DIY Toothbrush Timer -- Episode 480

Do you make sure you brush for 2 minutes each time you brush your teeth? Today I’m making a timer to ensure I do! However rather than just coding it on a dev board, why not do it entirely microcontroller free and design it as a circuit using 555s and 74 series logic?

Bill of Material:

Product Name	Manufacturer	Quantity	Buy KitBuy Kit
IC, TIMER, 555, PDIP8	TEXAS INSTRUMENTS	1	Buy Now
Shift Register, 74HC594, Serial to Parallel, 1 Element, 8 bit, DIP, 16 Pins	TEXAS INSTRUMENTS	2	Buy Now
Logic IC, Inverter, Hex, 1 Inputs, 14 Pins, DIP, 74HC04	TEXAS INSTRUMENTS	1	Buy Now
Signal Relay, 3 VDC, DPDT, 2 A, P2/V23079 Series, Through Hole, Latching Dual Coil	AXICOM - TE CONNECTIVITY	1	Buy Now
2N3904, Bipolar (BJT) Single Transistor, NPN, 40 V, 200 mA, 625 mW, TO-92, Through Hole	MULTICOMP PRO	1	Buy Now
LED, Red, Through Hole, T-1 3/4 (5mm), 20 mA, 2.1 V, 630 nm	CREE	12	Buy Now
Industrial Pushbutton Switch, 15.2 mm, SPST, Off-(On), Round, Blue	MULTICOMP PRO	1	Buy Now
MF25 2K7, Through Hole Resistor, 2.7 kohm, MF25 Series, 250 mW, ± 1%, Axial Leaded, 250 V	MULTICOMP PRO	12	Buy Now
MF25 3K, Through Hole Resistor, 3 kohm, MF25 Series, 250 mW, ± 1%, Axial Leaded, 250 V	MULTICOMP PRO	1	Buy Now
Through Hole Resistor, 1 kohm, MCRE Series, 125 mW, ± 5%, Axial Leaded, 200 V	MULTICOMP PRO	1	Buy Now
MCF 0.25W 10K, Through Hole Resistor, 10 kohm, MCF Series, 250 mW, ± 5%, Axial Leaded, 250 V	MULTICOMP PRO	4	Buy Now
Through Hole Resistor, 3 Mohm, MRS25 Series, 600 mW, ± 1%, Axial Leaded, 350 V	VISHAY	1	Buy Now
Electrolytic Capacitor, 4.7 µF, 35 V, MCGPR Series, ± 20%, Radial Leaded, 2000 hours @ 85°C	MULTICOMP PRO	1	Buy Now
Electrolytic Capacitor, 10 µF, 35 V, MCGPR Series, ± 20%, Radial Leaded, 2000 hours @ 85°C	MULTICOMP PRO	1	Buy Now
Multilayer Ceramic Capacitor, 0.1 µF, 50 V, Mono-Kap Series, ± 10%, Radial Leaded, X7R	VISHAY	5	Buy Now
Multilayer Ceramic Capacitor, 10000 pF, 50 V, Goldmax, 300 Series, ± 10%, Radial Leaded, X7R	KEMET	1	Buy Now
1N4001+, Standard Recovery Diode, 50 V, 1 A, Single, 1.1 V, 30 A	MULTICOMP PRO	2	Buy Now
IC & Component Socket, 8 Contacts, DIP Socket, 2.54 mm, 2227MC Series, 7.62 mm, Phosphor Bronze	MULTICOMP PRO	1	Buy Now
IC & Component Socket, 16 Contacts, DIP Socket, 2.54 mm, 2227MC Series, 7.62 mm, Beryllium Copper	MULTICOMP PRO	2	Buy Now
IC & Component Socket, 14 Contacts, DIP Socket, 2.54 mm, 2227MC Series, 7.62 mm, Beryllium Copper	MULTICOMP PRO	1	Buy Now
LED Housing, 9.5 mm x 12.5 mm, Black, Plastic, 5mm / T1 3/4 LEDs	KINGBRIGHT	12	Buy Now
Plastic Enclosure, Multipurpose, Plastic, 120 mm, 80 mm, 59 mm, IP54	HAMMOND	1	Buy Now
2465, Battery Holder, AA x 3, Wire Leads	KEYSTONE	1	Buy Now
Prototyping Board, FR2, Epoxy Paper, 1.5mm, 100mm x 160mm	ROTH ELEKTRONIK	1	Buy Now
221-612, Pluggable Terminal Block, 2 Ways, 20AWG to 10AWG, 6 mm², Push In Lock, 41 A	WAGO	4	Buy Now