before going with a chassis ground. The cool thing about a (-) output on an alarm/remote start/remote control system is that with a (-) output it does not matter what voltage you are switching. As long as the unit is grounded to the same ground as your voltage source a single (-) output can work with a 3.3vdc, 5vdc, 7.5vdc, 10vdc, 12vdc, 13.8vdc etc system. However, since you are completing a circuit by providing the ground there will be current flowing through your connection. Typically the higher the current rating of an output the bigger the components are and the more of a heat sink they need. Therefore, to safe real estate manufactures often time use low current outputs (transistorized). Many of them used to be 200mA but now most of them are 500mA. It depends on how the manufacturer implemented their output stage as to what will happen if you try to go over the limit. Many older systems would simply burn themselves out and the output would no longer work. It is my belief now that many systems are designed to clamp current output but I have never verified this. These outputs are designed to interface with low current inputs on the vehicle or to drive relays to interface with high current.Kevin Pierson

KPierson, THANKS!!! That answers all my questions. I will accept the fact I probably screwed something up a long the way or did something wrong. Everything you said makes perfect sense now and I have a better understanding of how this all works. Can I trouble you for one more question. Since I added in a circuit, to control the relays, that circuit is using 12v constant and I'm triggering the relays with the negative output from the viper (when car is started of course so I dont drain the battery), works great. Now is this where a fuse comes into play? should I add like a 1 amp fuse in my circuit, before the relays? because if the relays fry it will cause a short in the system if I tried to trigger them? and the fuse would stop this? If my relays use 90 ma, what size fuse would I use? or does it even matter? maybe when a relay breaks it just doesn't work and a fuse isn't needed? is a fuse always needed in any circuit I add?

I have never seen a fuse installed between the output and a relay coil. If the coil were to short (unlikely) you could have an issue but generally when relay coils fail they open. In your circumstance, even if the coil does short you have a resistor inline that will limit the current and offer some protection to the output. If you wanted to add some protection "just to be overly safe" and your load is 90mA I would fuse it around 1.5A. You generally want your load to be 75% of your fuse value. In this case I went a little higher because a 1.5A fuse would be much easier to find and will provide adequate protection.Kevin Pierson