Planning a protable Velleman MK191

[the antithesis]

I'm planning to turn my Velleman MK191 Classic TV Tennis Game with Analog Bats into a semi portable pong system by implementing a screen and 3D printing a case.



For those unfamiliar, the MK191 is a soldering kit.

I'm not entirely certain how to attach the screen since the screens we use run on 5v and this only uses 3v from the two AA. Should I get something like the Adafruit PowerBoost to achieve 5v? Should I replace the power altogether with a lipo because the drain on 2 AA would lead to short battery life? Any help is appreciated.

[the antithesis]

So I have managed to hook up a screen. It works and I learned a bit.



As you can see, I have an adafruit powerboost and a lipo battery attached. I had tried to hook the screen up directly and it worked, but the screen would flicker badly. I think it just didn't have the juice to run the screen with two AA batteries what it was doing is powering on and off. I added the PowerBoost which seemed to work better at first, after a few seconds of flickering, but it a little later it would flicker again, remaining stable for only a minute or so. So, I put the lipo battery in and removed the AA's and it works. The whole unit even powers off when I power of the game's main power-- it has a soft power button that you hold a few seconds to switch it off.

My main concern was the main board is only supposed to have 3v and I have 5v running through it, which could have been slowly frying the microcontroller, but I looked up it's data sheet and it has a range of 1.8 - 5.5v. I'll test putting just the battery in the circuit w/o the Powerboost to see if it's like the MintyPi and can run straight off the battery power. The screen nearly worked using two AA's so the lipo which is a bit more powerful (about 3.7v IIRC) might not need to be boosted to 5v.
EDIT: It works. So I only need the Adafruit Minilipo

Once that gets done, I'll also have to hook up the small amp I have and a speaker from one of those annoying birthday cards that plays a song.
EDIT: Got it working. This is a situation where a piezoelectric beeper would have been appropriate, but I got this speaker for free. The amp has an on/off volume knob and for some reason I just couldn't get it to shut off. I think it's because the power and signal were both coming from the main board so when the knob opened the circuit to shut off the amp, the signal circuit still sent enough power to keep it running. Shut off, it was louder than the lowest setting when on, which is weird. So I attached the speaker directly to the main board and it works. I could experiment some more with the amp or just save it for another project as it wasn't that loud, anyway. I may put a small switch in line with the speaker as a mute function because I'll bet the beeps get annoying.

I am still wondering it it'll be worth my time to rig some kind of switch that will shut off the screen and amp when you plug the until into a TV using the RCA jacks. I like the idea of the built-in screen and audio cutting out when you hook this up to a TV, but that may not be necessary and more trouble than it's worth. It may be impossible. I'll have to double check my circuit. I may have this drawing power from the screen, so shutting it off might break the whole power circuit.

In any case, this is a real sense of accomplishment. Once I get the innards working the way I like, I get to design and 3Dprint the case.

[the antithesis]

Okay, I have an actual question with which, hopefully, someone can help me. The audio amp I'm using I got at Wal-mart out of a device for kids' bikes so they can listen to their MP3 players. The problem is the signal in/out is supposed to be a separate power supply from the main amp circuit. When I hook this up to the game, turning the amp off using the on/off volume knob does not turn it off. Sound still comes out of the speaker. T tested it by rigging a separate power supply using some AA's and it worked perfectly.

So my question is, is there a way to sequester the amp inputs using the same power supply? I'm thinking diodes, but I may be wrong about that. I'd rather not have to use two sets of batteries if I can avoid it. I've taken photos of the amp board if that will help.



The contacts are labeled V+, GRND, SP+, SP-, IN+, IN-, V-. I am fairly certain the V +/- is supposed to be the main power circuit for the amp as this in the connection broken by the switch. SP+/- is the speaker. In +/- is the input. I'm not positive what the ground is for, but I think originally (it's been a while) the In +/- took in the right and left channels and made it into a mono signal, but I may be wrong.

Here's the back of the board to show the traces.



Thing is, the way I have the screen hooked up, I don't want to have a second power source to use the amp. The screen only has the one ground contact and this may screw things up or simply not work because of how the screen is attached. I would want to use the AA's on the main board since it already set up for it, but then the screen won't work or hooking the screen up to the lipo will just combine these circuits and then the amp will still have the same problem.

I'm thinking of hooking up the V +/- and just the In+ since it can use the V- as ground and attach a diode to the In+ to keep it flowing one way so it doesn't make a circuit when the amp is shut off. What do you think?

BTW, this topic isn't bugging anybody, is it? Lots of people have viewed but no one has said anything. I hope this topic isn't too annoying.

[abrugsch]

not at all. this is pretty nice! (and a welcome diversion from the usual)
I'm not sure what your problem is with re: the amp, but I haven't really fully grokked the setup yet. I'll have another look when I'm not just drive-by commenting while waiting for builds to finish at work...

[the antithesis]

Well, now's the time I make you all feel better about yourself.

I stopped by my local electronics store and picked up a diode. I put it in the circuit and it still had the same problem. Turns out I had gotten a zener diode which will do that. I was resigned to a second trip to the store when I recalled I had gotten some diodes a while ago, nice general purpose ones, and the worked.

Finally.

The one problem is turning on the amp rests the game. Not a horrible flaw but I can live with it. It doesn't rest it every time. I'll just have to not fiddle with the volume while playing, I guess.

So now I have the electronics fairly set. Now I need to design the case.

[the antithesis]

Minor update. I plugged the minilipo charger into the mains, (as Brits say, Americans say "into the wall" which sounds weird) to see if it'll run off that while the battery charged. It did, but the screen got the power cycling flicker again. I think the juice drops a bit when the charge cycle is engaged. If I want to be able to play this thing off the mains, I'll need to put the PowerBoost back, which may be better for the screen since it would give it the 5v it needs to really run instead of the 3.7 volts that allows it to run, but might explain some of the bugs I've noted above. (i.e. turning on the amp causes a reset probably because of the sudden drop in power)

I was kind of hoping to not have to use the PowerBoost so I could use it elsewhere. I'll need to decide if this functionality is necessary. Actually, I'll need to test to see if the PowerBoost would fix the problem. *Sigh* Well, I thought I was done with the electronics.

EDIT: the PowerBoost is necessary. The Minilipo charger has a preconditioning cycle when you first plug it in, which is when I tested it and got the flicker. I tested it just a little while ago when it's in the regular charging cycle and the screen was rock solid even when turning the amp on and off.

[the antithesis]

Took some video of the setup in action. I've added the switch from the Pigrrl kit from which I'm taking most of the power circuit.

You can see here when I turn on the amp (off screen because I am a terrible cameraman) that the screen and unit resets, probably because the amp's power draw is enough to drop the voltage. I'm trying to think of a way to fix this and I don't think there is. The amp has a common ground so any change would either mean the amp wouldn't work anymore or I'll have the problem with turning off the amp does not turn it off that I had before. One possibility is to have the main power come through the amp so it's a main on/off volume knob and use the switch in line with the speaker to mute it.

I also show the game is action and the computer kicks my ass. I am playing one handed but the computer usually beats me. Either I suck or the computer is alarmingly competent. Probably both.