Worklog Q*Mini Arcade Game Redesign

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A couple of years ago, I bought a miniature handheld arcade machine featuring the game Q*bert. Recently, I saw it in my closet, and thought, "hey, you know what, that thing isn't very comfortable to play, why don't I redesign it!" So that's what I'm going to do. In total, I'm going to:

Design and 3D print a case reminiscent of the GBA.
Replace the "joystick," which is internally just a d-pad, with an actual d-pad.
Create custom PCBs for the button and d-pad.
Design and 3D print d-pad, main button, and power/sound buttons.
Relocate the button and d-pad to the sides of the screen.
Add a couple Li-Po cells and a micro-USB charging port.

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I wanted to post some pictures of the internals of the machine to give an idea of what it looks like, as well as the size of it. (there is a lot of wasted space inside of it.) Also, I forgot up until now that I was supposed to put a card in the pictures with my name and the competition and whatnot, so I'll try to start doing that now.

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I was wondering about this little bit attached to it. The pads it is connected to are labelled "try me," and I'm not sure (I bought it used at a thrift store), but I think that may have been where the little tab was at. You know, the one that all electronic toys you buy at the store have that you're supposed to pull out before using it but sometimes doesn't seem to do anything. Anyway, I thought perhaps somebody more knowledgeable than me could let me know if it was safe to remove.
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That little box, in the original machine, is flush with this slot on the back:
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I just got some muriatic acid I had ordered, so I'm ready to start making the custom PCBs. I also found a small piece of solderable breadboard I had, and I am going to be using that for the main button, but a custom PCB for the d-pad. I've also been working on refining my case some more, and I am going to be adding in mounts for the buttons, boards, etc. I'll post pictures when that's finished.
 
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Nice idea! That little thing is a circuit detach switch for detaching the batteries before use. You can see that by inserting a small piece of paper/plastic and see that it opens the circuit. You can remove it although you will need to bridge the two pads (I think). See if it works without bridging them and if it doesn't, then bridge them. Wish you good luck!
 
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I'm still in high school, so I don't have much of a budget, and therefore haven't been able to buy everything I need yet, but I have been able to order some stuff from Amazon, and today my pack of 10 battery charging boards came (it was like $6). I measured their output, and they are outputting ~4.2v, so I decided to use one to power the Q*mini. I also removed the little box and bridged the two pads, per @Commandblock6417's suggestion. I am happy to report that it is working great!
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This is what I currently have as far as charging the batteries and connecting them to the Q*mini. As I am inexperienced, this may not be the proper way of doing this. Since the charging board outputs ~4.2v, it won't be able to go through the regulator. I would like to implement some sort of thing that will disconnect the batteries and regulator when plugged in and turned on so that it can be powered directly from the charging board, but I'm still trying to figure out how to do that. I have an idea of how to do it, but I am not yet able to test it. I'll see what I can do and follow up later. Hopefully I can figure it out, and stay on my limited budget. Me not having a job is another reason I wanted to do this project: It's a lot cheaper than a Wii portable.

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I have updated the schematic for power management in the Q*mini. I am going to implement 1 port charge or play. In other words, if the portable is turned off, plugging it in charges the batteries. If it is turned on, it gets power from the batteries, or the board if it is plugged in. If it is plugged in and turned on, the batteries and regulator are disconnected. I split up the components controlling this into three groups to make things easier to see.

The group outlined in blue connects the battery charging board to the Q*mini ONLY if it is plugged in AND turned on. The group outlined in green disconnects the battery from the charging board ONLY if it is plugged in AND turned on. The group outlined in red turns off the regulator ONLY if it is plugged in AND turned on.
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However, all of this is in theory, as I haven't yet had a chance to test it. I still need to buy the regulator, which I will be able to do soon. As far as the diodes, resistors, and transistors go, I will be able to get those later. Sometime this month, after graduation, I'll be able to get back into my school to pick up any tools and stuff I left there. My PLTW teacher has a ton of components of every sort, so should be able to get them from him. Once I have everything, I'll breadboard it and make sure it works.
 
