Using capacitive sensor on the metal base of a lamp

Hi Yoann,

Very interesting and really cool product and thanks for sharing the website. 

If the need is to snooze the alarm and if the expectation is for the users to touch the metal base I recommend using our Inductive sensing technology which can essentially detect a deflection of a touch on metal. The capacitive sensing devices like the FDC2214 and FDC1004 are extremely sensitive and there is a potential that it can trigger false alarm. 

As the base of lamp is metal, using teh metal as a trigger our inductive sensing device can detect the touch and will let you take action. This can be immune to moisture and also could detect if a person if wearing gloves. 

For more information on the inductive sensing please refer to our FAQs https://e2e.ti.com/support/sensors/f/1023/t/295036 

Hi Arjun,

Thanks a lot for your quick and kind response!

I read some stuff about inductive sensing, but didn't think that it was something to look at for our need, would definitely do it now!

I'll come back to you if needed, or to let you know if it works well.

Have a good day!

Best regards,

Yoann

Hi Yoann,

An alternative could be the Captivate capacitive touch technology. It can work on metal, glass, plexiglass. I have even seen a demo on Wood...

For metal a slight metal displacement is usually needed. But if the metal touch is isolated (ie connected to earth) from the sensing electrode then you might be able to sense touch or even proximity depending on how you setup the sensitivity. The Design center GUI enables an easy evaluation.

The Captivate-metal section or the technology guide provides info on the use case when a small metal displacement occur:
http://software-dl.ti.com/msp430/msp430_public_sw/mcu/msp430/CapTIvate_Design_Center/latest/exports/docs/users_guide/html/CapTIvate_Technology_Guide_html/markdown/ch_evm_CAPT_METAL.html

If the metal surface is isolated from the touch electrode then no metal displacement is needed. So you can look at the standard use case on glass and plexiglass like on the CAPTIVATE-PHONE demo board:
http://software-dl.ti.com/msp430/msp430_public_sw/mcu/msp430/CapTIvate_Design_Center/latest/exports/docs/users_guide/html/CapTIvate_Technology_Guide_html/markdown/ch_evm_CAPT_PHONE.html

I would advise to look at the online training serie:
https://training.ti.com/captivate-training-series

A.

Hi again Arjun,

I took a look at the documentation you sent me, and from what I understand, the inductive sensing is used to detect a movement of a metal piece, but in our case, the metal is quite thick and won't move by touching it.

It also needs to design a coil at a specific location to detect this movement, but in our mind, we would like to be able to snooze the alarm by touching the base anywhere, not at a specific location, so I'm not sure if inductive sensing is the best for us.

Let me know if I understood wrong.

Best regards,

Yoann

Hi AnBer,

Thanks for you response! I will take a look at this technology, and keep you udpate with my investigations or questions if needed.

Have a good day,

Yoann

Hi Yoann,

Yes, you are correct. For inductive sensing technology you need a metal that needs to be deflected and the change in the deflection will be detected a metal press. Depending on the design the deflection can be in the order of 100s um for LDC to detect a metal press. 

If you are looking at just touching the base capacitive sensing would work the challenge is going to be where and how is the señor going to be connected such that the lamp is going to detect a change in capacitance. 

Let us know how and which direction you like to proceed. TI does have inductive and capacitive solutions for your application :) 

Hi Arjun,

The metal in our case is a 2mm thick aluminium, and I don't think that it moves at all when touched. I was thinking that it would be as easy as using something like this, but apparently it's not that simple..

I'm looking at the CapTIvate technology now that AnBer suggested, and from what I understand of the Proximity Range Test section, it can be used with an external electrode (ie not on the PCB) without a GND reference; in our case we don't need a proximity sensor, just a touch sensor, but my assumption is that it can be change by playing with sensitivity, right?

Yoann

Hi again,

So after spending the afternoon reading the very nice explained CapTIvate™ Technology Guide, I think that we'll order a CAPTIVATE-FR2633 with its programmer board to do some tests, and if everything's going well, I'll add a MSP430FR2512 to our design, as we only need one sensor input.

What do you think about this approach?

Best regards,

Yoann

Hi Yoann,

As you mentioned the CAPTIVATE-PGMR + CAPTIVATE-FR2633 should enable you to do some rapid prototyping with running the Design center GUI on the PC.
You could test with using some copper foils as electrodes and fixe it on the lamp body (with an isolation foils between the lamp body and the electrode).
The lamp body might need to be connected to hearth so that it does not disturbe the sensing.

The "worshop getting started" should help you :
http://software-dl.ti.com/msp430/msp430_public_sw/mcu/msp430/CapTIvate_Design_Center/latest/exports/docs/users_guide/html/CapTIvate_Technology_Guide_html/markdown/ch_workshop.html#

It is very likely that the MSP430FR2512 should be enough for this type of application. The MSP430FR2633 is the sub-set and you could mimic a FR2512 by using 1 single sensing unit.

A.

Hi Yoann,

please find below an additional AN referring to CapTIvate on metal.

Regards

Kostas

Hi AnBer,

I will try that and let you know how tests are going in the following weeks. Thanks again for your help! Very appreciate.

Thanks Kostas also for the documentation you sent.

Yoann

Hi Yoann,

Enjoy the testing!

For further/new questions linked to Captivate (ie MSP430FR2xxx) then please use the according MCU forum:

https://e2e.ti.com/support/microcontrollers/msp430/f/166

Hi AnBer,

Ok I'll do that! Have a great day!

Yoann

Hi AnBer,

Thank you for your help!! 

Hi Yoann,

Please let us know how this project goes. We are glad that you are choosing TI for your products and I must say the lamp does look really cool. Meanwhile I am goin to close this thread and please feel free to jump in when needed.