problem with touch key using ttp223

Go To Last Post
6 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

hi, I designed a simple 4 pole touch key using ttp223 IC. I encountered two problems when using it. sometimes when I touch a key, another random key switches. and sometimes when I reset power, a key switches to a condition and never switches back after touching. I attached the 1 pole circuit and the power circuit. about the component with the picture of LED I should say that its a PCB pad connected to the third pin of ttp223 and two back to back LEDs are placed under it and a light guide which distributes light is placed over the LEDs. and a 4 mm glass is placed over the light guides. in the power circuit, I used a 220 to 5v small SMPS. the relays are 5v dc and 120v ac.
what do you think the problem is?.
I found that there is something called snubber circuit which is a resistor series with a capacitor parallel with the contact pins of relay for suppressing excessive noise and also there is an option of optocoupler for isolation and suppressing noise. are these useful in my case?
thanks in advance

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

salar1991 wrote:
I designed a simple 4 pole touch key using ttp223 IC.

can you provide a link to the datasheet, I've never heard of this chip?   

Is it U2 in the schematic above, speaking of which, why not DRAW the circuit rather then show a bunch of parts scattered all over with net labels, there are not that many parts above, so draw all the connections.

Schematics flow from left to right, so inputs on the left, outputs on the right, VCC on top, GND's on the bottom.

Logic chips need bypass caps(100nf) connected from vcc to gnd, placed as close to the chip as possible.

Voltage regulators also need caps on input and outputs, what is U1, show link to datasheet as well.

Board layout is critical to success when using low voltage (cap touch!) and anything using relays to switch High Voltage AC.   Please show a clear photo of your circuit board.

Relays usually need back biased diodes across the coil to suppress the voltage spike when the magnetic field collapses when power is removed (de-energizing the coil).

Jim

 

 

FF = PI > S.E.T

 

Last Edited: Thu. Aug 27, 2020 - 03:45 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

ki0bk wrote:

salar1991 wrote:
I designed a simple 4 pole touch key using ttp223 IC.

can you provide a link to the datasheet, I've never heard of this chip?   

Is it U2 in the schematic above, speaking of which, why not DRAW the circuit rather then show a bunch of parts scattered all over with net labels, there are not that many parts above, so draw all the connections.

Schematics flow from left to right, so inputs on the left, outputs on the right, VCC on top, GND's on the bottom.

Logic chips need bypass caps(100nf) connected from vcc to gnd, placed as close to the chip as possible.

Voltage regulators also need caps on input and outputs, what is U1, show link to datasheet as well.

Board layout is critical to success when using low voltage (cap touch!) and anything using relays to switch High Voltage AC.   Please show a clear photo of your circuit board.

Relays usually need back biased diodes across the coil to suppress the voltage spike when the magnetic field collapses when power is removed (de-energizing the coil).

Jim

 

u2 is ttp223 as you guessed and u1 is a voltage regulator (AMS1117) and about the diodes, I already used them in my circuit you just didn't see them. they are on the left side of the schematic.  I attached the datasheet of ttp223 

http://www.mediafire.com/file/a149h9dm8wbakf0/TTP223-BA6_C80757.pdf/file

and here is the layout pics of my circuit that has 2 parts power circuit and the main circuit

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 1

salar1991 wrote:
I already used them in my circuit you just didn't see them.

My point exactly, and neither will you in a few months when you return to this project, and why I said...

ki0bk wrote:
DRAW the circuit rather then show a bunch of parts scattered all over with net labels

that only leads to errors as things are TOO easily missed!

 

Your layout has many problems, a few include,  not enough spacing between High and Low voltage components. Arc flash can happen from HV line traces to low voltage traces, here in the US there are UL regulations that specify the minimum PCB trace gap size for HV circuits(R3 to K4 coil, phase to common of K3 is too thin).  Your diodes are some distance away from and using long narrow traces (think inductance) from the relay coils.  Feed thru's should not be placed in pads (D2).

Like you schematic, your pcb layout does not look like much thought was used before beginning layout, rather just hook up the pins. 

 

Start again, and draw a schematic, and be aware of high voltage requirements and rearrange your relays to keep HV traces wide and well spaced from each other and away from the LV circuit traces.

 

I recently had to replace the control board in my home Electric Range, upon inspection of why the board failed, I found charred bodies of ants between the HV and LV(coils) of the relays that powered the heating elements.   There was no conformal coating of the pcb and HV - LV clearances were too small, a line of ants walking across the board allowed the HV to jump to the LV circuits and kill the board.

Strange things like that happen in the real world, as engineers, we must anticipate unlikely things like that can, and will happen. 

Good luck with your project.

 

Jim

 

 

 

FF = PI > S.E.T

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

ki0bk wrote:

salar1991 wrote:
I already used them in my circuit you just didn't see them.

My point exactly, and neither will you in a few months when you return to this project, and why I said...

ki0bk wrote:
DRAW the circuit rather then show a bunch of parts scattered all over with net labels

that only leads to errors as things are TOO easily missed!

 

Your layout has many problems, a few include,  not enough spacing between High and Low voltage components. Arc flash can happen from HV line traces to low voltage traces, here in the US there are UL regulations that specify the minimum PCB trace gap size for HV circuits(R3 to K4 coil, phase to common of K3 is too thin).  Your diodes are some distance away from and using long narrow traces (think inductance) from the relay coils.  Feed thru's should not be placed in pads (D2).

Like you schematic, your pcb layout does not look like much thought was used before beginning layout, rather just hook up the pins. 

 

Start again, and draw a schematic, and be aware of high voltage requirements and rearrange your relays to keep HV traces wide and well spaced from each other and away from the LV circuit traces.

 

I recently had to replace the control board in my home Electric Range, upon inspection of why the board failed, I found charred bodies of ants between the HV and LV(coils) of the relays that powered the heating elements.   There was no conformal coating of the pcb and HV - LV clearances were too small, a line of ants walking across the board allowed the HV to jump to the LV circuits and kill the board.

Strange things like that happen in the real world, as engineers, we must anticipate unlikely things like that can, and will happen. 

Good luck with your project.

 

Jim

 

 

thanks, I'll try to make the diodes closer to relays as you said but how much should the space between high voltage and low voltage traces be?

  and adding polygon and via stitching to the second circuit(power circuit) is necessary? what about the snubber circuit and optocoupler? are they useful in my case? 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

you must use snubber circulate on relay