Analog in on OI: Heads Up!

[Astronouth7303]

Heads up: The OI will output 127 for what it perseves as infinate resistance. I'm not sure of the exact threshold, but my theory is that when volts <= 0.1, it outputs 127. But noise (flickers between 0 and 127) goes until about 0.110 or 0.115.

So if, as an example, you wire a potentiometer to p4_aux, when the pot. is all the way down, p4_aux=127. when it's a little higher, p4_aux=0.

also, 127 appears in it's "normal" position (midway 'round). So you can't just put in an if statement.

I hear this is by design. So watch out!

[Dave Flowerday]

Originally Posted by Astronouth7303

Heads up: The OI will output 127 for what it perseves as infinate resistance. I'm not sure of the exact threshold, but my theory is that when volts <= 0.1, it outputs 127. But noise (flickers between 0 and 127) goes until about 0.110 or 0.115.

So if, as an example, you wire a potentiometer to p4_aux, when the pot. is all the way down, p4_aux=127. when it's a little higher, p4_aux=0.

also, 127 appears in it's "normal" position (midway 'round). So you can't just put in an if statement.

I hear this is by design. So watch out!

This is by design (so that when you unplug your joystick when the robot is still running, it doesn't start running it's motors full speed backwards).

If you're wiring a pot such that it can pull the analog input on the OI down to less than 0.05 volts (the spec which is stated in the OI documentation from IFI), then that means you have ground connected to the pot. Check the OI reference - this is not the correct way to wire a pot to the OI.

Besides, you already asked this question and I already answered it. Why are you posting this same thing twice?

[Astronouth7303]

A sure sign your posting too much: You forget what you posted already and then post the same thing again.

But thanks on the wiring thing, I'll check that. but our solder boy won't be happy.

Good call, though. I should remember these things.

[Biff]

Originally Posted by Astronouth7303

Heads up: The OI will output 127 for what it perseves as infinate resistance. I'm not sure of the exact threshold, but my theory is that when volts <= 0.1, it outputs 127. But noise (flickers between 0 and 127) goes until about 0.110 or 0.115.

So if, as an example, you wire a potentiometer to p4_aux, when the pot. is all the way down, p4_aux=127. when it's a little higher, p4_aux=0.

also, 127 appears in it's "normal" position (midway 'round). So you can't just put in an if statement.

I hear this is by design. So watch out!

This is designed this way, I asked the people at Innovation First they said when there is 0 volts on the input, the default is 127. We tested ours and voltage level of 0.3 or so will get you 0 for that input less than that voltage and results vary. We are using 15K pots with 560 ohms feeding the ground side of two pots. Ie 7.5 k in series with the 560. Hope this helps.

[Dave Flowerday]

Originally Posted by Biff

We are using 15K pots with 560 ohms feeding the ground side of two pots. Ie 7.5 k in series with the 560. Hope this helps.

You're only allowed to use 100K ohm pots on the OI inputs. Check the OI Reference Guide page 5. There's a good reason for this, and it's related to the the fact that there's a pulldown internally inside the OI (to force the 127 condition when the joystick is unplugged).

It sounds like your setup looks like this:

 
         15k                   15k
+5v ---/\/\/\/\------+-------/\/\/\/\----- +5v
                    |
                    \
                    /
                    \ 560 ohm
                    /
                    \
                    |
                  Gnd

If this is the case, check the wiring diagram again on Page 5. This isn't the right way to connect to the analog inputs.

[Biff]

Originally Posted by Dave Flowerday

You're only allowed to use 100K ohm pots on the OI inputs. Check the OI Reference Guide page 5. There's a good reason for this, and it's related to the the fact that there's a pulldown internally inside the OI (to force the 127 condition when the joystick is unplugged).

It sounds like your setup looks like this:

 
         15k                   15k
+5v ---/\/\/\/\------+-------/\/\/\/\----- +5v
                    |
                    \
                    /
                    \ 560 ohm
                    /
                    \
                    |
                  Gnd

If this is the case, check the wiring diagram again on Page 5. This isn't the right way to connect to the analog inputs.

Thanks it's a case of Re RTM