12 Jun
2009
12 Jun
'09
5:34 a.m.
I'm working on reproducing a pair of Cromemco JS-1
joysticks to display (and let the public play with) at
VCF East in September. The one thing I'm missing is a
small, panel mount joystick assembly with 5k Ohm pots.
I have done a fair amount of googling. New assemblies
cost anywhere from $60 to $200 each (I need 2). This
is more than I want to spend on this project. I've
already spent more on the Hammond enclosures than I
really wanted to.
It was suggested to me that a used radio control model
transmitter might be just the ticket. Googling shows
that at least some use 5k pots and they go fairly cheap
on ebay. I don't want to end up with a collection of
RC transmitters (and end up spending as much as I would
have on new joystick assemblies) so my questions for
the group are:
1) Anybody have a 2 stick transmitter with known 5k pots
they want to sell?
2) If you have an RC transmitter you want to keep, could
you open it up and check the pots so I can have a
list of models to keep an eye for on ebay?
3) An finally, of course, anybody have a couple of panel
mount joystick assemblies with 5k pots they want to
sell cheap or work a trade for?
Thanks,
Bill Sudbrink
12 Jun
12 Jun
1:51 p.m.
I'm working on reproducing a pair of Cromemco JS-1
joysticks to display (and let the public play with) at
VCF East in September. The one thing I'm missing is a
small, panel mount joystick assembly with 5k Ohm pots.
Not being a Cromemcop person, I don't have scheamtics..
How are the pots used? As potential dividers (one end to ground, other
end to a power line, slider to an analogue input). Or as variable
resistors (only 2 wires brought back from each pot, a commen way to use
them like that was to use them in an RC timing network possibly round a
555 or similar (c.f. Apple ][, IBM PC, etc).
If the former, then the value of the pot doesn't matter too much (I would
think 10k would be fine, for example). If the latter, you might be able
to use other values of pot by changing the timing capacitor or whatever.
If it is used as a potential divider, I have a circuit to use a normal PC
jouystick on such an input ('normal PC joystick meaning one of the old
analouge ones that plugs into a DA15 socket on a games controller card).
I can dig it out if you think it would be useful. IIRC it's just a
multiple op-amp chip, a couple of transistors, and some R's and C's. I
designed it to use PC joysticks on a Vectrex.
-tony
5:41 p.m.
Tony Duell wrote:
Not being a Cromemcop person, I don't have
scheamtics..
There's a PDF on Harte's S-100 site.
How are the pots used?
+12V on one end, -12V on the other and the center tap goes
back to the A to D card. The test procedure specifies +2V
and -2V at the full deflection of the stick.
6:04 p.m.
Bill Sudbrink wrote:
+12V on one end, -12V on the other and the center tap
goes
back to the A to D card. The test procedure specifies +2V
and -2V at the full deflection of the stick.
Wired like that, the exact value of the potentiometers doesn't matter.
If it's easier to find joysticks with 10K potentiometers, they should
work. Too low a resistance will draw too much current (possibly
exceeding current or power ratings of the potentiometer), and too high a
resistance (relative to input impedance of the ADC) things won't work
properly, though no damage will result.
Eric
6:31 p.m.
Eric Smith wrote:
Wired like that, the exact value of the potentiometers
doesn't matter.
If it's easier to find joysticks with 10K potentiometers, they should
work. Too low a resistance will draw too much current (possibly
exceeding current or power ratings of the potentiometer), and too high a
resistance (relative to input impedance of the ADC) things won't work
properly, though no damage will result.
Well, PC and Apple joysticks (easy to find) are between 100k
and 150k Ohms... 20 to 30 times the desired values. Some RC
transmitters may have 10k pots. My only knowledge of RC
transmitter pot values is a couple of web pages about retro-
fitting a board with a PIC on it into old analog transmitters
to get digital control of the model. The pages say things
like "If you have 5k pots, install this resistor and cap.
If you have 10k pots, install this other resistor and cap."
etc...
6:41 p.m.
Bill Sudbrink wrote:
Well, PC and Apple joysticks (easy to find) are
between 100k
and 150k Ohms... 20 to 30 times the desired values. Some RC
transmitters may have 10k pots. My only knowledge of RC
transmitter pot values is a couple of web pages about retro-
fitting a board with a PIC on it into old analog transmitters
to get digital control of the model. The pages say things
like "If you have 5k pots, install this resistor and cap.
If you have 10k pots, install this other resistor and cap."
etc...
I'm not certain, but I think 100K or 150K will probably work OK, and it
won't damage the ADC to try it.
I'm not completely certain about PC joysticks, but joysticks made for
the Apple II are wired with electrical connections to the wiper and one
end only. The other end may be open, or connected to the wiper.
Eric
13 Jun
13 Jun
4:18 a.m.
On Fri, 2009-06-12 at 21:31 -0400, Bill Sudbrink wrote:
Eric Smith wrote:
Close enough, for this. It's just a potential divider. Have you tried
it?
