1 Reply Latest reply on Aug 16, 2019 3:26 AM by celcius1

    My Retropie Portable Build


      Hey Guys,


      I've decided to discuss my Retropie Handheld build, I would love feedback if it is constructive, now I had a 7" RPi touchscreen lying around, and decided to build it into a Retropie portable, now power requirements, had to be considered, now Powerboost chargers from adafruit wont cut it with the current feed needed for the RPi 3B+, so for the Power source, I'm using 4 LiPo cells, with a capacity of 4000mAh, wired as two packs, so i have two packs with an output voltage of 7.2v and then in parallel so I have a battery capacity of 8000mAh.  I also cant use Adafruit stuff as there are no local stockists of the modules here in Adelaide.


      But with the charging circuit I've modified one I found for charging 4 cells that uses an ATMega328P, the changes I'm making is for charging 2 cells even though I'm using 4, I am assuming I can treat the two packs of two cells as two cells to the circuit.  The other change is to add a means to switch from battery power to PSU when it is plugged in for charging. and load share between the pi and battery, the power from the PSU or battery then goes into a Buck Converter, (https://www.altronics.com.au/p/z6334-dc-dc-buck-module-3-40v-input/), so I can give the Pi and screen upto 2.5A at 5v.  Also I'll be adding a means to the battery charging circuit if a low battery condition is detected, so that it can signal the RPi to shutdown if the voltage drops below a set threshold.


      Now the reason for building my own charging interface is because here in Australia we don't have much in the way of standard modules, even ones with the power requirements of the RPi 3B+, plus I prefer a bigger handheld screen.


      This is the reference I am using for building my own version of the charging circuit https://www.microfarad.de/li-charger/ this site is quite informative, and will help in customising this circuit for my requirements.


      For the buttons I am going to use a basic key matrix, and take a page from the TBHS project where they did this, as its a good proven method of input.


      The batteries I am using https://www.altronics.com.au/p/s4761-26650-lithium-ion-3.6V-4000mah-rechargeable-battery/

      Controller I am using for charging https://www.altronics.com.au/p/z6222-sparkfun-dev-11113-pro-mini-328-5v-16mhz/

      Plugpack for External power and Charging https://www.altronics.com.au/p/m8936b-powertran-12v-dc-2a-fixed-2.1mm-tip-appliance-plugpack/


      I value constructive feedback of my project.


      I also forgot to add, once I get the handheld working, I'm going to look at expanding it so I can plug 2600 cartridges directly into it, as I have been working on a 2600 cartridge interface. running into a few hurdles, so focusing on something a little easier






      P.S. I'm umming and rring about actually recording this on video and doing a video of project.

        • Re: My Retropie Portable Build

          After speaking with my battery supplier, I've decided to go with 18650 Li-Ion cells, with 3 cells per bank, giving a battery voltage of 10.8V and battery life of approx 7hrs. as when the handheld is on battery it will draw approx 1.5amps per hour at a max draw of 2.5Amps at 5V, but this design change has meant that I'll have to change PSU type to a 15V PSU this is good as it provides a total of 2.4Amps which means if the unit was at max power draw, just under 1A will be draw by the Pi whilst on PSU and the remaining 1.4Amps are utilised for charging, and when the Pi is off the charging circuit will use the entire current range to charge the battery faster but I will implement a current sensing on the build so the charging circuit will draw the maximum current possible when available and in use.


          PSU I am now going with https://www.altronics.com.au/p/m89345-powertran-15v-dc-2.4a-2.1mm-fixed-tip-positive-appliance-plugpack/


          on top of this the battery technician I spoke to told me to focus on the battery conditioning part of the circuit too, to maximise cell life.


          Another design consideration, is i'll connect the UART from the arduino to the RPi so I can monitor the battery condition but also have a path to update the firmware on the charge controller easily.  For now I'll use it as a firmware update path, and use a digital output on the arduino to the GPIO to trigger a safe shutdown when the battery voltage reads as a low battery.