EMI issue with household electrical equipment

Thread Starter

nguyendai

Joined Mar 22, 2019
12
Hi everybody!
For nearly a year I have designed a prototype touch switch for household use.
I tested with the household electrical device in my lab, It works very well, including resistive loads (such as drilling), led driver...
But, when I installed at some of my friend's apartments, it couldn't work. Touch operation is unstable, there is interference.
I was using commom choke mode filter in AC input...
I can't find the cause.
I hope to receive support from the community.
Thank you in advance!
 

ian field

Joined Oct 27, 2012
6,539
Hi everybody!
For nearly a year I have designed a prototype touch switch for household use.
I tested with the household electrical device in my lab, It works very well, including resistive loads (such as drilling), led driver...
But, when I installed at some of my friend's apartments, it couldn't work. Touch operation is unstable, there is interference.
I was using commom choke mode filter in AC input...
I can't find the cause.
I hope to receive support from the community.
Thank you in advance!
Clamp on EMI damping ferrites can help, some manufacturers fit them anyway.

When I serviced monitors for a living, I salvaged any I could find in scrapped items, but it must be possible to buy them. The best type are 2 "clamshell" halves of ferrite with a snap shut plastic jacket. You can put them on mains or signal cables - there's even slotted flat types for ribbon cable. Also both solid and clamped together.
 

MrAl

Joined Jun 17, 2014
6,782
Hi everybody!
For nearly a year I have designed a prototype touch switch for household use.
I tested with the household electrical device in my lab, It works very well, including resistive loads (such as drilling), led driver...
But, when I installed at some of my friend's apartments, it couldn't work. Touch operation is unstable, there is interference.
I was using commom choke mode filter in AC input...
I can't find the cause.
I hope to receive support from the community.
Thank you in advance!
Hi,

I can only guess you are using a microcontroller to do this probably an interrupt line or just an i/o pin.
For an i/o pin set to detect a change, it could pick up noise and trigger in a strange manner.
Perhaps a small value cap from the pin to ground or something.

Let us know what circuit you are using.
 

Thread Starter

nguyendai

Joined Mar 22, 2019
12
Hi,

I can only guess you are using a microcontroller to do this probably an interrupt line or just an i/o pin.
For an i/o pin set to detect a change, it could pick up noise and trigger in a strange manner.
Perhaps a small value cap from the pin to ground or something.

Let us know what circuit you are using.
Thanks for your reply!
Please check my designs bellow.
 

Attachments

AnalogKid

Joined Aug 1, 2013
8,219
On page 2 there are signal inputs named RL1 through RL4. Where do these come from?

If they come directly from the touch pads, then you have completely unprotected MOSFET gates hanging on antennae with no protection. One strong lightning strike nearby would fry all four of them.

What do the relays control? Are those loads suppressed?

You can buy IC's designed specifically for touch switch applications. Have you looked into them?

ak
 

mvas

Joined Jun 19, 2017
538
Thanks for your reply!
My schematic is bellow!
So, tell us about these Capacitive Touch Buttons?
Model # ?
Are your Capacitive Touch Buttons designed to be connected DIRECTLY to the Input Pin of your uP ?

I have used a Capacitive Touch Sensor IC, that required power, like this ...
http://ww1.microchip.com/downloads/en/devicedoc/40001946a.pdf

A Capacitive Touch Switch "Breakout Board" for testing ...
https://learn.sparkfun.com/tutorials/at42qt101x-capacitive-touch-breakout-hookup-guide

Where is your Capacitive Touch Sensor IC in your schematics?
How does your Capacitive Touch Button work?
 
Last edited:

DickCappels

Joined Aug 21, 2008
6,003
My guess is that you are using neutral as "ground". If so that's probably your problem. Your ground is not holding still with respect to the rest of the world. You could transformer isolate the circuit from the mains and use earth as a reference and that might solve your problem.

Also you may have it and I just don't see it, but some gate to source resistance, say a 33 Meg resistor might help a lot.
 

ian field

Joined Oct 27, 2012
6,539
Yes! It is capacitive touch switch!
Please check my schematic and tell me what is the wrong in design!
Might be worth having a browse through old 80s/90s TV schematics - some used touch switch channel buttons. We're talking about "live chassis" appliances here. Some even got away with neon indicator bulb bistables!!!
 

Thread Starter

nguyendai

Joined Mar 22, 2019
12
On page 2 there are signal inputs named RL1 through RL4. Where do these come from?

If they come directly from the touch pads, then you have completely unprotected MOSFET gates hanging on antennae with no protection. One strong lightning strike nearby would fry all four of them.

What do the relays control? Are those loads suppressed?

You can buy IC's designed specifically for touch switch applications. Have you looked into them?

ak
Thanks for your comment!
- Signal inputs named RL1 through RL4 is connected direct from IO MCU by a header on touch panel.
- I was using MSP340 MCU as touch sensing and controler
- Do you mean lightning is generated from the relay shut off?
 

Thread Starter

nguyendai

Joined Mar 22, 2019
12
So, tell us about these Capacitive Touch Buttons?
Model # ?
Are your Capacitive Touch Buttons designed to be connected DIRECTLY to the Input Pin of your uP ?

I have used a Capacitive Touch Sensor IC, that required power, like this ...
http://ww1.microchip.com/downloads/en/devicedoc/40001946a.pdf

A Capacitive Touch Switch "Breakout Board" for testing ...
https://learn.sparkfun.com/tutorials/at42qt101x-capacitive-touch-breakout-hookup-guide

Where is your Capacitive Touch Sensor IC in your schematics?
How does your Capacitive Touch Button work?
Thank you!
I was using MSP430 as a capactive touch sensing and MCU control peripheral, touch button with rounded shape, d = 13mm, ís implemented on PCB.
 

Thread Starter

nguyendai

Joined Mar 22, 2019
12
My guess is that you are using neutral as "ground". If so that's probably your problem. Your ground is not holding still with respect to the rest of the world. You could transformer isolate the circuit from the mains and use earth as a reference and that might solve your problem.

Also you may have it and I just don't see it, but some gate to source resistance, say a 33 Meg resistor might help a lot.
Thank you so much!
I hope your experience and share can help I solve problem.
I will try!
 

Thread Starter

nguyendai

Joined Mar 22, 2019
12
Hello again,

Are you using the "interrupt on change" feature of the microcontroller (done in software) assuming it has that as most do?
I didn't use MCU's interrupt feature, to detect changes of touch button i was using TI touch librarises RO methor.
 

Thread Starter

nguyendai

Joined Mar 22, 2019
12
Might be worth having a browse through old 80s/90s TV schematics - some used touch switch channel buttons. We're talking about "live chassis" appliances here. Some even got away with neon indicator bulb bistables!!!
Thanks!
I will study about your share!
 

mvas

Joined Jun 19, 2017
538
Thank you!
I was using MSP430 as a capactive touch sensing and MCU control peripheral, touch button with rounded shape, d = 13mm, ís implemented on PCB.
Application Report SLA842 - Capacitive Touch Design Flow for MSP430 MCU's With CapTIvate Technology
page 10 ... shows 470 ohm series resistors ?
( ... These resistors also help to lower the system emissions and improve RF noise immunity ... )
http://www.ti.com/lit/an/slaa842/slaa842.pdf
 
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