Wired like that, the exact value of the
potentiometers doesn't matter.
If it's easier to find joysticks with 10K potentiometers, they should
work. Too low a resistance will draw too much current (possibly
exceeding current or power ratings of the potentiometer), and too high a
resistance (relative to input impedance of the ADC) things won't work
properly, though no damage will result.
Well, PC and Apple joysticks (easy to find) are between 100k
and 150k Ohms... 20 to 30 times the desired values. Some RC transmitters may have 10k pots. My only knowledge of
RC
transmitter pot values is a couple of web pages about retro-
fitting a board with a PIC on it into old analog transmitters
to get digital control of the model. The pages say things
like "If you have 5k pots, install this resistor and cap.
If you have 10k pots, install this other resistor and cap."
etc..
That's because it uses the RC time constant to measure the value of the
pot. It doesn't care about the voltage. You set the pin to output low
so you discharge the cap and then set it to be an input and time how
long it takes to go high again. The higher the pot value, the longer
the time.
Gordon
4:36 a.m.
Gordon JC Pearce wrote:
That's because it uses the RC time constant to
measure the value of the
pot. It doesn't care about the voltage. You set the pin to output low
so you discharge the cap and then set it to be an input and time how
long it takes to go high again. The higher the pot value, the longer
the time.
The Cromemco D+7A card does use a ADC circuit composed of a DAC(1408),
SAR, and Opamp Comparator. It does care about the voltage. I have one of
the Cromemco JS-1 joysticks ( http://tinyurl.com/nqcbkm ) and plan on
duplicating this circuit too to make it compatible with existing
software. That method you described had been used on other micro's, such
as the Apple II and TRS80 mod.I to keep parts cost low.
=Dan
[ = http://www2.applegate.org/~ragooman/ ]
12 Jun
12 Jun
6:22 p.m.
Bill Sudbrink wrote:
+12V on one end, -12V on the other and the center tap
goes
back to the A to D card. The test procedure specifies +2V
and -2V at the full deflection of the stick.
Bill,
After looking at my copy of the D+7A schematic, you probably could get
away with using joysticks pots which are higher in value, say 10Kohms.
Looking at the 4051 mux datasheet, the input current required is
minuscule, measured in the microamps, which should make it still
possible to use joysticks with a little more resistance.
=Dan
13 Jun
13 Jun
12:24 p.m.
Tony Duell wrote:
Assuming there are no typos there, this sounds like one of those joystick
mechanisms that only uses the middle bit of the rotation of a normal
potentiomete (hence the swing to +/-2V, not +/-12V). A lot of joysticks
I've seen have special pots with a shortend resistive track so you get an
output swing essentially the same as the supply voltage -- this is not
what you want here.
Howeer, assuming the input inmpedance of the ADC card is fairly high, the
actual value of the potentiometer resistance is not likely to be critical.
If you have _any_ analogue joystick, you can probably convert it to work.
If it's a 3-terminal potentiometer type, fiddle the voltages applied to
the ends of the track to get the right swing on the slider (e.g. if the
slider goes from one end of the track to the other, you could supply it
Not being a Cromemcop person, I don't have
scheamtics..
There's a PDF on Harte's S-100 site.
How are the pots used?
+12V on one end, -12V on the other and the center tap goes
back to the A to D card. The test procedure specifies +2V
and -2V at the full deflection of the stick. from +/-2V, and have a +/-2V output). If necessary (if
the potentiometer
resistance is too high), you can buffer the output from the wiper
using
an op-amp wired as a unity gain buffer.
If you have a 2-terminal joystick (a variable resistor), like most old PC
joysticks, it's a bit more work. WHat I did wa make a current sink
(op-amp + transistor + R's) and connect the variable resistor between the
top of that and +5V (I kept it going to +5V, as in a PC, so that any
autofire circuits in the joystick would still work). Then the voltage
drop across the variable reisstance is proportional to the resistance
(constant current, remember). I tapped that off, and used an op-amp or
two to get the right output swing and offset.
-tony
23 Jun
23 Jun
4:23 p.m.
Just a follow-up in case any future reader wants
information. I took a chance and bought an old
Futaba FP-T5FN radio control transmitter, offered
on ebay. It cost $26 plus $10 shipping. I consider
myself triply lucky:
1) The unit had not been used in many years and
the internal battery had leaked all over the
main circuit board, completely ruining it.
This considerably eases my conscience over
tearing up the unit and only using the sticks.
2) The joysticks have 5k pots as required and,
other than a very light coat of fuzz on the pot
cans, were unaffected by the leak and operate
perfectly.
3) As a bonus, the joysticks' physical appearance
very closely resembles those originally used
by Cromemco.
Bill Sudbrink
5660
days inactive
5671
days old
10 comments
5 participants
participants (5)
-
ard＠p850ug1.demon.co.uk -
eric＠brouhaha.com -
gordonjcp＠gjcp.net -
ragooman＠comcast.net -
wh.sudbrink＠verizon.net