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problem with touch key using ttp223

ultrasonic.1991

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Hi, I have designed a simple 4 pole touch key using ttp223 and modified it a couple of times. I encountered a problem using the final version of it. most of the time it works fine but sometimes when all the switches are on and I touch the third pole it doesn't respond to touching for 10 seconds and then it is back to normal and sometimes while I press the other poles the third pole has a false detection. the circuit has two parts that are connected to each other with pin headers. the power circuit and the touch key circuit that I attached the schematic and PCB for both of them. for the power, circuit p1 is the pin header for 220 to the 5-volt power supply. in the touch key circuit, p1 to p4 are connected to PCB pads. a light guide is placed over the LEDs and the PCB pad and a 4mm glass is placed on the light guide. D1 to D4 are 1n4148. i also attached a link to the datasheet of ttp223. can anyone tell me what is the problem?

ttt.png

dfvsrd.png

efse.png

ewdr3rw.png
https://datasheet.lcsc.com/szlcsc/TTP223-BA6_C80757.pdf
 

BradtheRad

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Is any input floating, not connected to a definite voltage? Is it the bare touch pad?

It probably needs some stratagem of electronic design to make it unaffected by ambient mains hum or static charge.

Ordinarily it might be a pull-up or pull-down resistor to a supply rail. However that makes it less sensitive to touch of a finger. Perhaps a 5 or 10 or 20 megohm resistor makes a reasonable tradeoff?
 

ultrasonic.1991

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thanks for your responce

Is any input floating, not connected to a definite voltage?
no, the inputs are not floating

Ordinarily it might be a pull-up or pull-down resistor to a supply rail. However, that makes it less sensitive to touch of a finger. Perhaps a 5 or 10 or 20 megohm resistor makes a reasonable tradeoff?
do you mean just one resistor parallel with 10 uf capacitor or one resistor parallel with each 1uf capacitor near the ttp223 ICs?
 

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ultrasonic.1991

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The link below uses a TTP223 where the schematic shows a capacitor from pin 3 to the ground. Your diagram doesn't have a capacitor or resistor in that position. Thus it appears to be a floating input that could cause it to respond with unexpected behavior.

www.electroschematics.com/ttp223-capacitive-touch-switch-circuit/
pins 3 is not floating it is connected to a PCB pad as you can see in the PCB image I sent. the capacitor from pin 3 to the ground is for reducing sensitivity but the device's sensitivity is ok so I don't need it and I tried using it and it makes everything worse.
 

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I wouldn't know if TTP223 is made to act differently, but if you touch a length of plain wire to the inputs of a logic gate, or op amp, or mosfet or bjt...
It becomes an antenna picking up 60 cycle hum. The output produces a 60 Hz square wave.

Sometimes this happens even if nothing touches the input terminal.

And if you touch your finger to the bare wire, and you carry a static charge, it causes the output to go sharply positive or negative (depending on whether you're positively or negatively charged).

It may continue this way for several seconds while the static discharges from your body. Then the output drifts back to an oscillating waveform.

These phenomena are on-again off-again, sometimes unpredictable. Sort of like the problem you report. And your inputs have a length of bare wire attached.
 

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