Analog joystick without potentiometers

Basically that is the way the MS Sidewinder works.

>>How can I build an analog joystick without potentiometers: >>I mean, something like a mouse, with optical components. a mouse is encoder based so, it in fact is digital. Same goes for any optical device that I can think of. To keep it analog you could use anything that varies resistance somewhere in the 100k-250k ohm range. Like a transducer type pressure switch. Or you could use an self powerd device as long as it's output was within the 0-5 volt range. It's too bad but, I can't think of anything better that good ol' pots for analog steering though. If you want to experiment, the standard IBM type pin assigns are as follows: 1.....+5 volts 2.....button one 3.....#1 axis "X" 4.....ground 5.....ground 6.....#1 axis "Y" 7.....button 2 8.....+5 volts 9.....+5 volts 10...button 3 11...#2 axis "X" 12...ground 13...#2 axis "Y" 14...button 4 15...+5 volts BTW there are good pots out there. They just don't put them on most joysticks/wheels.

> No you can't. > It's probably possible to build a joystick with this technique, but it > wouldn't be analog. A mouse isn't analog either. Well you could but it would be hard. you would have to have an encoder which will have DtoA's to simulate pots. It would be easier to examine the sidewinder or wingman serial protocols and encode the opticals wheels your self. Still non trivial. Unless there is a chip which does this. -- Bill Ryder Silicon Graphics New Zealand SGI V-Mail: 234 1456 Systems Engineer Ph: (+64 4) 494 6326 DISCLAIMER: Unless explicitly stated all opinions are mine not SGI's

Have you ever seen a DAC that gives resistence as output? I haven't, but if they exist I'd know a few nice things I'd like to do with them. // Johan

> > Well you could but it would be hard. you would have to have an encoder > > which will have DtoA's to simulate pots. > Have you ever seen a DAC that gives resistence as output? I haven't, but > if they exist I'd know a few nice things I'd like to do with them. Never came across a DAC that outputs resistance, but an alternative might be a digital potentiometer. Only problem there is the best resolution I've seen on digital potentiometers is 8 bits (256 discrete resistance steps) It might be resolution enough for sims, but then again it might not... Trips

> > Well you could but it would be hard. you would have to have an encoder > > which will have DtoA's to simulate pots. > Have you ever seen a DAC that gives resistence as output? I haven't, but > if they exist I'd know a few nice things I'd like to do with them. Nope but I found this: http://www.avtechpulse.com/papers/vres/index.html It says it is a 'active voltage controlled resistor' but I don't know if this would work. A DAC will output voltage though. Hmm.. Alternatively you could switch a resistor network (but that would be tedious and low res would't it?) -- Bill Ryder Silicon Graphics New Zealand SGI V-Mail: 234 1456 Systems Engineer Ph: (+64 4) 494 6326 DISCLAIMER: Unless explicitly stated all opinions are mine not SGI's

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> > > Well you could but it would be hard. you would have to have an encoder > > > which will have DtoA's to simulate pots. > > Have you ever seen a DAC that gives resistence as output? I haven't, but > > if they exist I'd know a few nice things I'd like to do with them. > Nope but I found this: > http://www.avtechpulse.com/papers/vres/index.html > It says it is a 'active voltage controlled resistor' but I don't know if > this would work. A DAC will output voltage though.

Here's another one - this one has 127 values in one chip: ftp://ftp.dalsemi.com/pub/datasheets/1666.ps From http://www.xs4all.nl/~ganswijk/chipdir/f/resist.htm -- Bill

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> > > Well you could but it would be hard. you would have to have an encoder > > > which will have DtoA's to simulate pots. > > Have you ever seen a DAC that gives resistence as output? I haven't, but > > if they exist I'd know a few nice things I'd like to do with them. > Never came across a DAC that outputs resistance, but an alternative > might be a digital potentiometer. Only problem there is the best > resolution I've seen on digital potentiometers is 8 bits (256 discrete > resistance steps) > It might be resolution enough for sims, but then again it might not...

I seem to recall the digital joystick have 8-bit resolution, and I also think it's loads better than the shaky analog ones we have now. "Shakes" of about 1/20 of the movement range are not uncommon (with bad pots you get 100% shakes (infinite resistance), but that's another issue) -- Anssi Lehtinen

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>>Have you ever seen a DAC that gives resistence as output? >I don't know exactly how a gameport measures resistance but I'd guess it's >putting the 5 volts across the pot and then measuring the voltage on the >swiper. You should be able to put a variable 0 - 5 volts on that pin and have >it work. >DISCLAIMER: Don't try this. If you decide to try this and fry your soundcard, >it was your decision to try it and I accept no responsibility. My advice is to >not try it. >But I bet it would work. ;)

And I bet it will not :-) Unfortunately, the PC port connects 5V to one end of the pot and uses the wiper (ie the variable resistance) to charge a capacitor in a monostable circuit. (the other end of the pot is not connected) Effectively, it is using a RC circuit's time constant to determine the resistance. Doing what you suggested will give a very non linear result. (that said, I've never tried this so someone could prove me wrong!) Toby -- Remove NOSPAM from address if replying by email.