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I’ve removed the PCB for the button and d-pad and replaced them with my own. Contrary to the current 3D model, I’ve decided to move the d-pad to the right side of the screen because (1) I’m right handed and (2) it’s easier to solder it that way. At first, it was a big hassle. I was using regular wire and a thicker solder, not to mention a pretty crappy soldering iron. A lot of the pads were getting bridged, and it was in general pretty bad. I was going to take a picture of it, but I forgot. However, my 28 AWG magnet wire and .3mm solder came from Amazon, and I got my soldering iron back from school (which still isn’t that good, but at least I have replacement tips for it), so I decided to take another crack at it. Aaaaaand... It works! Kind of. It’s got some wire spaghetti, and I wired the d-pad pins in such a way that I have to turn it 90 degrees to get the orientation right, but I’m going to redo it later on anyway to give it more room to move so that it fits in the case. For now, though, I’m happy with it, especially for my first “real” electronics project.

Also, I unfortunately wasn’t able to get the components for my charging setup from my teacher, so I’ll have to buy them. Fortunately, they shouldn’t be too expensive.

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When I was using my crappy soldering iron, one of the pads started to pull up, so I used electrical tape to stick it down:
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vikMKW

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You have great enthusiasm, and that will go a long way. Lithium battery technology is a very complex field. Battery University provides credible and free information on this. I strongly suggest reading through the lithium classes. Some topics to learn about include: capacity vs voltage, charging, over-discharging, cells in parallel, cells in series. Without paralleling cells, the battery life will be very low, so make sure to look into cells in parallel.

The TP5046 is a nice elementary charge IC will charge your cells to ~4.2 using constant current then constant voltage (see Julian Ilett's video), but the Li Ion cell voltage will drop as its capacity decreases. You risk damaging the cell if the voltage drops too low, so you want to cut off power before the cell reaches that threshold. This can be done using compactors, ADCs on microcontrollers, or through designated voltage monitoring ICs.

I noticed that you have a 655 Ohm feedback resistor, which I understand is to achieve 4.5Vout. The PTH08080 is a buck (step down) converter, which means your output cannot exceed your input voltage. The cell's voltage will drop from 4.2V as your electronics draw current from it. The regulator's output will drop linearly following the cell voltage; in fact, you won't even see 4.0V out of the regulator with a fully charged cell. Rule of thumb is that you should not demand an output voltage from the regulator that's higher than the cutoff voltage (~2.5V for li ion) of your battery.

If you want 5V output from a single cell, you'll need a boost converter like the Powerboost 500C from adafruit. Another solution is to put 2 cells in series, which will double your voltage, and then you can use the PTH08080 to step down the voltage to a solid 5V. The trade off is that the supporting circuitry becomes more complex because now you need to balance charge and monitor the cells.

There exist ICs that balance charge cells, boost output voltage, have integrated over-discharge protection, short circuit protection in one package. They will require some active and passive components too. Their upfront cost may seem high, but they will save time reinventing many wheels, and parts that will be destroyed in the learning process. Take a look, and definitely ask questions!
 
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Thanks for the info. I am planning on using 2 of these Li-po batteries in series, which I think should fix at least a couple of the problems you mentioned (though I clearly don’t have a lot of experience, so don’t quote me on that). Thanks for pointing me to those resources, though. I’ve been trying to find some good information about batteries since I don’t know too much about the subject, so I’ll definitely check those out!
 

vikMKW

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Power is not easy! You're almost replicating a laptop power system, but with a 1 man band. Usually there's a whole team.

Running those lipos in series means you'll need a board like this to properly charge them + a PTH08080, all while not increasing your capacity.

