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My Retropie Portable Build

celcius1

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 image

 

Regards

 

Paul

 

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

Top Replies

  • in reply to celcius1

    Hi Paul,

    Each input that is connected to a switch needs a resistor (in your case a pull-down resistor, such as a 10 k resistor) otherwise each input is floating until a switch is pressed.

    Is the requirement to have the Chip select be normally low, and then to go high when accessing the chips? If so, you could wire it to any other pin on the Pi and manually set it. Or, just permanently wire it high if that works for your circuit (I have not checked). Also, 100nF capacitors are needed.

    Use what you're most comfortable with, I just personally feel using a library like wiringPi is far reduced coding (and more reliable) compared to trying to access BCM.. registers manually.

    Also, no matter how confident you are, I'd suggest just buying a few of the ICs and trying it out, rather than buying a tube of 50 if there's a risk your design may change and use a different device. ebay Australia (I would not normally suggest ebay, but if you're struggling to obtain fewer quantities from a distributor) has them in single quantity: https://www.ebay.com.au/itm/74HC165-8-bit-parallel-in-out-Shift-Register-IC/254545886099?epid=1963682493&hash=item3b441d…

  • in reply to shabaz

    The Clock Enable is Active Low, and when it is pulled low starts clocking the data out serially on the rising edge of pulse.

     

    And I have investigated manually clocking out the data using the GPIO and not the SPI protocol, but it adds a lot more to the code, which I can do, but SPI can read the data in approx 6 microseconds whereas if I code it manually and ensure the slowest delay time of one microsecond per data read I’m looking at approx 40 microseconds to read the data but in thinking that thru, it’s still a short space of time, but I still need to poll the registers.

     

    Also if I increase the component count again, I can use shotky diodes to tie, all the input lines to a single GPIO pin looking for a button push, and essentially give me an interrupt. But prevent the other lines from being affected.  As much as I could interface a standard row and column approach, I want to keep the amount of GPIO I use to a minimum if I need more in future if I use the same 32 button input hardware.

     

    ill do a bit more work, and clean up the schematic and I’ll also write the code that handles the data scan manually using wiringpi


    i Didn’t mind buying the tube and the IC is a standard one for adding in more inputs, so don’t worry I’ll end up using them. And the tube only cost me $25

     

    its late here I’ll do it during the day, bed time for me

     

    Regards

    Paul