Automotive Memory Saver with added functions(Circuit dilemma)

Thread Starter

NewV+

Joined Mar 18, 2021
1
Hello Everyone( New Member),

I’m building an automotive memory saver that uses a 9V battery, has a V meter and and an LED to indicate battery power ON. I currently have the Volt meter display Battery Voltage with the push of a switch(SWT 2). When you push SWT 1 an LED turns on and B+ is sent to PIN 14 of the Automotive DLC connector and supplies power to Vehicle ECM while battery is swapped out, with out loosing memory. I also want the volt meter to display vehicle B+ just by plugin in memory saver, as DLC connector PIN 16 is constant B+. But the only way I’ve thought of so far as to accomplish this is by running parallel to B+ coming from DLC pin 16 to the V meter. That works great and all. Vehicle B+ is displayed on the volt meter,(this is we’re I’m having the issue!!!) but the Volt meter will also turn on when SWT 1 is pressed, and that is something I don’t want. I want to be able to have the Voltmeter display Device Voltage, Vehicle B+ and not turn on when Switch 1 is pressed. I thought of adding another switch to Volt Meter B+ coming from vehicle, so it won’t turn on when switch is pressed. But that would be 3 switches for a very small enclosure. My mind is just exhausted as it’s currently 1 am in the morning and can’t think straight. I would definitely love to hear your smart people’s thoughts on this and any suggestions to help improve this circuit.
Looking forward to learning a bunch from this forum !!!
(Please excuse the hand drawn circuit)

Thank you
 

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Yaakov

Joined Jan 27, 2019
3,517
Hello Everyone( New Member),

I’m building an automotive memory saver that uses a 9V battery, has a V meter and and an LED to indicate battery power ON. I currently have the Volt meter display Battery Voltage with the push of a switch(SWT 2). When you push SWT 1 an LED turns on and B+ is sent to PIN 14 of the Automotive DLC connector and supplies power to Vehicle ECM while battery is swapped out, with out loosing memory. I also want the volt meter to display vehicle B+ just by plugin in memory saver, as DLC connector PIN 16 is constant B+. But the only way I’ve thought of so far as to accomplish this is by running parallel to B+ coming from DLC pin 16 to the V meter. That works great and all. Vehicle B+ is displayed on the volt meter,(this is we’re I’m having the issue!!!) but the Volt meter will also turn on when SWT 1 is pressed, and that is something I don’t want. I want to be able to have the Voltmeter display Device Voltage, Vehicle B+ and not turn on when Switch 1 is pressed. I thought of adding another switch to Volt Meter B+ coming from vehicle, so it won’t turn on when switch is pressed. But that would be 3 switches for a very small enclosure. My mind is just exhausted as it’s currently 1 am in the morning and can’t think straight. I would definitely love to hear your smart people’s thoughts on this and any suggestions to help improve this circuit.
Looking forward to learning a bunch from this forum !!!
(Please excuse the hand drawn circuit)

Thank you
I am not entirely sure I follow your requirements but it seems that a DPDT center off switch will do what you want. In one direction it would connect the battery and disconnect the meter, in the other it would do the opposite, in the center nothing would be connected.
 

Tonyr1084

Joined Sep 24, 2015
6,269
In my truck and my wife's car, there is a fuse panel inside the hood (bonnet as some call it). Inside the panel there's a connection from the battery. Whenever I change a battery in a vehicle I connect an outside source 12V to the positive terminal in the panel and ground the negative terminal. Then when I remove the battery cables from the car or truck I just make sure the positive battery cable does not contact ground. Swap the battery and disconnect the secondary (outside source 12V). No need to mess with memory pins or clocks or whatever else requires power. Just be sure your outside source is able to supply sufficient current during the swap.

I use a "Werker Batteries WKA12-5.1A" battery when changing car batteries. 5.1 amp hours is big enough to keep memory while changing things. You don't have to reset the ECU, clock or your radio stations. 5.1 amps is not strong enough to start any fires. Just don't hook it up backwards. Attention to detail is key.

Oh, and welcome to AAC.
 

Yaakov

Joined Jan 27, 2019
3,517
In my truck and my wife's car, there is a fuse panel inside the hood (bonnet as some call it). Inside the panel there's a connection from the battery. Whenever I change a battery in a vehicle I connect an outside source 12V to the positive terminal in the panel and ground the negative terminal.
There are some devices that plug into the cigarette lighter with a 9V battery like this:

https://www.amazon.com/Connector-Battery-Memory-Keeper-Saver/dp/B07KCN69LJ

This one also has an OBD version.
 

shortbus

Joined Sep 30, 2009
8,817
I for one don't understand the reason for doing this, other than if you have power seats that remember what driver is behind the wheel. Radio station settings? Kind of lame if that is the reason. All other things reset to factory memory, engine, transmission what ever. Most cars self learn your bad habits in driving, a reset from time to time will usually get you both better performance and better gas mileage, until the computer relearns how you drive. The original settings are an "average" of many peoples driving and vehicle testing, usually much better than the owners driving settings.
 

Tonyr1084

Joined Sep 24, 2015
6,269
Well, you can do the same thing with a 12V battery and the cigarette lighter.
Some cigarette lighters (a.k.a power ports) are not active unless the key is on. Some cars the computer turns everything on; so if the key is not on the power ports are off. My cars don't have keys, they're PTS (push to start/stop).

My friends Dodge Demon (70's model), you could turn the four way flashers on and the radio would play - stop - play - stop - play - stop - play - stop (etc.)
 
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