Yet Another Pi Zero Portable!!

moosepr

Hey man

Well I technically have all the bits, just need to iron out a few bits.

My plan with transplanting a 2.8 screen onto a 2.2 board didn't work. The distance from solder connector to screen edge is the same for all screens, so it gave me no benefit. I'm just trying to knock up a little PCB that will allow me to connect the screen with minimal board.

As for the sound, I'm planning on using an adafruit digital audio board https://www.adafruit.com/products/3006 which will give me mono sound for the speaker, or maybe even switchable to the headphones. That would then leave me with a hole where the volume knob should be.

The problem I have now, is once I have got my PCB designed it's going to be another 2 weeks at least. Although I will end up with some spares I could distribute.

thedudester80

@moosepr That I2S amp works great with the pi zero. I used it for my altoid project. Really simple to setup as well.

Tekkaman_Slade

@moosepr - I wish that I2S audio amp was available when I built the NeoPiGamer. I'm definitely going to use it in my next pi zero build. Great find!!! Looking forward to your completed build.

moosepr

yeah that little amp is ideal. Shame its only mono. You can get stereo versions but they are a little larger (although looking at this, it doesnt have much 'amp' in there) https://shop.pimoroni.com/collections/pi-zero/products/phat-dac

The only issue i have, is the I2S board needs pin 18, which is currently what my ili9341 screen uses for its backlight

senkun

@moosepr said in Yet Another Pi Zero Portable!!:

The distance from solder connector to screen edge is the same for all screens, so it gave me no benefit.

alt text

http://www.aliexpress.com/item/2-8-inch-TFT-LCD-screen-display-ILI9341-40-pin-plug-in-type-support-8-16/32627803416.html

How bout this one?

moosepr

@senkun

That would technically work, the board I currently have is only 14 pin. It's the pure SPI interface, where as the 40 pin ones have raw pixel pins bundled.

I'm currently trying to design a board that has a 14 pin ribbon connector on one edge, and 8 pins of SPI on the other. Literally a bare minimum.

You could technically solder wires direct from the screen ribbon to the pi with nothing in the middle, but the 0 8mm pitch ffc connector doesn't lend itself to hand soldering

senkun

@moosepr

I must've been blind not only did not read where it said 40-pin, didn't even see how fine the pitch is. Took one look at the length of the ribbon and thought hey we could drop this on the 2.2" controller board...

btw, are you using the pitft22 dt overlay to enable your screen? Can I have your tft to zer0 pinouts for reference?

moosepr

@senkun

its easy done. there are so many screens and variations of them, its a minefield!!

I used the information from here
http://marcosgildavid.blogspot.co.uk/2014/02/getting-ili9341-spi-screen-working-on.html

then used a little reference image to trace things

https://www.element14.com/community/servlet/JiveServlet/previewBody/73950-102-10-339300/pi3_gpio.png

I was managing to get the thing working with the command

sudo modprobe fbtft_device pitft22 (i think, im working from memory here)

then i could mirror the terminal by typing

con2fbmap 1 1

but i was struggling to get things to activate at boot. Doing a bit of googling, i managed to find a video on youtube that had the solution to my problem. The problem is now, i am unable to find the video :( I will have to ssh onto my zero and use the command history and see how i fixed it

moosepr

so now i may also be able to add PCB design to my skillset

https://oshpark.com/shared_projects/BP9tGKag

in theory you can solder a 2.2" ili9341 screen direct to that board, then add wires from there to the pi

the 2.4" and 2.8" screens have an extra 4 pins on the connector, but thats just for the touch, so they could just be snipped off the ribbon (hopefully)

The resister on there is just for the backlight, you can change it to alter the backlight brightness, and it means there is one less pin needed from the pi (so i can use pin#18 for audio)

its the first PCB i have designed, so it may not be perfect, and it is untested, so it could burst int flames, who knows!!

senkun

@moosepr said in Yet Another Pi Zero Portable!!:

sudo modprobe fbtft_device pitft22

Ah thanks. That's already in the latest kernels, so it can be enabled by adding to config.txt;
dtparam=spi=on
dtoverlay=pitft22

in theory you can solder a 2.2" ili9341 screen direct to that board, then add wires from there to the pi

Haha. Nice little board. But wait! We can ditch the original red pcb and just solder screen ribbon wired direct to the zer0's gpios?

Here is the 2.2" tft without touch screen, just the 9 pins but there's that cap and resistor plus u1, q1, j1 which is not needed?

edit: seems like u1 is a 65z5 +voltage regulator chip which doesn't seem to be present on the 14 pin touch versions.

alt text

moosepr

@senkun yeah my board might be a little too minimal, but it's only costing me $2.20 for 3, so it's worth a punt. The only down side is the wait.

If it does work, I'm planning on making a custom board that will will link it all together into one. 2.2 screen on the front, some buttons on the button in a DMG-01 layout.

senkun

@moosepr said in Yet Another Pi Zero Portable!!:

@senkun yeah my board might be a little too minimal, but it's only costing me $2.20 for 3, so it's worth a punt. The only down side is the wait.

