How to make negative pulse output from a dry contact

Thread Starter

xtacie

Joined Apr 27, 2022
2
Howdy everyone. Im soo glad I found this place, looks like Ill be around a lot longer with all the interesting stuff Ive come across here, deffinetly bookmarking this place... anywho...

I have a battery monitor to monitor the voltage level of a 2nd battery bank. I have installed a Viper DS4 alarm/remote start and the unit has an activation input that is looking for a "negative pulsed" input to remote start the vehicle for 40 minutes so the battery's charge and then the vehicle shuts off (is what im trying to accomplish). I have two different battery monitors but their outputs are dry contacts. How can I create or can I purchase something like a relay that would sense the dry contact input and throw a negative pulse output to activate the remote start.
 

AnalogKid

Joined Aug 1, 2013
10,050
Please post a sketch of the various components and interconnections. Be sure to give each component a unique reference designator for discussion.

By "negative pulse", do you mean a negative-going pulse, such as a signal that sits at 12 V and pulses down to GND, or a true negative pulse, one that sits at GND and pulses down to some negative voltage? Both are doable with a resistor and a capacitor, but the connections are different.

What is the impedance the pulse is driving? IOW what current must the pulse supply to its load?

ak
 

Thread Starter

xtacie

Joined Apr 27, 2022
2
FIRSTLY, thank you for you response. I just got off the phone with viper and the activation input on their unit is only looking for a ground. He said if i put a wire on the input and tapped the chassis or any ground point it will trigger the remote start. I believe its a momentary ground, not a constant. I dont have the ability to draw a diagram as I am on the road at the moment. But it is very simple setup. The output of the battery monitor is 2 wires and they can be programmed to be NO or NC. The activation input wire on the starter is a single wire looking for a ground momentarily. Hope this helps
 

AnalogKid

Joined Aug 1, 2013
10,050
Sounds like the input has an internal pull-up impedance of some kind. If we are lucky, you can drive this through a capacitor so it forms a differentiator that converts the level change into a pulse. To calculate the correct capacitor size, we need to know two things:

1. The minimum (and max. it there is one) input pulse width, the amount of time the input is pulled to GND.

2. The input pull-up impedance.

3. This one is wishful thinking - the actual input transition level. This is the voltage at which the input stage decides that action is desired. for a 12 V system, this might be around 6 V, but I've seen some systems where it is very low, like 1 V above GND.

If you tell them what you are trying to do, they should have no problem giving you these details.

There are several DS4 userr manuals on the Viper site. Which one is yours? Also, links to the battery monitor.

Gold Star for contacting the manufacturer directly.

ak
 

sghioto

Joined Dec 31, 2017
3,270
Setting the release time for appx 1 second will work using this module.
1651086122545.png
DC 12V Adjustable Times Switch Module Signal Trigger Turn Off Timer Delay Switch Module 0~25Seconds Time Delay
 
Last edited:
Top