Analog Capacitive Question

 
#1

I am thinking about adding analog capacitive wires for my InMoov but have a questions. All of my V4's are in use on the inmoov right now so I dont have one to try this with or I would.

In order for the analog signal to increase or decrease when a wire is touched, I assume that I have to provide current (+ and/or -) to the pad that I will be incorporating along with the signal wire. Is this an accurate statement or do I just need the signal wire?

Thanks
David

#2

@David.

I don't know if the information here will be of any use to you. The sensors described here are similar to the flex sensors I used which just use the signal and ground pins on an analog port.

#3

Are you needing a touch sensor or an "amount of force" sensor?

#4

touch sensor

#5

If the touch sensor provides resistance when touched, then you can read this resistance value right from the analog port... no need for an external source of power... @Bob should comment, I believe he made some simple ones for his inMoov...

#6

More questions:
Does it have to be an analog signal or would a digital touch switch signal work for what you need?
If it can be digital, would you want it to just trigger a digital input or would you need it to pull in a relay?

#7

Ideally, I would just run the wire to a small hole in the finger. At that point any resistance to a conductive object (such as a person) should be able to be measured.

The other option is to use foam from one of the EZ-Robots boxes that I have and run ground and the signal cable through the fingers to some copper strips, which would then allow me to measure pressure more than just touch.

I think I am just going for touch but don't have much room at all to put in switches. these finger tips are pretty tight.

#8

@David... I think you can do that with a pullup or pulldown resistor (depending on how you wire it) ... as an experiment, If you take 2 wires... one on the analog signal pin and one on the ground pin... Now squeeze them between your fingers without letting them touch each other... You will see the analog value rise and fall depending on how hard your squeeze... what you are seeing is a change in resistance value...

#9

I know @bob made some cheap home made touch sensors... I am not quite sure how he made them but maybe he'll chime in and let us know...

#10

Yep, the antistatic foam that is in the EZ-Robot boxes will act as a resistor. As the foam is compressed it becomes less resistive and conducts more electricity. That is the theory anyway. I have to find something to do with all of these analog ports and this seems like as good of a thing as anything at this point. I can have 8 ports per hand right now. The thought is that 5 of these would be in the fingers and a few of them in the palm (thinking thumb, palm and pinky joints in the hand). This should allow me to know how tight something is being held. There is a ground run to the wrist just outside of the rotational servo.

Do the ground and signal pins have to run off of the EZ-B or is a common ground good enough? Lots of testing to do on this.

As for other points for contact sensing, I have 16 more analog ports to use. I figure shoulders, and head would be a good place to add some copper for touch sensing. I may do something in the stomach, not sure.