Does that system run off 5V? If so, then 1 battery paired with the powerboost 500 is likely what you need: https://www.adafruit.com/product/1944
It looks like that console won't demand too much current, so you might get away with the 1200mAh lipo you linked. I assume you're using them because they're flat. 18560s should still fit in the case comfortably while having almost 3 times the capacity for half the price. Think about it.
 
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Does that system run off 5V? If so, then 1 battery paired with the powerboost 500 is likely what you need: https://www.adafruit.com/product/1944
...
18560s should still fit in the case comfortably while having almost 3 times the capacity for half the price. Think about it.

Well, you've essentially rewritten my BOM and not only made it 5x shorter (it’s only two things now) but also 2x cheaper. Many thanks! However, the PowerBoost 500C is out of stock, so will I be able to go with the PowerBoost 1000C with this battery?
 
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vikMKW

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Again, you're certain the system runs off of 5V?

Aside from the hefty price, the powerboost 1000C is a superb option. If you hook up a switch between EN and GND, that's your power switch right there. You can desolder the SMD low battery indicator LED next to the JST-PH connector and wire your own LED anywhere in the case (watch this video). It'll take care of all your protection and voltage monitoring needs.

The battery you linked is good. I suggest pairing it with a battery holder (shop around for cheaper sources). Those cells are meant to be spot welded to a conductive strip, but people don't typically have spot welders lying around. You'll see people solder wires to the ends of the cell (been there), but that's not good practice. You'll get a cold joint and you run the risk of damaging the cell from prolonged heating. Plus, you make it serviceable in case the cell goes bad at any point.
 
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The system originally ran off of three AA batteries in series, giving it ~4.5V, though as mentioned before, using the TP4056 charging boards I bought I was able to run it off of ~4.2V. If you think that 5V is too much of a step up from there, then I guess I’ll look for something else. Also, I’m planning on buying an 18650 battery holder from Mouser to mount the battery in the portable.
 
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Alright, so... I done borked. :facepalm:

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A bunch of the stuff I had ordered from Amazon came yesterday. I had a virtual graduation party over Zoom with my family and friends recently, and a bunch of people sent me some gifts, including many Amazon gift cards, which I put to good use. I purchased a Weller 1010NA soldering station, a nice solder rework station, the PowerBoost 500C (turns out they were in stock at Amazon), a battery, someone gave me this multimeter I wanted, etc. Today I was wiring up my battery to the PowerBoost, and I was testing it to make sure it was working properly. It was. I figured I should make sure that nothing was getting hot or anything like that, so I used the thermometer in the multimeter. That's when the problem happened. I had been testing the voltage of the battery with these hook leads that have a hole on the back in case you want to plug in something else along with them.

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I figured that was perfect because I could plug in the thermometer too instead of having to switch between the two leads. However...

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In the thermometer, the red and black plugs are directly connected. In other words, as soon as I plugged them into the multimeter, power and ground were shorted together, and the bright yellow charging LED went extremely dim. That was the moment I realized I had made a terrible mistake. I unplugged it immediately, but the damage was done. I tested the battery, and fortunately, it seems to be working fine, but the PowerBoost is definitely done for. Whenever it is plugged in and the battery is connected, this chip jumps to over 100 degrees in less than a second.

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So now I guess I'll have to buy another PowerBoost. ¯\_(ツ)_/¯
Oh well.
 

cuyax

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Potentially you can replace that regulator that you pointed out on the PowerBoost. Here is what I could find from the Adafruit schematic

It's essentially the battery charging circuit. It's found in a bunch of other products...
 
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I’ve already ordered another PowerBoost, so I’ll just stick with that. Thanks, though. At this point, I’m not sure if I trust my soldering skills enough to try and replace that chip.
 

vikMKW

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The ability to make board corrections, is an important skill to develop. I suggest to order the part and try it. You have nothing to lose, and you'll gain a powerboost for other projects if you succeed.
 
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Alright, why not? It’s not like I can make it work any less than it already does, right?
 
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