If it does work, I'm planning on making a custom board that will will link it all together into one. 2.2 screen on the front, some buttons on the button in a DMG-01 layout.

Apparently these screens will not work unless they're getting a strict 3.3V hence that 65Z5 regulator on board.

I'd say you need to regulate power to it somehow. Take it from the Zer0's 3.3V? You've ordered the boards so it'd be interesting to see if and how well it tolerates fluctuating power directly off a Lipo (from 4.2V max ~ 3V safe cutoff).

While the Zer0 can and has been tested to boot from as low as 2.8V (very unsafe if Lipo) and run unless there are 5v usb peripherals. But you have that charger/protector module (I think that cuts at 3.2V) and you've tested it running from just the Lipo with memory sticks and wi-fi dongle. So everything should still work if the screen is tolerant.

moosepr

@senkun
I am running my screen from the 3.3v line on my zero anyway, so I'm assuming everything will be OK without regulation.

Your brave ordering my boards! I couldn't find a proper connector in fritzing so i had to hand build one from the normal pads. There are some things quite close together, so it will need to be tested for shorts.

senkun

@moosepr

hey how's it going?

So I finally got hold of them Ilitek screens, one of each size! Been playing around with them, I couldn't find an existing overlay that I could just pop in (thought pitft22 would work but nope). So yeah, probably gonna compile my own dt blob, but went back to fbtft and modprobe to mess around first. Still using gpio 18 for led but gonna reassign and use that for pwm audio out.

The screens are pretty zippy. with buffer throughput set to 32k, stable at 48000kHz and probably getting more than 30fps, no flicker, some slight tears only when large blocks are dumped quickly. But the viewing angles in horizontal orientation are terrible! Really bad unless looking straight on. They're all originally used for low end cellphones and designed for vertical viewing, but still good bang for the buck I guess.

All three of my screens seem pretty dark though, how's the backlight levels on yours? Did you play around with different resistors for the leds?

moosepr

@senkun

Hey man, I'm still watching the door, waiting for a tiny parcel filled with PCB's. I did get a notification the other day that it had been despatched, so it can't be much longer now.

I have noticed the tearing in fast and full screen changes, but there is nothing major. I have only used gpio 18 for the backlight, that seems to use a transistor and a few little resistors, so is pretty much 3.3v going in there. The screens don't have brilliant viewing angles yeah, but I guess you get what you pay for eh? The best in my option is oled. Viewing angles are always amazing because of the way they work, but they are hard to find and expensive.

senkun

@moosepr

Haha if it's from OSH all the tiny pcbs are gonna be floating loose in an envelope. I was thinking of soldering directly to the ribbon but I see now why you did the pcbs.

alt text

moosepr

@senkun yeah i think hand soldering cables to 0.8mm pitch flex cables is a bit of a push :P

pikgoggle

How did you use the microcontroller as a power switch?
Did you use a mosfet?
Can you please share the code?

Also, I noticed you didn't use a power boost module or a regulator, can the screen run directly from the battery voltage which is under 5V?

Thank you

moosepr

@pikgoggle i used a little board from DFRobot called uHex http://www.dfrobot.com/index.php?route=product/product&product_id=1266

it is basically an arduino, with a little MOSFET built in, and you can use its library to make it sleep/wake and when it is asleep, the 6 power ports are off. The code is a little basic at the moment, and is not without its flaws. the wake interrupt fires instantly, and the pi starts to boot before the code has chance to check for a long press. Also as soon as the board gets power, the pi will also start to boot, so if the battery protection kicks in, its hard to get it all to actually charge (gets stuck in a loop of charge/protect) I also planned on adding a neopixel in there, so i could get power metering, and adding connection to the pi to check for the pi being on/ and offering safe shut down. I did start adding that into the code, but never got to finishing it. You can have a butchers at it here https://drive.google.com/file/d/0B8-rbOfCiqw0MkRiYnFqbU1MWk0/view?usp=sharing

@senkun the post man came today!! Although i have some family moving in with me soon, so im not sure when i will have the time :(

Yay

pikgoggle

@moosepr if you just want a power switch, if your mechanical switch can't handle the current, you can use this circuit:
http://www.falstad.com/circuit/circuitjs.html?cct=$+1+0.000005+10.20027730826997+50+5+43 s+160+112+224+112+0+1+false r+384+112+384+256+0+10000000 g+384+256+384+288+0 v+160+240+160+112+0+0+40+5+0+0+0.5 g+160+240+160+304+0 w+464+128+464+208+0 w+160+112+160+32+0 w+160+32+464+32+0 w+464+32+464+96+0 w+464+208+464+272+0 r+464+272+464+336+0+100 g+464+336+464+384+0 w+384+112+224+112+0 f+384+112+464+112+1+1.5+0.02 o+10+64+0+35+5+0.05+0+-1

the PMOS transistor is used to drive the high current, while the mechanical switch only activates the gate with a low current.
The 100ohm resistance represents the load.
It can be done with NMOS too.