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- ellindseyParticipant07/12/2015 at 02:17Post count: 7ellindseyParticipant06/22/2015 at 16:10Post count: 7
Here’s how I have the power control circuit set up.
[attachment file=”power wiring.jpg”]
I’m using a Powerboost Charger 500 circuit from Adafruit, which made the power control circuit fairly easy to build. I did have to desolder the pull-up resistor on the powerboost enable line to prevent it from turning on all the time. This circuit uses GPIO14 (the UART TX line on the Pi) as part of the latch circuit. Pressing the power button momentarily brings the enable line high, then the output from pin GPIO causes the latch to stay on. When I shut down the Pi through the Emulationstation menu, GPIO14 is brought low when shutdown is complete, which discharges the 10uF capacitor and pulls the enable line to shut power off. You can also manually turn it off by holding the power button down for about 3 seconds.
I don’t have any feedback from the power button to the Pi to trigger software shutdown when the button is pressed, although that wouldn’t be hard to add if I wanted it. Shutting down through the menu seems to work fine for me, and the current setup doesn’t require any software modification to work.ellindseyParticipant06/16/2015 at 04:31Post count: 7
Working on the soft power switch. I’m working on a latch circuit which uses the GPIO14 output of the Pi to indirectly drive the Enable line on the Powerboost circuit. Tapping the red button turns it on, holding the red button for 5 seconds forces it off. The first attempt didn’t work as I didn’t realize that when GPIO14 goes low on shutdown it’s not a hard low but a soft pull-down and it’s not strong enough to turn the latch off. Going to make some changes to the schematic to get that to work.ellindseyParticipant06/15/2015 at 14:33Post count: 7
Not completely sure as I haven’t yet done a full test of running it with a completely full battery down to shutoff, but it looks like about 2 hours of run time. I can run it with the charge cord plugged in which extends the run time, but it still discharges faster than it charges so I can’t run it indefinitely.ellindseyParticipant06/13/2015 at 17:43Post count: 7
The screen is part B005CFLMNC from amazon or from many other online resellers. It’s a 4.3″ TFT LCD meant for car backup cameras. I removed the rear case and mounting hardware, but kept the front case and incorporated it into my design rather than burying it inside the case like most people do.
Surprisingly this screen runs fine off 5V, despite it claiming it needs 12V and most of these needing at least 6V to work properly.