The timer for brushing your teeth, designed and manufactured by Instructables under the nickname basil.shikin, has no controls. If you take a toothbrush, it turns on itself by a signal from the weight sensor. A luminous scale of six divisions is turned on, the readings of which are reduced by one division every 20 seconds. Also, after 30, 60, 90 and 120 seconds from the beginning of the cycle, a signal sounds. Turning off all divisions coincides with the fourth signal, after which the cleaning can be stopped. After the brush returns to its place, the timer is ready for the next cycle. Scheme homemade consists of several parts:
1. The signal amplifier from the strain gauge on the INA12P chip on a small riser board (four-pin sensor, taken from cheap used scales):
2. The call control key on the TPS2024 chip (not to be confused with an oscilloscope of the same name):
3. The charge controller on the MAX1555 chip:
4. Control keys for incandescent lamps on transistors 2N3904:
The microcontroller is used type ATMega328p with external quartz at 16 MHz. The assembled board looks like this (masters who can solder well can put microcircuits on the board without panels), the display unit is not connected to it yet:
Files with a diagram and a drawing of the board are here. The board will look like this:
The master makes it using photoresist. LUT is also possible.
The wizard writes the software for the microcontroller and uploads it here, and he is taken for the manufacture of the housing and placement of components in it:
So the timer looks assembled. The casing is covered with two layers of Minwax primer and one layer of polyurethane varnish, the cracks are, if possible, sealed inside with hot melt adhesive.
Place the device so that when brushing your teeth it will not get splashes that can lead to warping of plywood, as well as corrosion of contacts in lamp holders. To charge the battery, the device must be moved from the bathroom to another room.