# Vintage Toothbrush Timer

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My last visit to the dentist convinced me that I should really brush my teeth at least two minutes. I decided to build a special toothbrush timer: it would detect when a brush is taken out, measure two minutes and notify when the time is up.

I chose to use Atmega328p, a weight sensor, brass cups, a tray, old alarm clock's chime and some plywood. I would like to tell how this device was made: what electrical components were used and how I assembled the enclosure.

Here is a video with how it all works togather:

An algorithm is quite basic:
1. Wake up
2. Read current weight with the precision of 3 grams
3. If current weight is less then the previous one play following sequence:
4. 1. Turn on all lamps
2. Turn of a lamp every 20 seconds
3. Chime every 30 seconds
5. Sleep for 8 seconds

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## Step 1: Circuit Design

The circuit is designed around a wight sensor. I got one from a used digital scales. It is a pretty basic device: there are four wires: one is input current, one is ground and voltage difference between the other two wires is determined by a weight of an object on the scales. The difference, however, is really small, so one needs to use an amplifier to be able to tell that the weight has changed.

Here are components that I chose:

ATMega328p with 16Mhz crystal – I chose this micro-controller because it is extremely easy to use. There is also a good  community support, as ATMega328p is used in one of Arduinos.

Ina12P amplifier – this device is created specifically for amplification of sensors' signals. It is not hard to use it. The only thing that I found tricky is figuring out the right resistance value for amplification gain.

TPS2020 switch – this is a great switch with a very low standby current ( <10 μA). I use it to control power of the servo that chimes.

MAX1555 charger – this device controls charging of device's lithium-ion battery.

2N3904  transistors – used to control lamps' power.

Lamps – I chose incandescent lamps out of esthetic reasons. Since I wanted to give the project a "vintage" look LED lamps did not quite fit the design. Although these lamps consume more power the feeling they evoke is quite worth it.

This device is able to work 3 weeks on a single charge.

Full schematic could be found on Github.

## Step 2: Printing the Circuit

I used photo-resistive method to etch the circuit.

## Step 3: Programming

There program is pretty strait-forward. Source code could be found on GitHub.

## Step 4: Enclosure Design

The design and assembly of project's enclosure was almost as exciting as building and programming its circuit. I started with a new document in Inkscape and a new sheet of plywood I got from a hardware store. I have rented a laser cutter in Techshop to cut the plywood according to my design. The ease with which the cutter created my parts is quite fascinating:

I used glue to put everything together. All of the edges were reenforced with triangles cut from the same plywood.

I have applied two layers of Minwax wood finish and a layer of their Polyurethane to protect the surface.

I have applied some hot glue to all of the edges: this sealed the enclosure and made it somewhat water-proof. Importance of this step can not be underestimated, as the time would reside in a damp place.

## Step 5: Putting Everything Together

Once the enclosure was ready I have put the circuit inside and connected all wires. Photographs attached to this step show how it all fits inside.

I also hope this device will inspire you to create some creasy contraptions of your own!

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## 17 Discussions

I L-O-V-E the copper cups!! They would make great velocity stacks in my motorcycle.

Great instructable! Very elegant!

Jesse M.

Just to say the cups are in copper, not brass (unless color changing due to the camera). Brass is a copper ALLOY (with zinc) and is yellow. My father is a coppersmith, by the way.

But most important: GREAT idea, definitely FAVE for me !!

(I made one with white diffused leds in a vitamin tube, but yours is better for sure)

You are quite right: the cups are copper, not brass. The dish seems to be brass indeed. My bad.

It really shows after first month of use: the metals change their colors differently because of stains of water and tooth paste. I don't rush to clean it though: I think it adds to the character of the contraption.

I went a much simpler route to time my teeth-brushing - I have a hourglass-tyupe egg timeer, which lives on the sehlf above my bathroom sink. I turn it when I start brushing and carry on till I notice that the sand's all run out

After reading this I decided that it may look like English but this is obviously a lot more complicated of a language with smarter people speaking it

2 replies

Hm... Not entirely sure if I read sarcasm. If so, you are absolutely right â English is my second language indeed.

i have no idea what i'd do with this but it's very cool... i was thinking you could adapt it for an egg timer, (with little egg cups instead of toothbrush cups) etc etc, excellent for those of us losing our marbles and can't recall what we were doing a minute ago! :)

2 replies

I'd say it would work well to detect the loss of marbles. Of course at that stage we might not be able to understand what the blinking light counter means. ;-)

Man it took me a minute already to work ou what you were talking about! I'd better get started making my marble counter or whatever it was I was planning to make before its too late :D Cheerio

Very cool and nicely built! Is the weight sensor fixed calibrated or do you have a push-button calibration for when additional toothbrushes are placed in the brass cups? I.e. holding button down for >= 3 sec updates weight calibration offset with new present weight.
Again, great job!