This is a Power Management utlity which is primarily built for the Gameboy Zero project. This adds graceful shutdowns from the main power switch and automatic low battery alerts and shutdowns when the battery level is low. This is meant to be used in concert with the provided list of required hardware and components within a Retropie 3.7+ environment.
This solution will work in any portable battery powered raspberry PI unit that uses a Powerboost 1000C. So not only can this be applied to the Gameboy Zero project, but also to the Adafruit Pi Grrl and Pi Grrl 2 projects as well as a wide variety of portable retro gaming systems or IoT solutions that use the Raspberry Pi and a Powerboost 1000C
Currently in the GBZ, the power switch works like a normal On/Off switch. The only problem is when you cut the power, it's kinda hard on the system. There's no clean dismounting of the drives. It's really just like yanking the power out. And that's been known to cause corrupted files and disks.
My goal is to add an inexpensive and small electronic switch that will take care of the killing the power part, but only after a clean shutdown process. After some research, both the Pololu Mini Pushbutton LV or the Pololu Mini Slider LV will both work and fits our needs. They are basically identical in size and price ($5) with a couple extra features on the pushbutton version.
The main power switch will toggle ON the Pololu switch (but only ON, not off). Then, we need 3 GPIO pins mapped, one as output, and two as input. Once the unit is turned on, we use the built-in UART TX pin and send a signal to the ON pin of the electric switch which overrides it to remain on. (Alternatively, for the Pololu Mini Push Button switch, we use a GPIO pin mapped with the GPIO-Poweroff driver which maps to the OFF pin which tells the switch to shut off when we successfully power off). This ensures the system remains on until we are ready to shut it off. Another GPIO input pin will read the setting of the power switch, so we can tell when the user wants to shutdown. And lastly, the final GPIO input pin will go to the pin attached to the Low Battery LED of the Powerboost, so we can gracefully power down automatically when the battery is very low. A nice little add.
- Raspberry Pi Zero (or Model B+, Raspberry Pi 2 and Pi 3)
- Adafruit Powerboost 1000C
- Pololu Mini Slide Switch LV or Pololu Mini Push Button LV
- 2N3904 NPN transistor
- 47k resistor
- A mini SPDT or DPDT latching push and hold switch (for emergency resets and prolonged storage)
- Original DMG (or equivalant) SPDT Slide Power Switch
- Retropie 3.7+ or latest Raspbian
- Python 2.7 and Python Module RPi.GPIO (comes installed with Retropie 3.7)
- omxplayer (comes installed with Retropie 3.7)
- Must be run as a sudoer user (the default Pi user on Retropie 3.7 is a sudoer)
- The built-in slide switch on the Pololu switch in the diagram must be flipped into the off position to work
- If using the alternate Pololu Mini Push Button LV, instead of using UART TX to the ON pin, map physical pin 7/GPIO4 to the OFF pin of the Pololu Push Button LV and add the following to the /boot/config.txt file
dtoverlay=gpio-poweroff,gpiopin=4
- the 2nd VOUT & GND from the Pololu switch (labeled Video DC) can go to the power strip from Wermy's video guide 4
- In Wermy's latest wiring video guide number 4, he wires the main power switch to be closed when OFF, this needs to be inverted for the Pololu switch. Use the other pin on the switch which closes when ON (or just turn the switch around). These will be mapped to the SW and GND pins of the Pololu instead. (or to A and B of the Pololu Push Button version)
- If the latching emergency reset doesn't work, try mapping it to a shared ground.
You will need to connect the PI Zero to Wifi and from another computer on the same WiFI network, SSH in (or use Putty on PCs):
ssh pi@retropie.local
Default password is 'raspberry'. Next at the command prompt, copy this monitor and the video assets with the following command:
cd ~;git clone https://github.com/thinkflo/GBZ-Power-Monitor.git
Now, launch the Monitor manually and test that it's working properly
python ~/GBZ-Power-Monitor/gbz_power_monitor.py
Once you are satified that the monitor behaves properly, add the monitor to the startup process to complete the installation and then reboot to make it live.
echo "@reboot /usr/bin/nice -n 19 /usr/bin/python ~/GBZ-Power-Monitor/gbz_power_monitor.py" >> mycron; crontab mycron;rm mycron
I'm always tinkering with the script to fix bugs and improve it's stablity. There's a bunch of changes I'm planning to add including the ability to detect when the power is plugged back in, which would cancel the shutdown process. Presently, once the shutdown process is activated, it will shutdown even if you had rushed to go plug in the unit. I also want to add logging and implement proper threaded processes. Right now, it's a bit uglier than I would want.
So, as I continue to tinker and add these things, you can make sure you have the latest updates by issuing this command
cd ~/GBZ-Power-Monitor;git pull origin master
What is the purpose of the Latching Switch? Since we are changing the way the PI powers down, by software, in case your Pi has a kernel panic or, for example, the monitor unexpectedly crashes, your pi will be stuck on and you'd have to get your screwdriver out to reset it. How annoying! So this was added as a way to do that. It's also used when you want to store the unit for longer periods of time, this lets you disconnect the batteries. The button should be recessed so it's not easily hit. ie: Mount it internally and drilling a pin hole where a paperclip is needed to hit it.
Do I have to use the Powerboost 1000C and not another type? Maybe. You could use other power supplies, however, if they do not have a Low Battery indictor like an LED or dedicated pinout, then you will lose the automatic Low Battery warnings and shutdowns, which one of the core functions of this monitor. But even so, you could still use this for the dedicated power switch which would still gracefully shut down. You might have to reconfigure your emergency latching switch though. Let us know about your success or failure stories!
https://www.youtube.com/watch?v=TRkEfD04unk Low Battery Warning
https://www.youtube.com/watch?v=nRJ42oSrIg4 Power Switch test
More detail can be found on this thread:
http://sudomod.com/forum/viewtopic.php?f=8&t=97
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