Pi in a PSP

[othermod]

@othermod I originally borrowed the UART pin idea from @Popcorn but we decided using a BCM pin was stable in half the time during boot up.
The schematic I've designed to go with the banggood supply is essentially the same as your dual MOSFET setup.

@Camble How does that pin (I think it's 22 from reading your posts) act during a reboot? Using the TXD pin, if I restart the Pi, the pin goes low and kills power to everything. I then have to power it back on. I was going to remedy this by adding a capacitor to the gate to keep the mosfet enabled for an extra second or two, but if your pin stays high then it would be a better solution.

[Camble]

@othermod Good question. I'll have to check.

Also, you need to add the following line into /boot/config.txt

Code: Select all

dtoverlay=gpio-poweroff,gpiopin=22,active_low="y"

[othermod]

@othermod Good question. I'll have to check.

Also, you need to add the following line into /boot/config.txt

Code: Select all

dtoverlay=gpio-poweroff,gpiopin=22,active_low="y"

@Camble Okay I've been reading through the posts, trying to wrap my head around everything. Does the config code only make the GPIO pin go low after shutdown? Also, as I understood it, the GPIO is in an unstable floating state during bootup, and that's why I used the TX (and because it saved a GPIO pin for something else). Am I wrong about that?

Also, I'm looking at the gbz_power_monitor.py file that @popcorn posted and it appears that he solved another problem I had. I've made a very simple low-battery warning circuit using an LM393 dual comparator. What is does is compare a reference voltage (like the 3.3v from the Pi) to the battery voltage. If the battery voltage drops below the reference voltage, it switches an output high or low depending on your preference. Right now this output supplies the GND to a low-battery LED. I intended for the other output from the LM393 to connect to the same pin that detects a falling edge and issue a shutdown, but I know that if the battery is low when the OS is booted then the GPIO pin will stay low and there will be no falling edge to detect. I assume he resolved this with this code:

Code: Select all

81 def main(): 
82   #if the Low Battery LED is active when the program launches, handle it  
83   if GPIO.input(batteryGPIO) is 0: 
84     lowBattery(batteryGPIO) 
85 
 
86   #if the Power Switch is active when the program launches, handle it 
87   if GPIO.input(powerGPIO) is 0: 
88     powerSwitch(powerGPIO) 

What I don't like is that it appears that multiple GPIO pins are used for this setup. One to sense the powered-on state of the Pi, one for the Pi to sense the low battery, and one to shut the OS down. I think it's possible (with the dual mosfet design at least) to combine the power sensing and the shutdown into one GPIO pin.

Everything I'm designing is based around using the banggood power supply, since the powerboost isn't cheap. That's why I made the LM393 circuit.

I'm very excited by what I'm seeing on this site. You guys have solved many of the problems I've been working on. I hope to be able to return the favor.

[Camble]

@othermod The LM393 is exactly what I've used.

[Camble]

@Camble Okay I've been reading through the posts, trying to wrap my head around everything. Does the config code only make the GPIO pin go low after shutdown? Also, as I understood it, the GPIO is in an unstable floating state during bootup, and that's why I used the TX (and because it saved a GPIO pin for something else). Am I wrong about that?

I think you're correct, but the UART TX pin seemed to stabilize at 3.3v after 8-10 seconds, whereas a BCM pin with the gpio-poweroff flag set will stabilize after 5 seconds. Again, I'm not sure about reboots.

This may be helpful

http://sudomod.com/forum/viewtopic.php? ... 330#p10970

[othermod]

I think you're correct, but the UART TX pin seemed to stabilize at 3.3v after 8-10 seconds, whereas a BCM pin with the gpio-poweroff flag set will stabilize after 5 seconds. Again, I'm not sure about reboots.

This may be helpful

http://sudomod.com/forum/viewtopic.php? ... 330#p10970

That's strange. I get a stable power-on in under 2 seconds with the TX pin. The small delay is a great feature in my project because it prevents an accidental power-on. Also, if an SD card is not installed, the TX will not pull high and the system will not stay on (another thing I consider a feature). I will have to test to see whether a GPIO pin has the same function. I'm doing more reading about the pins you guys are using. At a minimum, it would be nice to use one pin for both portions of this. Right now I use the TX for pulling the P-mofset up and a regular GPIO pin to detect the power button being pressed and issue a shutdown. Using your method I can possibly avoid using the TX and leave it open for other things.

Here is what I'm thinking:

The GPIO pin will be pulled high at bootup and keep the N-mosfet enabled. When the OS is running and the power button is pressed, the GPIO will be pulled down and the shutdown will begin. At this moment, the GPIO will be low and the P-mosfet will be disabled, but the power button should keep the P-mosfet enabled and keep the system powered on. My only question is what will happen when the power button is released. When the button is released, there will no longer be a ground connection keeping the P-mosfet enabled, and I am unsure whether the N-mosfet will come back up quickly enough to supply the GND for the P-mosfet gate. A small capacitor on the P-mosfet gate would probably remedy any issues.

[Camble]

I'm sure TX will do the trick for dual MOSFET, but a fluctuating gate voltage wasn't enough to keep the the JFET off in my safe shutdown circuit.

[othermod]

Okay so I built the circuit in EveryCircuit. Instead of the TX pin and a GPIO pin, one GPIO pin is used both for pulling the n MOSFET high and for issuing the shutdown command. The only thing it's missing is an emergency shutdown after a long button press.

http://everycircuit.com/circuit/4575239031226368

[johnweland]

ugh, I'm stoked to see this. especially after watching wermy do his new video building a gbzero with all customer parts no GB actually being used. I've got a psp shell in my amazon cart ready to buy when we have boards ready to go!

[othermod]

ugh, I'm stoked to see this. especially after watching wermy do his new video building a gbzero with all customer parts no GB actually being used. I've got a psp shell in my amazon cart ready to buy when we have boards ready to go!

I'm continuing to work on it, getting closer every day. I got a little distracted because a magazine in the UK is doing a page on the PSPi project and that's had my focus for a couple days. I'll be posting an update soon.