Capacitive Touch On The Profile

[CoRe-M]

Merhaba arkadaşlar,

 

[rjenkinsgb]

Can you post photos of the LED strip showing its construction?

 

[CoRe-M]

LED şeritlerin içeriğini paylaşabilir misiniz?

Dokunma amacıyla PCB üzerindeki bir via pad üzerinden perçin kullanılarak profil anahtarı yapılır.

 

[rjenkinsgb]

OK, I was thinking from your original question (before I referred you to this site) that the touch switch contact strips were an add-on to a light; I now realise it's the entire metal body of the lamp.

That's a challenge!
Is the lamp body electrically connected to any part of the internal circuit?

 

[CoRe-M]

The metal body of the lamp is connected to the electronic board as a touch surface, and when any part of the profile is touched, the LED control is activated.

OK, I was thinking from your original question (before I referred you to this site) that the touch switch contact strips were an add-on to a light; I now realise it's the entire metal body of the lamp.

That's a challenge!
Is the lamp body electrically connected to any part of the internal circuit?

 

[rjenkinsgb]

I am confused - does the original built-in circuit work as a touch switch?, or, do you mean you have it connected to an external one you are trying to get to work?

 

[CoRe-M]

Kafam karıştı - orijinal dahili devre dokunmatik anahtar olarak mı çalışıyor, yoksa çalıştırmaya çalıştığınız harici bir devreye mi bağlı?

Profilin içinde gördüğünüz elektronik kart bir dokunmatik anahtar kartıdır. Profilin yüzeyinde dokunma algılamasını sağlayan bir via pedi aracılığıyla bir perçinle profile tutturulmuştur. Bu konuda tam olarak ne belirsizdir?

 

[rjenkinsgb]

OK. I got the impression from your original question (on my youtube video) that you were trying to adapt the design in the video to control the light! That's what was confusing me.

So, please correct me if I am wrong - The light was manufactured with that touch PCB built in, but the touch is not reliable? (I'll get it eventually !)

 

[CoRe-M]

OK. I got the impression from your original question (on my youtube video) that you were trying to adapt the design in the video to control the light! That's what was confusing me.

So, please correct me if I am wrong - The light was manufactured with that touch PCB built in, but the touch is not reliable? (I'll get it eventually !)

Robert, the topic I mentioned under the video is exactly the same here—there’s no difference. I designed this board myself, but I haven’t been able to achieve full efficiency. Since I’m using a plug-in SMPS adapter, there's noise in the DC voltage. The second problem is that the LED strip PCB is attached directly to the aluminum, which somewhat affects the capacitive sensing. I'm doing R&D to find a solution for this.

 

[rjenkinsgb]

OK, got it.

Can you add an earth ground (AC power socket ground) to the PSU negative output?

The switch electronics need a good enough ground (literal or capacitive) so a decent level sense signal is applied to the sense electrode, relative to that ground.

Most things use the bulk electronics as the ground with a relatively small touch contact; your setup is almost inverted from that! It needs some form of reference ground, to be able to both drive the sense signal and compare the touch contact signal to the electronics ground.

Do you have an oscilloscope, so you can look at the signal and the noise level & frequency on the casing & PSU output?

Other than that, I think you need to try different PSUs to find a type that has a cleaner output with no common mode noise.

 

[CoRe-M]

OK, got it.

Can you add an earth ground (AC power socket ground) to the PSU negative output?

The switch electronics need a good enough ground (literal or capacitive) so a decent level sense signal is applied to the sense electrode, relative to that ground.

Most things use the bulk electronics as the ground with a relatively small touch contact; your setup is almost inverted from that! It needs some form of reference ground, to be able to both drive the sense signal and compare the touch contact signal to the electronics ground.

Do you have an oscilloscope, so you can look at the signal and the noise level & frequency on the casing & PSU output?

Other than that, I think you need to try different PSUs to find a type that has a cleaner output with no common mode noise.

You're amazing, Robert !

Your observation and analysis are absolutely correct. The DC negative rail definitely needs a proper ground reference. Unfortunately, the PSU we are using does not have a grounding connection, and adding one is not possible. I need to find a way to create a virtual or analog reference by hardware means. Interestingly, when I touch only the negative rail with the black probe of a Fluke multimeter (leaving the positive probe floating), it seems to establish a reference and suppress the noise. The DC negative rail appears to be too floating, and this causes reference drift in ADC measurements. There must be a way to solve this.

 

[rjenkinsgb]

The switch circuit needs an external ground reference so the electronics have a reference to measure relative to.

If the PSU DC wiring is the only option, then you have to use a sense frequency well away from that with some kind of filtering at the sense input, so the touch "drive" signal can be measured without the PSU noise swamping it.

Do you have a scope?

 

[CoRe-M]

The switch circuit needs an external ground reference so the electronics have a reference to measure relative to.

If the PSU DC wiring is the only option, then you have to use a sense frequency well away from that with some kind of filtering at the sense input, so the touch "drive" signal can be measured without the PSU noise swamping it.

Do you have a scope?

I didn't quite understand what you meant. Could you please explain it in more detail, Robert?

 

[rjenkinsgb]

Again, do you have an oscilloscope?

Until you know the frequency and amplitude of the problem noise from the switched mode PSU, there is no way of knowing what is needed to work around it, if that is possible.

 

[CoRe-M]

Again, do you have an oscilloscope?

Until you know the frequency and amplitude of the problem noise from the switched mode PSU, there is no way of knowing what is needed to work around it, if that is possible.

It is unrealistic to expect clean and stable noise performance from low-quality switch-mode adapters that do not comply with EMC or EMI standards. If a motor or other inductive loads are connected to the same mains line, the adapter directly transfers that noise to the DC output. When I tested it with a linear transformer-based power supply, it worked flawlessly and very reliably. In conclusion, it is necessary to design an analog circuit that can operate properly in such noisy environments. You had mentioned a differential schematic under the video, and I was curious about that. Could you share it?

 

[rjenkinsgb]

You had mentioned a differential schematic under the video, and I was curious about that. Could you share it?

That was when I thought you were adding touch strips to a normal plastic fitting.
By using two, one either side, the noise would be balanced and touching would unbalance it.

As the entire metal casing is the "touch contact" that approach does not apply.