Potentiometer 5 or 6 detents

[Travis Covington]

We want to use it to select autonomous modes. Anything under 12 detents will work. We are just having trouble actually finding any. I know some of you have used these... a part number would be great! Thanks!

[Adam Shapiro]

Originally Posted by Travis Covington

We want to use it to select autonomous modes. Anything under 12 detents will work. We are just having trouble actually finding any. I know some of you have used these... a part number would be great! Thanks!

It seems like it may be rather hard to find such a pot. You may want to just use a standard pot, however, and program the robot to respond to ranges of analog input rather than a specific value. So that you could turn it approximately to the correct program, rather than the specific value.

If you don't have too many autonomous programs you could use a series of switches as a binary selector. You'd only need 5 bits (5 inputs out of the 4 ports) to cover the 12 modes you seem to need and more.

[Travis Covington]

We found one on digikey, but it doesnt have a shaft (to accept a knob) and is rather small at only 16mm wide.

Thanks for the help, we will keep looking. I am sure they are out there.

[Kris Verdeyen]

If you look around page 1433 of the digikey catalog (which I totally knew off the top of my head), you'll find a type of switch that might be better for your application. It's called a rotary switch, and they come in all kinds of configurations, including SP6T. You can solder a bunch of resistors around the terminals, and it will behave exactly how you described, and can look like a pot to the OI or RC.

[Alan Anderson]

Yeah, what Kris said. The TechnoKats used a many-position rotary switch with resistors between each contact as an automode selector on the KatsKlaw OI in 2004.

[KenWittlief]

forgive my ignorance of this years OI, is the red LED display still able to display user selected numbers?

set your code to read a joystick or pushbutton input - everytime you push the button increment a counter, and display it on the OI LED numeric output - that is your autom mode number

you could have up to 256 different auton modes that way.

[Travis Covington]

The rotary switch seems like a good solution, if it does in fact have solid feeling stops, so we could easily differentiate between the 6 positions.

The only problem is, I would be the one wiring it up and have practically zero electronics knowledge and would need some help selecting resistors and wiring it up to specific pins on the switch and the RC. If you guys could help me out there, It would be HUGELY appreciated.

[Adam Shapiro]

Originally Posted by Travis Covington

The rotary switch seems like a good solution, if it does in fact have solid feeling stops, so we could easily differentiate between the 6 positions.

The only problem is, I would be the one wiring it up and have practically zero electronics knowledge and would need some help selecting resistors and wiring it up to specific pins on the switch and the RC. If you guys could help me out there, It would be HUGELY appreciated.

The idea here isn't as much the actual resistance as the concept. The current through the circuit I is defined as I=V/Rtotal where Rtotal is the sum of the two resistors: the initial one connecting from 5V to the common lead, and the secondary resistor from the switch to ground. Then the voltage measured at the common lead can be calculated as V=IRswitch (the resistance from the switch to ground). The actual R value will cancel out.

----- Rc ----- Rswitch <--the dashes are just spacers here...
5V--^v^v--|--^v^v--gnd
________Input
Rc=R, Rswitch=#R
I=(5V)/(Rc+Rswitch)
Vinput=I(Rswitch)=(5V)(#R)/(R+#R)=(5V)(#)/(1+#)

Hope this helps.

[Travis Covington]

Originally Posted by Adam Shapiro

Hope this helps.

Sort of... In reality, I still have no idea where to start. I am an ME/MFE with very little electronics experience... so please bear with me.

[Adam Shapiro]

Originally Posted by Travis Covington

Sort of... In reality, I still have no idea where to start. I am an ME/MFE with very little electronics experience... so please bear with me.

Heh, not a problem. You should probably choose some value of R in the 10000s to protect the input (I believe).

EDIT: It seems the OI manual suggests 100k ohms for a value. This seems resonable as it will only allow for a very small amount of current between 5V and gnd (I=V/R=5/(100000)=50uA). This is for safety as well as to prevent against large flows of current when using the OI. Don't forget the OI has its own built in fuses to protect itself, but you still want to be careful.

[Travis Covington]

My plan was to mount it on the RC.

[Adam Shapiro]

Originally Posted by Travis Covington

My plan was to mount it on the RC.

The RC has the same thing going for it. The only thing I would be concerned with however is that using a rig like this might be a bit cumbersome. Personally I'd use a 100k ohm potentiometer, rather than a rotary switch, and just set specific ranges as certain programs. This could also be reprogrammed to allow for smaller ranges -> more programs. That's up to you though. The math/physics behind the voltage divider idea would stay the same though, you'd just hook it to an analog input on the RC rather than one on the OI.

[Al Skierkiewicz]

There are pots that exist that have detents built in but there are generally used for volume controls (are log taper, 10K) and have 10-12 detent positions. A better solution is to pick up a six position switch at Radio Shack.
http://www.radioshack.com/search/ind...ar y%20switch

This switch is easily modified to become a twelve position switch by bending one of the stopper tabs out of the way and cutting one of the contact springs. Wire 9.1K ohm resistors from each terminal to the one next to it to form a series string. When you are done, you have a stepped 100K pot. Wire as you would any pot to an analog input on the OI and then set your programmers to work. RS has some nice shiny knobs as well. If you would like to see one in action, stop by our pit in Atlanta.

[Travis Covington]

Are you saying to use the 9.1k resistors if I wanted to have 12 positions? Would I still use the 15k resistors if I were to only use the 6 positions?

[Alan Anderson]

Originally Posted by Adam Shapiro

The idea here isn't as much the actual resistance as the concept...

If the switch is going on the OI, the actual resistance is rather important. The OI analog inputs want to see a variable resistance between ~2k and 100k to give the full range of values.

For a six-position rotary switch, I'd use six 15k resistors wired like this:

+5 <----/\/\/--*--/\/\/--*--/\/\/--*--/\/\/--*--/\/\/--*--/\/\/--*
                         ^
 OI                      |
analog input <-----------'

The * characters represent the six positions of the rotary switch, and the ^ is the common connection.

What you'll get from this is the equivalent of a joystick with six discrete resistance values: 15k, 30k, 45k, 60k, 75k, and 90k. You should use a dashboard program to determine what the actual numbers end up being, and choose appropriate ranges in the software to decide which of the six positions is chosen.