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>> > > Well you could but it would be hard. you would have to have an encoder >> > > which will have DtoA's to simulate pots. >> > Have you ever seen a DAC that gives resistence as output? I haven't, but >> > if they exist I'd know a few nice things I'd like to do with them. >> Never came across a DAC that outputs resistance, but an alternative >> might be a digital potentiometer. Only problem there is the best >> resolution I've seen on digital potentiometers is 8 bits (256 discrete >> resistance steps) >> It might be resolution enough for sims, but then again it might not... >I seem to recall the digital joystick have 8-bit resolution, and I also >think it's loads better than the shaky analog ones we have now. "Shakes" >of about 1/20 of the movement range are not uncommon (with bad pots you >get 100% shakes (infinite resistance), but that's another issue)

I missed the start of this thread but.... 256 steps gives you almost 1 degree resolution. According to my calcs that is about 2mm movement of the edge of the wheel (assumes 25cm dia wheel). Might be OK but 10 bits would be better. As per another post (Bill Ryder?), you could build a discrete 10 bit dac using 10 resistors. D0----\/\/\/\------ output D1----\/\/\/\---| D2----\/\/\/\---| etc If you stick in a series diode for each resistor it makes the sums much easier! D0 resistor is 100R, D1 200R, D3 400R etc (Dn low, no affect. Dn high, resistance sums with other bits) Drive all this from something like a PIC microcontroller and you still have a couple of I/O pins for reading an optical encoder. (Guess what my first project will be when I get my PIC programmer working ;-) Toby -- Remove NOSPAM from address if replying by email.

for great info on our project go to www.sim-***s.nu please forgive the spelling

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> > > Well you could but it would be hard. you would have to have an encoder > > > which will have DtoA's to simulate pots. > > Have you ever seen a DAC that gives resistence as output? I haven't, but > > if they exist I'd know a few nice things I'd like to do with them. > Never came across a DAC that outputs resistance, but an alternative > might be a digital potentiometer. Only problem there is the best > resolution I've seen on digital potentiometers is 8 bits (256 discrete > resistance steps) > It might be resolution enough for sims, but then again it might not... > Trips

As a final bit on spme chips that will give you a digitally controlled 100ohm potentiometer: http://www.dalsemi.com/DocControl/PDFs/pdfindex.html These all look like 100Kohm, 256 position digitally controlled pots: DS1868 looks similar to other two. http://www.dalsemi.com/DocControl/PDFs/1868.pdf DS1803 low power, serial synchronous bus interface and addressable http://www.dalsemi.com/DocControl/PDFs/1803.pdf DS1267 two wire serial port settable http://www.dalsemi.com/DocControl/PDFs/1267.pdf mandatory disclaimer - I haven't had a close look at the datasheets to see if these are appropriate, I have glanced at them tho. You will need to check them out for yourself if you really want to do this. I must look at the PIC stuff too. ( http://www.microchip.com/ ) -- Bill Ryder Silicon Graphics New Zealand SGI V-Mail: 234 1456 Systems Engineer Ph: (+64 4) 494 6326 DISCLAIMER: Unless explicitly stated all opinions are mine not SGI's

> Here's a very nice page showing the particulars of a game port... > [link lost in import: /~wottenad/joyport2.txt] <Sarcasm on> I didn't check it out yet, but looking at the mediocre or even messed up game port support in most sims/games there may be more know-how in this little text file than there is in most game development departments... <Sarcasm off> l8er ronny -- Toys'R'Us '99: "So, would you like a hand gun with that action figure, kiddo?" |\ _,,,---,,_ I want to die like my Grandfather, ZZZzz /,`.-'`' -. ;-;;,_ in his sleep. |,4- ) )-,_. ,\ ( `'-' Not like the people in his car, '---''(_/--' `-'\_) screaming their heads off!

>Hello. >How can I build an analog joystick without potentiometers: >I mean, something like a mouse, with optical components. I am not sure how the mouse ranks as an analog device exactly... But a truly analog idea I've toyed with for a while would be using cheap and ubiquitos Hall effect devices and magnets to make a game controller. maybe there is one already. Seems like a cool solution- nothing to wear out, nothing to ever replace, at least on the electronic side. Turning the output in to a resistance to mate with standard joystick controllers might be tricky, but certainly solveable. I'd first try an FET. But a no-math (if sloppy and imprecise) alternative would be to use a photoresistor/LED pair and just bias the LED like you center a joystick. But alas, now that I am a programmer, don't have to breathe solder anymore, and the idea of electronic projects like that just about turn me to stone... Good luck, if you want to tackle it!