Vintage Toothbrush Timer

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:

Wake up
Read current weight with the precision of 3 grams
If current weight is less then the previous one play following sequence:
1. Turn on all lamps
2. Turn of a lamp every 20 seconds
3. Chime every 30 seconds
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.

mrlunna13 says: Oct 15, 2012. 1:38 AM

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

Great instructable! Very elegant!

Jesse M.

amaze1 says: Aug 22, 2012. 11:13 AM

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)

basil.shikin (author) in reply to amaze1Aug 26, 2012. 7:06 PM

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.

HelenaTroy says: Aug 20, 2012. 6:18 AM

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

Pfarmkid says: Aug 19, 2012. 3:15 PM

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

basil.shikin (author) in reply to PfarmkidAug 19, 2012. 3:34 PM

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

Pfarmkid in reply to basil.shikinAug 19, 2012. 6:16 PM

Sarcasm definitely you wrote great I just don't speak electronics

startree says: Aug 14, 2012. 3:57 PM

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! :)

physicsguybri in reply to startreeAug 19, 2012. 10:22 AM

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. ;-)

startree in reply to physicsguybriAug 19, 2012. 4:02 PM

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

physicsguybri says: Aug 19, 2012. 10:12 AM

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!

basil.shikin (author) in reply to physicsguybriAug 19, 2012. 3:33 PM

I thought that adding calibration button would make too complex of an interface. Weight readings are relative: if last time I read x1, I read x2 new and (x1 - x2) > E a toothbrush has been removed.