Alternative power switch?

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Posts: 1
Joined: Wed Oct 04, 2017 3:28 am

Wed Oct 04, 2017 3:39 am

I am using the LP for a car PC/ head unit... i have it figured out to where the LP powers on when i turn the key, i am looking for a way to maybe power the Lp down safely once i turn the key back off maybe using Arduino or the remote wire. Is there a way to wire a button via Arduino or sensor connectors?

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Posts: 65
Joined: Mon Oct 24, 2016 10:38 pm
Location: USA

Wed Oct 04, 2017 11:46 am

This is not an easy to fix problem. Since you need it to remain powered for a short time after the car is off.
I can give you a solution if you aren't using Auto-On, with the panda, but you'll still need to use a power button to start it up. But it'll turn off automatically. But if you have it set to turn on automatically when powered, then this solution won't work for you.

Using a couple Li-Ion cells in parallel, with a 3.7v to 5v charge/boost board. (not li-poly), make/buy a UPS for the panda. Really it only needs to keep it on for a couple minutes.
Program the arduino so it reads 5v through an analog pin from your 12v->5v adapter, on the 5v side.

Ok here's how it works. The UPS will keep the panda on for a minute or so when the car shuts down. The arduino will sense that the power to the UPS Charge board was cut, and the arduino is programmed to work as a keyboard HID. That will then send a shutdown command to windows (like the shutdown key on a pc keyboard). Which will cause the panda to shut down.
The battery should be enough to keep it going in case of a long shutdown.

The only auto-on solution i can think of, is using a mechanical relay that is powered by both the arduino AND the 5v power source. And programming the arduino to check for a system response from windows, and if it doesn't receive anything for 2-3 minutes, to cut the relay (setting the pin low). (A suicide relay)
Where as if the car is on, the relay will be enabled by the car's 5v source for the panda/charge board. So i'll get power from the car and/OR the arduino.

I've used suicide relays in projects before. The way i'd do it, is i'd press a power button to a microcontroller, wait until the microcontroller passes it's boot loader and enables the relay, bypassing the power button. (i just hold the power until it clicks) and then when the microcontroller is ready to suicide, it just brings the relay low and it cuts the power.

Here's a relay module. the IN goes to a gpio, and then the VCC goes to the panda's 5v, like from one of the CN2 connectors.

Don't want to run a relay coil right from the gpio, they draw too much current so a transistor driver, like in those modules, is the way to go.
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Posts: 15
Joined: Tue Mar 13, 2018 1:47 pm
Location: Maine USA

Wed Feb 05, 2020 12:45 pm

Check out using a DCDC NUC car PC power supply. It is "smart" and can control start up delay and shut down. We have it set to send power to the auto start Delta 10 secs after car Ignition hot and shut down (by USB signal) the Delta some time after car turn off.

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