Old 15-01-2016, 11:22 AM
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AndrewJ is offline
Join Date: Mar 2006
Location: Melbourne
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Joystick design

Gday All

Need some low level electronics help.
I am repurposing a bulky old joystick into an EQMod controller that i can hold in one hand.
I have bought a new small ( thumb operated ) joystick assy and have started designing how to fit it to the old controller.
The old joystick used a CY7C63000A-PC chip, and as such, it has to manually read the pots by timing the charge time of an RC filter.
The specs say that a std joystick uses a 100k pot
which feeds a 2.2k resistor and then a 1500pf capacitor to ground.
ie +5V - pot - 2.2k - tapping - 1500pf - gnd
The tapping between the resistor and capacitor then directly feeds the pin on the controller, which does the time calcs.
My new joystick uses 10k pots, so i know i need to redesign the values of the RC filter to get equivalent time constants, but whereas "the book" states that you go directly to the controller pin, my old joystick used a 1n4487 diode here. Notwithstanding this will give a forward voltage drop that will affect the trip points, a 1n4487 is an 82V zener????
It is fitted forward biased, so is operating as std diode,
but why the hell would it even be fitted????????
Why pick such an oddball size?????

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Old 15-01-2016, 12:22 PM
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billdan (Bill)
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Gooday Andrew,

The diode is probably there to protect the chip from reverse voltage across the pot. But you could use any run of the mill diode for this purpose, as to why they used a relatively expensive Zener is beyond me, unless they got them dirt cheap on Ebay.


EDIT: Unless you are supposed to reverse bias the diode and it acts as a voltage regulator, providing a regulated voltage of 8.2V (82V sounds unlikely) to the chip. No that wouldn't work if its in series.

Last edited by billdan; 15-01-2016 at 12:28 PM. Reason: more thoughts
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Old 15-01-2016, 03:39 PM
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AndrewJ is offline
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Location: Melbourne
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Gday Bill

Not sure ebay was running when this joystick was made :-)

Its definately a forward biased 82V zener ( hence part of my confusion ).
It seems weird to use it here, as it lowers the final voltage into the chip, ( it measures as a 0.545V forward drop ) and this will alter the timing to the (unknown) trip point. As the chip is actually running a program to read the pin, i think i will still need to leave the zeners in there, but finding the exact units is not simple.
I think i will end up doing a simple trial and error once i get the RC circuit right, but would be interested as to why a diode got used here.
Everything is 5V from the USB power so no idea where 82V could come from :-), and as its a well known brand, i have to assume they did it for a reason.

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Old 15-01-2016, 03:46 PM
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Merlin66 (Ken)
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As you probably already know from the EQMod forum, I'm the BOF who would prefer to have a "push-button" controller....
I understand what you are currently doing, but does it go anywhere close to be able to be replicated to make a small EQMod handcontroller a reality for the others?
What are the options?
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Old 15-01-2016, 04:26 PM
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AndrewJ is offline
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Gday Ken

What im doing now is probably very specific, as the joystick i have
( a Futuretronics BlackHawk Mark 2 ) appears to have custom pot reading, and only has 4 buttons.
The recent posts on the forum show how others have repurposed the guts of game controllers to make multi button boxes, but again, each one requires specific knowledge of the board being used and a large box.
Its not difficult, but each one needs to be looked at on its merits.
Thats why i was so impressed with the raw USB controller from pommyland.
Its a tiny footprint, and has "sticky" USB mapping, so swapping ports doesnt keep remapping it.
If you dont want to use potentiometers or any fancy wiring / top hat functionality, you could natively map up to 12 buttons by simply taking a wire from each switch to the board, and from all switches to ground.
Thats it
If you want the other functions, its also very simple, and as his unit uses accurate onboard ADC units to read the pots, none of the drivel i am going through at present is required.

I havent actually enquired as to if he is still in business, or what shipping to Oz is etc, but i have seen lots of posts on other forums re gamers etc making custom controls using his units, and all were happy.
Best of all, no windows drivers reqd to get it going.


Interesting how many people who prefer buttons or joysticks came out of the woodwork after my original post re not really liking game controllers
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