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Which transistors do I use?

EK61

Jan 5, 2014
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I'm making a Atari Flashback controller (which is an NES controller on the inside) and want to replace the four press switches for the directions with a joystick. The joystick I have has two variable resistors which are at the middle position when the joystick is in the centre. If I connect the two variable resistors to the +5, then to both a PNP and an NPN transistor each, then I could use them to replace the switches on the original NES controller circuit design. (That is, 2 PNPs and 2 NPNs, one of each per variable resistor)

If this is all good, then what transistors will I need to use?

I have a few stray ones, but will probably need to buy some, unless I can find some in old circuit boards.

I can further explain the project if necessary, or if you are just interested.

Thanks for any replies.
 

Old Steve

Jul 23, 2015
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Maybe I'm just slow, but I can't picture exactly what you mean.
Can you draw up a schematic diagram and scan it, rather than trying to explain in words?

I guess you're talking about connecting the NPN / PNP pairs as push-pull drivers, but still can't picture your connections.
 

EK61

Jan 5, 2014
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It's pretty badly spaced, but...
joystick_zpsxwhahhwl.png

U, D, L and R connect to the +ve terminal where the press switch would be. (Up, Down, Left and Right) The grounds go to, well, the ground, as the -ve terminal would do on the switch. 7 connects to the +5V on the controller connector.

So this circuit would replace 4 switches on the stock NES controller. The basic NES switches would just go R-GND, L-GND, U-GND and D-GND respectively.

Is this enough, or do I need to post the whole circuit diagram, if the connections are too hard to follow?

Note: I may not know what I'm doing...
 

Old Steve

Jul 23, 2015
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It's pretty badly spaced, but...
joystick_zpsxwhahhwl.png

U, D, L and R connect to the +ve terminal where the press switch would be. (Up, Down, Left and Right) The grounds go to, well, the ground, as the -ve terminal would do on the switch. 7 connects to the +5V on the controller connector.

So this circuit would replace 4 switches on the stock NES controller. The basic NES switches would just go R-GND, L-GND, U-GND and D-GND respectively.

Is this enough, or do I need to post the whole circuit diagram, if the connections are too hard to follow?

Note: I may not know what I'm doing...

Already, I see a couple of problems.
1. Are you sure that the original switches actually switch to ground? It's more common to see switches like those connected in a matrix for a micro to scan, in which case you'd need some sort of 'floating' switches, perhaps CD4016 or CD4066 analogue switch ICs.
2. Even if the switches did switch to ground, the voltage from +V through the pot to the transistor bases would keep the NPN transistors permanently switched on, regardless of the pot's wiper position.

In summary, you need to re-think your plan.

Edit: If you want varying voltages from the wipers of the pots to trip the switches, you'd need comparators to measure the pot voltage and trigger at a preset voltage. And you'd need one end of the pots connected to +V, with the other end connected to GND.
 
Last edited:

Harald Kapp

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want to replace the four press switches for the directions with a joystick. The joystick I have has two variable resistors which
Get a joystick with built-in switches.
 

EK61

Jan 5, 2014
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They do all go to ground. Yeah, I thought it may be wrong. Thanks for the help. A joystick with built in switches would be a good idea. Do they have a specific name that I could search for?
 

Old Steve

Jul 23, 2015
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Last edited:

EK61

Jan 5, 2014
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Thanks. I saw one like that on Ebay. I'll have a good look for one some time, but I am very busy at the moment, so this project won't be completed for a while.
 

EK61

Jan 5, 2014
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I might be doing a few practice projects and little things before I attempt this. Haven't soldered for a while, and my skills have escaped me. I tried the other day: burnt myself twice and generally had great difficulty (didn't mess anything up amazingly, I did accidentally connect two points next to each other but managed to fix it.) But I have done some good things before, so with practice I should be back to skills.

The main problem is that I don't have any decent equipment. I really should get a holder for the board. When I used to do it at my grandparents I used to put it between the boards on the folding workbench, as in one of these:
d6f83f50-9a3a-4da6-91b8-e66d756bed91.jpg

But this time I don't have access to one. I'll definitely be buying a PCB holder.
 

Old Steve

Jul 23, 2015
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I just use a blob of Blu-Tak to hold boards still while I attack them.
 

EK61

Jan 5, 2014
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That's brilliant. Thanks. My solutions was clamp it to the bench (with rubber between the clamp and PCB) and when there was no room on the board any more I clamped a crocodile clip to the bench and held it with that. Blutack is a much better idea.
 

Old Steve

Jul 23, 2015
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BluTak's a great invention. I use it for a lot of things, like what I'm doing right now:-
100_6210.JPG

That's a Mattel Mindflex headset, with components too small to see. (For me, at least.)
 
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