Capactiive touch on msp430g2553

Ayush Jain1

Other Parts Discussed in Thread: MSP430G2553

Hello guyz.. I am using msp430g2553 for capacitive touch application. I am facing a problem that capacitive buttons on P2.6 and P2.7 are not working properly. I need to adjust the threshold level regularly. There are 12 such capactive buttons but only these two buttons (connected on P2.6 and P2.7) are giving me trouble. Can someone please help me
?

over 11 years ago

0 Ilmars over 11 years ago

Guru 46710 points

Honestly I have no experience using particular two pins for pinosc, thou I know that they are special - check datasheet, "Pin-Oscillator Frequency", pay special attention to fact that p2.6 and p2.7 freq curves starts around 22pF of external capacitance. I guess that your "buttons" does not have enough capacitance to sustain stable oscillation. Other guess - freq change curve is no that steep as for P2.0 .. P2.5, in result you are getting less sensitivity

0 Ayush Jain1 over 11 years ago in reply to Ilmars

Prodigy 250 points

thx for the reply...your observation seems to be correct but what can be the solution to this problem...?

0 Ilmars over 11 years ago in reply to Ayush Jain1

Guru 46710 points

Try increasing sensor size for p2.6 and p2.7

0 Leo Bosch over 11 years ago

Guru 23000 points

Did you switch off the Low Frequency oscillator ‘BCSCTL3 |= LFXT1S_2;’ and disable his pins ‘P2SEL = 0;’?

0 Jens-Michael Gross over 11 years ago in reply to Leo Bosch

Guru 227245 points

Leo, for PINOSC, he has already cleared P2SEL and set P2SEL2.

However, the driver for XT1 might be still active (I’m not 100% confident with the port pin schematics regarding this). So LFXT1Sx should be set to VLOCLK, so ACLK doesn’t try to operate on XT1 and keep it active. Also set XCAPx to 0, so no load capacitance is added to the pins. (default is 6pF which significantly reduces sensitivity for PINOSC).

0 Leo Bosch over 11 years ago in reply to Jens-Michael Gross

Guru 23000 points

Jens-Michael Gross said:
Leo, for PINOSC, he has already cleared P2SEL and set P2SEL2.

How do you know that? I don’t see it here so to be sure, you never known.

Anyhow it’s silent here so problem seems to be solved.

0 Ayush Jain1 over 11 years ago in reply to Leo Bosch

Prodigy 250 points

Finally...problem has been solved... earlier gate count was 64 which was not giving me accurate result.. i have increased the gate count to 8192. The result is more accurate. P2,6 and P2.7 behaves differently from other pins and this can be verified using datasheet.

0 Ayush Jain1 over 11 years ago in reply to Ayush Jain1

Prodigy 250 points

thx a lot guyz for helping me out

0 Jens-Michael Gross over 11 years ago in reply to Leo Bosch

Guru 227245 points

Leo Bosch said:
Leo, for PINOSC, he has already cleared P2SEL and set P2SEL2.
How do you know that?[/quote]
Because otherwise the pin wouldn’t oscillate and he wouldn’t get any result, not just a wrong/insensitive/drifting result. :)

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Capactiive touch on msp430g2553