PSoC™ 4 Forum Discussions

[wangjiazheng]

Hi,community

  I want to design a simple capacitive touch button with only a metal sheet as the sensor, which is used to control the switch of led, Relevant examples are how to design on a PCB board,but i need a button independent of the PCB. Do you have relevant suggestions or examples.

  thanks

[PandaS · Accepted solution]

Hi @wangjiazheng ,

If I understood correct, you want to develop a prototype. You can start with a copper strip and cut it in a shape of the sensor you want. Connect that copper piece with one of the pins. This should be a good start point. It is good for prototyping, but for deployment purpose we should go for a PCB design.

Warm regards

Sobhit

[Vison_Zhang]

Sobhit provides a very clear diagram, but two attentions:

1. The wire connects sensor pin and sensor plate should be as thin as possible and fixed (e.g. taped to a non-metallic surface of the structure).

2. Placing a 560ohm~2k series resistor near sensor pin. 

[wangjiazheng]

Hi PandaS,Hi Vison

        Thanks for your reply,  I still have a few questions. If you need to improve the ability of electromagnetic interference, whether you need a grounding grid around, if necessary, how to layout, or other means of shielding electromagnetic interference. I want to make a touch switch for the interior roof light to replace the mechanical switch. Do you have any good test methods you can suggest for EMC testing or how to test the stability of the touch switch? Can I use smartsense in a real project, or do I need to set my own parameters to as high a threshold as possible to avoid false triggers?

[wangjiazheng]

Hi PandaS,Hi Vison

        Thanks for your reply,  I still have a few questions. If you need to improve the ability of electromagnetic interference, whether you need a grounding grid around, if necessary, how to layout, or other means of shielding electromagnetic interference. I want to make a touch switch for the interior roof light to replace the mechanical switch. Do you have any good test methods you can suggest for EMC testing or how to test the stability of the touch switch? Can I use smartsense in a real project, or do I need to set my own parameters to as high a threshold as possible to avoid false triggers?

[PandaS]

Hi @wangjiazheng ,

For EMI protection: Ground hatch is important, and for that we need to design PCB. Even after that, I have seen customers face issue while designing systems with AC loads. Usually the Relay may generate a transmitted Voltage surge. To prevent that, I would recommend having a optocoupler as Digital Isolator in between the relay and sensor output. Sometimes, these surges hang the PSoC. It is has nothing to do with CapSense but with GPIO output pin driving the relay.

For the Conducted Emissions we can use a optocoupler to isolate the relay from the PSoC optically. Refer to the circuit below:

I would recommend having the optocoupler before the ULN2803 Driver(Buffer).

Yes, you can use SmartSense for your project, it is just that the Manual tuning would have bit faster response and more suited for your project.

Warm regards,

Sobhit