According to my dentist I should brush my teeth for 2 minutes. 30 seconds for each of the 4 quadrabts.
A lot of electric toothbrushes have a timer build in for this purpose, but because I use an old fashioned manual toothbrush which lacks such an option, an additional timer was needed. In principle a telephone could be used, but I leave my telephone in the livingroom. A simple stand-alone timer was needed here.
This timer must be started by a pushbutton and indicate 4 intervals of 30 seconds by a tone. After the 4th interval it should stop automatically. The user interface consists of only a start button and a small piezo speaker.
The most simple way to realize this is a small microcontroller. Because of my available infrastructure I preferred to use a member of the PIC-family of Microchip. The program I wrote is a very simple state machine which will even fit in the smallest and cheapes member of this family (PIC10F200). But I build the circuit on my universal PIC12 board and used a PIC12F509,
However the circuit is very simple and can also be build on a small piece of veroboard.
The sequence is started by pushing the reset button. After 2 seconds a tone indicate the start (state 1). Then after 30, 60, 90 and 120 seconds a tone indicates the end of a period (state 2 to 5). After the last period a second tone indicates the end of the program (state 6). The microcontroller is put into sleep which reduces the power consumption to nearly zero. An on-off switch therefore is not needed. For the power supply a small lithium cell of the CR2032 type in a battery holder can be used.
The program was compiled with the Knudsen C-compiler.

Using my universal PCB

components to be placed: C2=100nF, C6=10nF, R3=0, R4=0, R9=22k, IC1=PIC12F509, D1 and IC2 replaced by jumper, JP2=reset, JP3=optional
piezo speaker (passive) connected to 7 and 8, start button connected to JP2.
I mounted the battery holder on the board at the position of the relay.
Eventually an optical indication can be added: mount additional R2 and LD1