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16. Applications and implications

I have decided to make the doorbell as my final project. This in an idea I had from the start and used for the weekly assignments. However, I then kind of lost interest on it and just left it were it was.

I had some more ideas that I actually considered, but I have come to the realization that time will run out. Therefore, this is the project I will take to the finish line.

Idea recap

The design is a two-part doorbell where the parts sandwich a glass window or wall using magnets to hold on.

Pressing a button on one side will release sound on the other side. Ideally only the inside part (which releases the sound) would need power. This presents some interesting design challenges.

What will it do?

The doorbell provides auditory notification that someone is on the other side of a glass wall or window. For example in an office type environment where person might not be looking at the door.

Who has done what beforehand?

This project will be built individually and I did not find any relevant references searching the Fab Academy page. There were some search results about smart doorbells but those didn't seem relevant for my project.

I will be taking advantage of many arduino libraries however. For example I will be using a ready made library for sending and receiving infra-red (IR) signals.

What I failed to research beforehand was searching the obvious term "through-glass doorbell" on the internet. One of our instructors found this which is an interesting and probably more convenient project. It's using the change in capasitance to sense the proximity of a hand through the glass. The end result is in many ways more practical to mine, but making a similar one would be pointless for me (no learning) unless I expanded on it greatly. For this reason I will stick with the challenges set by my approach.

What will you design?

All of the required 3D models and the one PCB needed are designed by me. So no existing designs will be used. All of the physical parts will be designed in 3D This includes 3D printed, laser cut and also CNC milled parts. For the sake of completeness (and meeting the requirements) I will design an doorbell icon of sorts in Inkscape that can either be laser engraved on the button or a sticker with the vinyl cutter.

What materials and components will be used?

I did prepare this bill-of-materials (BOM) a couple months ago. That one is slightly outdated as some components have changed, but otherwise it's pretty comprehensive.

Here is the updated BOM:

Item Purpose Part ID Quantity Unit Price Link
Magnet ⌀ 13 X 5 mm attaching - 8 ~1 € Fab Lab
Seeed Xiao brains any 1 5 € Seeed Studio
IR diode emittor HIR11-21C 1 0.95 € Digikey
IR receiver detector TSOP38238 1 ~1 € Digikey
Buzzer sound CEM-1203(42) 1 0.68 € Digikey
Circuit board electronics - 25 x 50 mm <1 € Fab Lab
Resistor 49.9 Ω limit current on diode 49A9 1 0.09 € Fab Lab (digikey)
PLA (black) insides - 68 g 1.4 € (generic)
Plywood 4 mm Magnet frame - ~200 cm2 <1 € Mahogany.fi
Plywood 0.4 mm Magnet frame - ~200 cm2 <1 € Mahogany.fi
Wood button cover - ~100 cm3 €€€ self-provided
Mirror-like material reflect the IR signal - 2 cm2 <1 € example
Total price ~15 €

Main change is from a laser to a regular IR diode and a receiver. Also omitted spring, batteryholder and the mirror. The spring and batteryholder are trivial and might be replaced by self designed components. The mirror could be replaced by just a white surface (even paper) as that should be enough for the IR diode.

Only question is still what kind of buzzer I will use.

Where will they come from?

The IR receiver is part of this set. We have some amount of those kits at our Fab Lab. All of the other components are also provided by the Fab Lab unless otherwise stated. Most of those are also part of the fab lab inventory.

How much will they cost?

Very little, somewhere from 10 to max 20 euros. Mainly the Seeed Xiao and the magnets add to the cost.

What parts and systems will be made?

The project has two parts, the inside unit and the outside unit. These will sandwich a glass window (or other thin wall) with magnets.

The inside unit has an IR diode, an IR receiver and all the other electronics. The outside unit will reflect or not reflect the IR signal back based on the position of the button. This allows the inside unit to detect the button presses on the outside unit and activate the buzzer.

What processes will be used?

3D printing, laser cutting and CNC milling (wood) most likely. Also the PCB will be manufactured with a milling machine.

What questions need to be answered?

  • Does the magnet hold enough through the glass?

  • Does the infra red go through the glass?

    • TV remote and a phone camera suggests so..

    • Does it come back?

      • YES!

    • Does it leak by reflecting inside the glass?

      • Seems to not be an issue due to the low intensity of the IR diode.

    • What signal is sent?

      • Most likely an arbitrary NEC signal as learned in output week.

  • Does the material of choice (PLA) block IR (atleast enough) ???

    • Might need to use plywood where applicable.

    • Maybe Polyterra has enough other ingredients to block IR?

    • This wasn't really an issue.

  • Which side of the PCB the microcontroller is mounted?

    • Using straight pin connectors it could be easily put on the otherside of the board to allow unrestricted placement of the IR diode and receiver.

    • Do that.

  • How is the IR receiver mounted and connected

    • As it is a separate module.

    • Desolder the pin connector and solder to main PCB in an angle.

  • How is the buzzer mounted and connected?

    • Found the kind of buzzer that can be soldered on the board. Solder it with through holes to have it facing away.

  • How are the possible batteries mounted and connected?

    • No batteries in this version.

How will it be evaluated?

Successful project should be evaluated agains the following criterions (in the order of importance):

  1. Reliably detects the button presses

  2. Stays on the glass door of Fab Lab Oulu

  3. Works when mounted on the glass door of Fab Lab Oulu

  4. Pressing of the button is satisfying

    • This is subjective (by intention), but I was aiming to have some tactile clicking on the button. As that failed the other end for "satifying" could be that it's "big button that can be smashed"

  5. Looks nice

Schedule

Here is my planned schedule for the implementation of this project. I have very limited time left but starting from today I will try and finish this before the end of next week.

Date Day Tasks
2023-05-19 Fri 3D design and test buzzer
2023-05-20 Sat Finish wild card and bicycle repair
2023-05-21 Sun Design new PCB and program microcontroller
2023-05-22 Mon Manufacturing day:
3D print, CNC, PCB & soldering
2023-05-23 Tue Test, demonstrate and fix
2023-05-24 Wed Create the video
2023-05-25 Thu Finalize documentation
2023-05-26 Fri Buffer day

Actually achieved schedule

Date Day Progress
2023-05-19 Fri Acquired and tested the buzzer
Designed the outside part
Designed the inside part
2023-05-20 Sat Designed the inside part
Serviced bicycle
Finalized wild card week
2023-05-21 Sun Designed the new PCB
Finalized wild card week (kinda)
Print some test pieces
Program the microcontroller
Laser cut the magnet frame
2023-05-22 Mon 3D print most of the parts
Mill & solder the PCB (couple times)
CNC mill the wooden cover
2023-05-23 Tue CNC mill the wooden cover
Test, troubleshoot & fix
Break (& fix) IR receiver multiple times
2023-05-24 Wed Finish the wooden cover
Create the video
Fix some other weeks' documentations
2023-05-25 Thu Finalize project documentation
2023-05-26 Fri Mill the material produced in wildcard week
Fix some other weeks' documentations
Create the video
2023-05-27 Sat Mill the material produced in wildcard week
Finish wildcard week documentation (this time for real)
Finalize project documentation
(This was partly done but finishing would be done later)

End of week 16.