Cassidy Nolen Posted November 3, 2008 Share Posted November 3, 2008 All, Some of you saw my handheld based on the FB2 as the brains. Its a neat little machine...with one evil exception... The hardware required I put a selector switch between the fire button ports for the paddle and the joystick games. It ends up that the extra wire (about 10 inches total) is getting a TON of RF interference when the game is assembled. As long as you don't screw the whole thing shut, it works fine. As soon as you do, its an issue. I have rewired a ground wire to run next to it (to act as a silencer), used a ferrite slug wrapped around the wire, but nothing I have done has worked. New wire, checked solder joints for overlap, nothing. The "fire" button wires had to be run behind the monitor. In other words, the D-pad buttons are pretty close to the actual PCB, so I dont have a problem over there. Basically, wondering if I could put a capacitor between ground and the fire button (or one of the two fire "pins") to silence this thing up. It is my thought that something like 220mfd cap (5V) would help get any RF noise in there quited down. Literally, if you touch the outside of the wire insulator, it fires the game. Crazy. Most games at this point are unplayable. Any and all help would be appreciated. Thanks in advance, Cassidy Quote Link to comment Share on other sites More sharing options...
+poobah Posted November 3, 2008 Share Posted November 3, 2008 All, Some of you saw my handheld based on the FB2 as the brains. Its a neat little machine...with one evil exception... The hardware required I put a selector switch between the fire button ports for the paddle and the joystick games. It ends up that the extra wire (about 10 inches total) is getting a TON of RF interference when the game is assembled. As long as you don't screw the whole thing shut, it works fine. As soon as you do, its an issue. I have rewired a ground wire to run next to it (to act as a silencer), used a ferrite slug wrapped around the wire, but nothing I have done has worked. New wire, checked solder joints for overlap, nothing. The "fire" button wires had to be run behind the monitor. In other words, the D-pad buttons are pretty close to the actual PCB, so I dont have a problem over there. Basically, wondering if I could put a capacitor between ground and the fire button (or one of the two fire "pins") to silence this thing up. It is my thought that something like 220mfd cap (5V) would help get any RF noise in there quited down. Literally, if you touch the outside of the wire insulator, it fires the game. Crazy. Most games at this point are unplayable. Any and all help would be appreciated. Thanks in advance, Cassidy replace wire with a piece of shielded cable? Quote Link to comment Share on other sites More sharing options...
Stephen Moss Posted November 4, 2008 Share Posted November 4, 2008 I concur with poobah, try using screened cable such as mini co-axial or microphone wire and earth the screen at both ends. As for the 220mfd capacitor did you really intend it to be millifarad which would be massive or did you mean microfarad (uF)? In either case if your use of the tern RF is correct then you need a small decoupling capacitor such as 0.1uF. (100pF) or less it really depends of the frequency of the interference. Quote Link to comment Share on other sites More sharing options...
Cassidy Nolen Posted November 4, 2008 Author Share Posted November 4, 2008 .1uf is much closer to what I meant to say. I did not know what to even begin to guess. RF is really what I am talking about, and I like the idea of grounding both ends of the shield, had only grounded one. Will a .1uf complete the circuit, causing the button to seem "pushed down"? Thanks for the suggestions, I really do want to get these things finished. Cassidy Quote Link to comment Share on other sites More sharing options...
+batari Posted November 4, 2008 Share Posted November 4, 2008 Basically, wondering if I could put a capacitor between ground and the fire button (or one of the two fire "pins") to silence this thing up. It is my thought that something like 220mfd cap (5V) would help get any RF noise in there quited down. Literally, if you touch the outside of the wire insulator, it fires the game. Crazy. Most games at this point are unplayable. I'm not sure that's RF. It seems unlikely to me that RF would be so bad that it would "press" the button for you. Sounds like a short somewhere. Quote Link to comment Share on other sites More sharing options...
BigO Posted November 4, 2008 Share Posted November 4, 2008 (edited) .1uf is much closer to what I meant to say. I did not know what to even begin to guess. RF is really what I am talking about, and I like the idea of grounding both ends of the shield, had only grounded one. Will a .1uf complete the circuit, causing the button to seem "pushed down"? Thanks for the suggestions, I really do want to get these things finished. Cassidy A capacitor effectively blocks DC and conducts AC. So, in theory it shunts the AC to ground without affecting the DC that's passing through the same wire. That's a first approximation, but it's effectively what will happen in this application. [edit] Oh, and if you connect the capacitor to the circuit while it's already live, it could (very briefly) bring the potential of that line to ground. I would guess that a cap that small probably won't pull it down long enough for the console to catch it. Actually, it may somewhat clean up the signal going to the console (not that it necessarily needs it) A capacitor can be used to to do simplistic "debouncing" of switches. Edited November 4, 2008 by BigO Quote Link to comment Share on other sites More sharing options...
