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I am trying to make a large scale resistive touch sensor with 4 FSRs, one for each corner of the rectangular sensor. The pressure that I'm going to be applying will be a moderately pressured finger press. I have heard that FSRs are mostly inaccurate as far as precise pressure goes.

For example, the Interlink 402 says in its datasheet that its accuracy is within 2% of its resistive value, and changes with time at a rate of 5% * log10( days ).

As far as tap sensitivity goes, the FSR seems decent, at 10% change after 10 million taps.

I'm wondering if with a passive load of 2kg, and a dynamic load of 1kg, would the 4 FSRs be sensitive enough to make a decent (512x512 (9-bit accuracy)), reliable resistive touch screen, or are other materials better for the cost? If I were to make this, what would my theoretical accuracy be?

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  • \$\begingroup\$ Link to the data sheet for the FSR would help. \$\endgroup\$ – Andy aka Jul 19 '17 at 17:34
  • \$\begingroup\$ @Andyaka boom. I was editing the question as you posted that comment. \$\endgroup\$ – tuskiomi Jul 19 '17 at 17:35
  • \$\begingroup\$ I think the data sheet provides you all the information you need. \$\endgroup\$ – Andy aka Jul 19 '17 at 17:53
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    \$\begingroup\$ 1kg load sounds like a hammer more than a finger. Note the sensitivity is given for one batch only and tolerance between batches must be compensated or calibrated and a matched lead-lag filter is my suggestion to compensate for these tolerances made to conjugate the fundamental spectrum of the dynamic load. ( fo=Hz toggle rate) ie. gain above DC null > fo = 10dB \$\endgroup\$ – Sunnyskyguy EE75 Jul 19 '17 at 19:55
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    \$\begingroup\$ It looks more like table banging sensor \$\endgroup\$ – Sunnyskyguy EE75 Jul 19 '17 at 21:28
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schematic

simulate this circuit – Schematic created using CircuitLab

300mV deflection at 2/3 FSR rating for load from 2/3 to 1 x FSR rating ?

enter image description here

Static load is probably quasi static, so dynamic touch will be problematic so DC tracking by AC amplification

Some problems with OEM specs at 10k expecting 2.5V at 50% FSR but only seeing 20% on left.

  • batch to batch variations may need a pot anyways.

Conclusion

  • possible if static load is true static.

  • undefined problems with this approach.

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  • \$\begingroup\$ Interesting. There is likely a better way then, huh? \$\endgroup\$ – tuskiomi Jul 19 '17 at 22:05
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    \$\begingroup\$ First specify all user interface dynamics in 4D, XYZ,t including resolution delta {XYZ,t} \$\endgroup\$ – Sunnyskyguy EE75 Jul 19 '17 at 22:27
  • \$\begingroup\$ Nono, i can't expect you to do any more for me; you've done much more than enough. nor anyone else. I'll go on to do as much as i can until i hit a block \$\endgroup\$ – tuskiomi Jul 19 '17 at 22:52
  • \$\begingroup\$ start with good interface specs not design. \$\endgroup\$ – Sunnyskyguy EE75 Jul 20 '17 at 0:27

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