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QT113-D Touch Sensor — Parallax Forums

QT113-D Touch Sensor

wseibertwseibert Posts: 8
edited 2008-09-26 19:15 in General Discussion
I'm looking at using the QT113-D Touch Sensor for a application here and had some questions about it.

First, has anyone here used this sensor in a application before?

Would anyone be able to tell me if there is a limit on how long the sensor wire can be?· I'm looking at having the sensor wire be able 2-3 feet from the actual board/chip.· Would this be ok, or is it going to affect the sensor ablity to function correctly?

thanks for any/all input· =)

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2008-09-25 16:45
    Hello,

    The datasheet for the part goes into more detail on this sort of thing. I would check there first and then follow-up on this thread if you have more questions. I myself haven’t used it that far from the sense plate, so it may be something you have to test.

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    Chris Savage
    Parallax Engineering
  • wseibertwseibert Posts: 8
    edited 2008-09-25 16:53
    Yeah, i looked over the data sheet and it doesn't give that much information on it (sensing distance in wire). I'm thinking about getting one of this and testing with it (my application will require 5 of these sensors).

    I was hoping someone here already had a chance to work with this IC and would be able to give us some insite on how well it works =)

    Thanks!
  • T ChapT Chap Posts: 4,249
    edited 2008-09-25 17:15
    I have used several feet before no problem, but remember, the wire is also touch sensitive.

    Keep the wire clear of grounds as well, it is suggested that the wire not be shielded, or have the PCB traces be ground poured near the traces from the chip to the sensor.

    I don't use that exact model, but the technology is great between all their chips. Adjust(change) the cap to set the sensitivity.
  • wseibertwseibert Posts: 8
    edited 2008-09-25 17:32
    Thanks Originator!

    What about having multiple sensor wires running together (like in a cat 5 cable)? Would/Should the cables be shielded then?

    Thank You
  • T ChapT Chap Posts: 4,249
    edited 2008-09-25 19:16
    The lines to sensors should not be close to gnd as it can affect sensitivity. Of course you should do some trial and error, see what works. It may very well be OK in shielded cable, I have never tried shielding the wires though.

    I am certain that by adjusting the cap value, you will find some method that works just fine.
  • wseibertwseibert Posts: 8
    edited 2008-09-26 16:10
    I'll give that a try.... I'll have to get one of the chips (ordered first) and test it out. Once i get some test data, i'll let you know.

    (looking at the datasheet for the chip, has a sample circuit)
    In adjusting the cap value, would i be able to adjust the resistor as well (to adjust the sensor)?

    Would a pot (in place of the resistor) work?

    Thoughts?

    Thanks!
  • T ChapT Chap Posts: 4,249
    edited 2008-09-26 17:24
    The resistor stays the same. You can only adjust sensitivity by changing the cap value. A smaller value (10nF is more sensitive than 39nF) etc. You set the cap to accomplish the amount of proximity or touch pressure required to trip the output. Depending on the size and thickness of the sensor, you can achieve non-touch triggering, meaning you get within so many inches and it trips. With a higher value cap, more pressure is required to trigger it on touch. If using a multi channel version, there is a Adjacent Key Suppression mode that can be used to reject false triggers, it makes the chip choose only one sensor if there are several (adjacent) sensors that are getting picked up at once. In this case, you can actually drag your fingers across boundaries of sensors, but the chip chooses the strongest signal to output a high. If using multiple sensors, you may consider this mode.
  • wseibertwseibert Posts: 8
    edited 2008-09-26 17:57
    Ah, ok

    Maybe i'll look into a adjustable cap for the circuit then...

    I'll also look into the Adjacent Key Suppression mode as well. The sensors will be right next to each other (in a row), and i'll have to make sure i don't get any false 'touch'es from the neighbor sensors.

    I'll work on the circuit design this weekend and post the design if i get it done... after that will be making it on a breadboard and testing it out!

    Cool

    Thanks!
  • T ChapT Chap Posts: 4,249
    edited 2008-09-26 19:15
    An adjustable cap may work, I have never experimented with one, the ranges you need are 10nF to 50nF. Maybe it would be easier to switch caps in and out in parallel, but honestly I just always solder in a value, test it, unsolder it and solder in another until it feels tight, then you are set. You should study the Qprox website, there is a lot of info there, tips, etc.
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