Stephen Moss Posted November 5, 2008 Share Posted November 5, 2008 Will a .1uf complete the circuit, causing the button to seem "pushed down"? It depends on the circuit design, if the circuit consists of a resistor to the supply voltage and a switch to connect it to ground when pushed then the capacitor will effectively be in parallel with the switch. When the switch is released the capacitor will take some time to charge through the resistor (IIRC 0.6x CR to 2/3 supply, 1.6xCR to supply) which will be about 800uS max if the resistor is 5K0 so I doubt that you will be polling the switch fast enough to notice it as it is to fast for switch debouncing which generally needs a charge time of at least 10mS. Quote Link to comment Share on other sites More sharing options...
BigO Posted November 5, 2008 Share Posted November 5, 2008 Will a .1uf complete the circuit, causing the button to seem "pushed down"? It depends on the circuit design, if the circuit consists of a resistor to the supply voltage and a switch to connect it to ground when pushed then the capacitor will effectively be in parallel with the switch. When the switch is released the capacitor will take some time to charge through the resistor (IIRC 0.6x CR to 2/3 supply, 1.6xCR to supply) which will be about 800uS max if the resistor is 5K0 so I doubt that you will be polling the switch fast enough to notice it as it is to fast for switch debouncing which generally needs a charge time of at least 10mS. True, it is a relatively teensy capacitor for debouncing, but it should eliminate some amount of the noise, teensy amount though it might be. Yeah, it doesn't really need debouncing. I've never heard of anyone having problems and I personally have hooked up things where I was just plugging a wire into a breadboard and pulling it out without any apparent bounce. It really is negligible in this situation, I just tossed it out there while we were in the neighborhood. Quote Link to comment Share on other sites More sharing options...
Cassidy Nolen Posted November 6, 2008 Author Share Posted November 6, 2008 I'll get on that this week. Thanks to you all. It really stinks that I have made two identical and they BOTH have the EXACT same problem as soon as you push the two halves together. Everything else is well insulated, sealed, etc. so I am 99.9 sure its RF. I can't hurt anything doing this, you know? Might as well try out some caps. Thanks again, I will also rewire with some shielded wire. Off to get some this next week.... CN Quote Link to comment Share on other sites More sharing options...
BigO Posted November 6, 2008 Share Posted November 6, 2008 (edited) I was skimming back through this thread and something struck me while reading batari's comment about it being unlikely that RF is causing it to "push the button". Did you hack up the PC board at all? It could be that if you removed a pullup resistor from the circuit, you've got a "floating" input to a logic gate. Such a condition can very easily cause the erratic behavior you're describing. With short wires and a bit of luck, it might be fairly stable and appear to work fine. When you extend that wire or put it in proximity of certain other materials or signals it could be picking up just enough noise to trigger the gate. I don't know the logic technology used in the FB2 nor do I have the schematic to reference. But, the original 2600 schematics do show a pullup resistance on pin 6 (joystick fire button) of the controller port and a 470pF cap that would filter noise just as was discussed above. If you did hack away that bit of the FB2 board, it's possible that just adding back a pullup resistor could resolve your issue. Edited November 7, 2008 by BigO Quote Link to comment Share on other sites More sharing options...
Cassidy Nolen Posted November 10, 2008 Author Share Posted November 10, 2008 Man you guys are smart....seriously, I have the greatest respect for the group knowledge on these boards. I really do appreciate your help on this, BigO and everybody else. Indeed I did hack the board, but not to remove a single piece. Assuming the Stella designs were followed somewhat truthfully, that part would make sense. I have a hard time beleiving I had 2 of them identically wrong, so I am assuming its not my handiwork (which I might add I thought was pretty decent on these projects). This would make sense. 470pf it is. Will get a few, I am sure they are cheap! Cassidy Quote Link to comment Share on other sites More sharing options...
BigO Posted November 13, 2008 Share Posted November 13, 2008 Get some detailed pictures of the board and assembly if you can't get it working. I'm curious about what you had to hack on the board without removing anything or losing any traces. Did you just fold it over on itself? Quote Link to comment Share on other sites More sharing options...
Cassidy Nolen Posted November 13, 2008 Author Share Posted November 13, 2008 Get some detailed pictures of the board and assembly if you can't get it working. I'm curious about what you had to hack on the board without removing anything or losing any traces. Did you just fold it over on itself? Theres quite a bit of dead space on the ends of the board. I was able to cut them off, remove all switches (bypass difficulty completely), pass capacitors through to the other side of the board and then fit into the handheld. I'll get some pics when its apart this week. Thanks again, Cassidy Quote Link to comment Share on other sites More sharing options...
Cassidy Nolen Posted November 23, 2008 Author Share Posted November 23, 2008 ITS ALIVE!!! Everyone, thanks for your help. BIG O, you are THE MAN! I really appreciate all of your help on this. I simply wired a 470pf cap in parallel with the Fire pin and a separate one with the Right directional pin (fire when the switch is in "paddle" controller mode) and this got it working 100%. I knew it was not a bad solder joint, all you had to do is touch the insulation on the wire and you were triggering the fire button. Both paddle and joystick games work great. I will get some pics inside when I do mine. This one has to go to its new home tomorrow (I owed this fix for a LOOOONG time). Thanks again, I really appreciate everybody's help. You are all seriously smarter than me.... Cassidy Quote Link to comment Share on other sites More sharing options...
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