Another portable Pi Project!


#1

HI everyone. Firstly, apologies. I am sure this has been asked a million times before and I have done a few searches and learned from them, i do however have my own problem I am hoping someone can guide me on.

Brief description of project. I am building a portable Pi to run Retropi on. I have designed and made a 3D printed case, I have a Pi 3B+, a 7" HDMI screen from Amazon, a powerboost 1000c, an onoffshim, a 6600mAh battery and various other bits to piece it all together.

Now, the problem I have is simply that upon piecing everything together, I am getting under voltage. I briefly read somewhere on the webs that the Pi3B+ might NOT work in this configuration. My electronics knowledge is limited, so I havent measured the various outputs/inputs of power, but i had figured (probably wrongly) that the 6600 mAh 3.7V battery plus the Powerboost 1000c would have been enough to power the Pi and the 7" screen plus bluetooth etc…

When I mocked up a design but used a standard powerbank it was all ok (using both USB outputs) but the total output from that power bank wasnt anything over 4amp i dont think, so I am a little confused and i feel ive done something wrong!

Am I right in thinking that the B+ wont work in this configuration? My portable handheld Pi is limited space wise, so I was trying to keep the battery as small as possible hence purchasing the powerboost/battery/onoffshim which all fit lovely…

hope you guys can help!

thanks


#2

IMHO It’s much more likely its an undercurrent problem. The Powerboost 1000c can only supply 1A out. Hit that limit and it probably reduces the voltage out as a means of limiting the current draw.
A https://shop.pimoroni.com/products/mp2636-power-booster-charger-module may be what you need. 2.5A out.


#3

thank you Alphanumeric, I really appreciate your input. I guess I have completely misunderstood the Powerboost 1000c capabilities, for some reason I though it was outputting a lot more than 1000mAh, i thought that was the charging current, ah well, im learning at least! Thanks for the link, ive had a read up and yes it looks like that might work I just need to check that it will give me enough power for the Pi3B+ and the screen etc…

thanks again


#4

I have several Powerboost 1000c’s here. They are powering Pi Zero’s and A+'s. I have an MP2636 on the way to play with. I won’t have it for a week or so though. Only just ordered it the other day and used the snail mail option. ;)
No enable pin on the MP2636 is an issue for me. I use that on almost every setup with the Powerboost 1000c. It lets me turn the upconverter off so the Pi is off, only the battery recharger is on. I want that mode on my rovers.
My plan is to figure out which pull up resistor is wired to that pin and solder on a wire so I can pull it low with a switch. I have the schematic with chip pinout.


#5

The official Pi power supply is rated for 2.5A. And thats what Pimoroni recommend for the new Picade. So, 2.5A should be enough? As always YMMV, all depends on what current your display wants. As far as the PI goes look here. ops, glitch on that page. Normally if you go here, https://www.raspberrypi.org/ Then go to the bottom of the page and click the FAQ link, you will find a power section with the power requirements or the various Pi models. I’m getting an error today. =(


#6

i will have a read. I do need to check the power requirements of the 7" screen, it may be pulling just a little too much I dunno. Looking through various other post on the webs, I noticed a lot of people are using the Pb1000c, but they all use different screens to mine, plus the official Pi 7" screen seems common and seems to work in my setup so I do wonder if i need to compare both screens power requirements…ill do that…!


#7

right - my screen requires 1000mAh, the official Pi 7" requires around 470mAh… :/


#8

All my Powerboost setups are headless, no keyboard, mouse or display. And when I do connect a display its self powered. Your typical PC HDMI display or a TV. Thats likely why I haven’t run into issues so far. I bought the MP2636 because on one setup, I want to swap out a Sense Hat for a Unicorn Hat HD. That 1A limit may become an issue on that build. I also have an LED Shim hooked up. Long term, I also want to replace the Pi A+ with the rumored 3A+. If that happens the Powerboost 1000c for sure won’t be enough to drive it all.


#9

I have one of the original Pi Foundation screens, resolution isn’t anything to get excited about, IMHO.


#10

yeah, certainly looks like i am probably just over the limits of the power i can provide the devices. I may have to revert back to my original plan of using a butchered power bank, which is annoying because of the size of the batteries and flimsiness of the metal connectors to the batteries - very easy to break.

I chose the screen I have because it really is great, much nicer than the Pi 7", though obviously it requires that much more power…


#11

Another option is a second powerboost and battery. One powering the PI, and one powering the screen.
EDIT: use two smaller batteries, maybe get the biggest MAH flat ones you can instead of the round ones.


#12

They fixed the broken link, https://www.raspberrypi.org/help/faqs/#topPower


#13

I was hoping Adafruit would do a Powerboost 2500c, based on the chip used on the MP2535. With all those extra pins like the enable pin.
That “one” mounting hole on the MP2535 kind of bugs me too, what’s up with that?


#14

Here are my Pi project pictures, if you want to have a look see, https://1drv.ms/f/s!AjOYwiwlwDtpgUMsp2qnevKpGEHb
One of the few things OneDrive is good for. : P


#15

some cool stuff on there!! I dont have anything super interesting as yet, just various Retro gaming devices. I always wanted to build my own hand held so thats my main focus and has been for a long while now…


#16

I started with some very basic stuff. Then as time went on I got more adventurous. My background is in electronics, I’m a retired electronic technician. I also did some circuit board fabrication etc early on in my carrier. It’s coming in handy now.
A Dremel tool with various cutting and sanding attachments comes in really handy. A good quality soldering iron is a must to IMHO.


#17

It’s very interesting stuff. Pretty much why I’ve started this project. Just looking back and good point about doubling up on the power - I might have a think about that to see if it’s viable. I would still want to power on and off via one button however, so I’m not too sure if I can piggy back…going to think about this one!


#18

What I did on one of my projects is code a shutdown via a button press. The button is wired to a GPIO pin and it does a Raspbian shutdown via python code added to the python file it runs on bootup. Once the Pi shuts down I flick a power switch to turn off the powerboost via the enable pin.
I do it on a couple of my Pi setups. Some I just leave powered, then when I want to start them I momentarily short the RUN terminals on the Pi. Same type of pushbutton I use for shutdown. Normally open momentary contact.
I think the one power source is a better option for your project. Was just throwing options out there is all. ;)


#19

great ideas! I currently have a shut down script programmed in for the onofffshim - nothing ive made myself, just available stuff, that works well but as you say the actual powerboost stays powered on - which I guess is a requirement of the onoffshim although your idea of a “secondary” switch might be an idea…that said, if im having power switches everywhere i could easily solve my power problem by adding a second battery for the screen and having two switches plus the power button arrgghhh :)


#20

Grounding the enable EN contact on the Powerboost 1000c will turn it, and anything powered by it, off. The Blue LED will turn off and the upconverter, the part that boosts the battery to 5V, will turn off. With the 5V out off, your Pi and or screen will be off. The battery charger part will still be on so you can recharge your battery. It’s a lot easier on the power supply feeding it this way. Its only recharging the battery.
You can get double pole single throw switches. Its basically two switches in the one housing with only the one handle. Moving the handle switches both switches at the same time.
So you wire one powerboost to one pole (set of terminals) and the other powerboost to the other pole. It’s two sets of NC, C, NO. Normally Closed, Common, Normally Open. They are mechanically linked to the handle but electrically isolated from each other. The two Commons are “not” wired together.
You can get latching and momentary versions too. The latching stays in the position you switch it to. So you’d use that type for controlling the power (enable pin). The momentary is only engaged while you hold it in position. Take your finger off and it goes back to its at rest position. Like a doorbell button.