analog to quadrature converter?

This is for a controller for a Pong game - the speed of the revolution would probably be comparable to that of a mouse, but the faster the better. A resolution of 255 pulses per revolution would be ideal...

Sounds pretty easy for a uC with an 8bit ADC. Every time the ADC changes a step, wiggle the appropriate wires. A 9bit (or more) ADC will give you a little hysterisis in the up/down motion without causing any loss in resolution.

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  Keith

Mad Scientist Jr skrev:

wouldn't it be a whole lot easier to replace the pot with something like this?

-Lasse

No, it's because of resolution and because of my interface (a hagstrom keyboard controller). I have an Atari 2600 driving controller plugged in currently and built a little paddle game, and the resolution of the driving controller is 16 pulses per revolution - you have to turn the dang thing 20 times to get the paddle to move across the screen, and I'm just drawing it in text! (5 chars on a 80 column textbox) ! In hires, it just won't do - to match the feel of regular atari pong/breakout the entire paddle needs to move across the screen in about 10/16 of one turn... with the screen resolution I am using, one pulse = a move of 4 pixels. with a screen of 640 pixels wide, that is

160 screen positions, if 160 is 10/16 of the total ppr, the encoder would have to be capable of 256 ppr. Ideally I would replace the encoder in the driving controller with one capable of 256 ppr, but mechanical encoders with that high res don't seem to exist (unless I'm looking in the wrong place). I think an optical encoder may be an answer, do they go up to 256? Also, I'm a programmer, I don't really know electronics beyond how to solder basic switches, so designing a circuit to drive an optical encoder may be beyond me. Also, cost is a factor, I want to spend as little as possible, ideally under $15 per controller. Anyway, a potentionometer to a DAC would take up 8 bits = 8 keys on my keyboard per spinner, which is too many inputs. With quadrature the paddle only uses 3 keys = 2 bits + fire button, which is good. A pot to a ADC to a PIC simulating quadrature at 256 ppr might do the trick and be cheaper than the hi res optical encoders (I have seen prices for those be $130 an encoder, no thanks)

Um, YES!

These optical encoders don't require any special circuits?

Do they go upto 256 ppr?

Alas, at $50+ a pop, they are kind of pricey and I see it only goes up to 160 ppr... However it is closer to a solution than anything I've seen

Keith's right, this could be done easily with a microcontroller, such as an 8-pin PIC with 10-bit ADC and internal oscillator.

Assuming you're talking to an ASIC with built-in debouncing for a mechanical encoder, you'd have to simulate minimum pulse lengths that were appropriate for such a device. That could limit the "slew rate" out of the simulated encoder, so it could take a bit of time to catch up with the shaft position if it is moved rapidly.

Best regards, Spehro Pefhany

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These are for pong paddles so I am not in a hurry to spend a lot of $. However, they look the right size and don't seem to require any circuitry. If I can find a 256 ppr one for less money that would work

I do not think a potentiometer will last very long. If the speed of the revolution does not change really fast you could use a hall sensor and a pll. If you are using a dc motor consider a ripple counter.

Josh

Mad Scientist Jr wrote:

So, if you can contemplate using a PIC and a pot, why can't you use a PIC and a lower res (cheaper) shaft encoder, measure the velocity you're moving the shaft and multiply the rate based on velocity? MS-DOS had mouse .INI files to do just that where you would specify the rate and multiply factor. Variable rate MIGHT work even better.

GG

you can get optical incoders in much higher res if you want. we have some at work that range up in the 1500 PPR. of course those are like a cube block. the link will show you something at 250 PPR

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Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

Is the reason for considering an analog pot instead of the available

360 degree rotating quadrature knobs because of cost?

Jon

Those are what I was thinking about in my prior comment. I have a bag of them with 64/rev, optical, and they were $6 each I think. And yes, I've seen them sell for something around $30 or so, which is why I bought them for later use. I wouldn't be surprised to be $50+ per. Which is why I was asking.

Jon

I'd think backlash/anticipation/hysterisis would be a problem with such a scheme.

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  Keith

damn, you cross posted AND multi posted!! please don't multipost, and be conservative with cross posts

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mehaase(at)sas(dot)upenn(dot)edu

Use a "digital pot" that outputs quadrature already- it's called an encoder, and it's not expensive. Bourns EAW0J-B24-AE0128.

Paul Burke

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Since you\'re a programmer, doing it with a PIC ought to be dead
simple.  Get one with an internal ADC, run it ratiometrically with
Vcc as its reference, truncate the ADC\'s lower order bits until
you\'re left with 8, and there ya go!

It sounds like a good solution - but what is ratiometrically, and what is VCC? Do you need to know a lot of electronics to wire a PIC?

Furthermore, can one PIC do DA conversion and quadrature emulation for

Thanks

Hmm, thanks for the link, power drain could be a problem. The unit driving this is a hagstrom ke72 (see

which has 5v, 0.5 mA per switch.