💬 No neutral power supply/relay board for in wall switch

[mtiutiu]

As promised the final design! This is for one channel which I will use mostly in my house. The backside is 3d printed and it holds the electronics. The front panel and fake button are bought from the local store (Leroy Merlin) and I like it very much (it's part of modular switches design and it's very cheap). I could 3d print the front side plastics..but it I can't get the same look and feel - can't beat the molded plastic with a 3d printer for now ... (well you could use some resin or other stuff to fill the holes and then spray paint but still it's a lot of work and it doesn't worth imho)

Here are some pictures from the design. I will post later the pictures with the real product also.

[mtiutiu]

And the real product pictures now:

Short demo of touch functionality (will post later on the bluetooth mesh network functionality):
https://streamable.com/b52qb
https://streamable.com/dj3z7

Sorry for the solder bridge replacing the R20 inrush current limiting resistor..that's just temporary until I get the real component :smile: . And yes, the capacitor across the bulb is still needed but it's a very small one of 0.1uF/250Vac and it should fit near the light bulb on the ceiling (only one is needed if there are two light bulbs on the same circuit).

The aluminum foil wrapped around that sponge is to "extend" the capacitive sensor so that it reaches the front plate fake plastic button. The 3d printed clear plastic around it is to hold it in place and also to spread the small leds light.

Everything is custom made except for the front plastics.

[mtiutiu]

For those interested I started "documenting" my work and what I achieved so far on my blog (first time I'm "blogging" :) ).

[scalz]

@mtiutiu
congrats :clap:
I'm curious, are you happy with range (I noticed you changed a bit the rf reference design routing).
I guess you use BLE mesh regarding average power consumption (which should improve range too), so rfm69+mysensors is maybe too power hungry?
Well, I think I'll try to assemble a few of your boards, this might be the first design I try here :nerd_face:
thx for sharing, I can imagine it was lot of work and time.

[mtiutiu]

@scalz
Thanks.

To answer your questions:

• Range is not that "big" if having multiple walls - if more than 1-2 walls things start to degrade but having more nodes in the mesh helps to overcome this. Also one can tune the number of retransmits as shown on my blog and having more relaying nodes will help a lot also. Of course my custom RF design is not perfect or that optimized. Add to that the ceramic antenna which is not that great...
• Power consumption is a plus also indeed as per node I get around 7mA x 3.3V ~ 24mW. Let's add to this the leds and touch capacitive sensor and make it 30mW on average but no more than that. I enabled the internal DC-DC converter of the MCU and add to that the fact that the nodes will stay more in RX mode hence the 6-7mA constant current draw.
• The boards are a little bit different but not much from a RF performance point of view (I'm still learning this part when it comes to PCB layout)
• The hatched ground plane differs around the capacitive pad(s) but that's because the PCB was designed initially using EasyEDA which offers "90 degree" hatches. Then I ported the PCB to KiCAD where I had to do a little trick with some polygons at 45 degree as it doesn't support hatched ground planes (not now at least or in the stable version).

I tested already both designs - the original one and the KiCAD conversion also and both are working as expected.

Yes it was lots of work and especially the power supply PCB design for which the main inspiration was the DER-622 application note from Power Integrations.

But I'm very happy with the overall result. I will update the blog with some real life videos of the whole system in action in the near future also. There will be more blog entries targeting this topic - that's for sure.

[berkseo]

Will software be available for testing?

[mtiutiu]

@berkseo

Yes, it's available here. The documentation is a little bit scarce I admit but if you understand Apache MyNewt and its build system it should be pretty straightforward theoretically.

I will add more details when I have the time. The code was tested and it's in production. Works without a glitch so far.

[Justin Steven Vanegas Salazar]

Hello,

I looked for the manufaturer part of C10 in EasyEDA Library "CC0603KRX5R6BB684" and I noted that it describes a 680nF/10V capacitor, but in the schematic it is supposed to be 100nF/50V, (CC0603KRX7R9BB104), so which is correct?

[Justin Steven Vanegas Salazar]

It is a amazing project indeed. I want to repeat the project too, by any chance, do you have the CPL file for the PCB Assembly?

[OldSurferDude]

The LNK364 has an internal 6.3V zener diode across BP and S so the 10V is OK, though the 50V is probably a better idea. The data sheet indicates the capacitance should be 0.1 μF (100nF). I'd recommend the latter. (It could be a typo in the EasyEDA)