iot-cook-timer

minutes, seconds timeout cook timer

• features
• dev env
• hardware
• connections
• 3d print
• power management circuit
  • qucs
  • circuitjs

features

• set minutes, seconds add with push buttons
• countdown with progressbar
• key tones
• time expire audibile 10 sec sound
• standby power <0.00uA
• active power 18mA
• battery LiOn 3.7V power source
• autoshutdown after 10 sec

dev env

• vscode arduino
• arduino libraries ( available through Library Manager )
  • OneWire
  • Adafruit SSD1306
  • Adafruit GFX
  • arduino-utils

hardware

• atmega328p
• oled ssd1306 128x64 two wire interface
• piezo buzzer

connections

• schematics and pcb also available ready to print pcb labels
• power on
  • push button ( replace T0/T2 in schematics below ) ; this required for power on cycle
• atmega328p
  • GND
  • VCC from load power management circuit (see below)
  • SCL SDA to oled
  • digital pin 9 to piezo (+)
  • TX to serial RX (optional)
  • digital pin 5 to NPN transistor base ( replace T1/T3 in schematics below ) ; this required to maintain PNP transistor active until auto shutdown
  • digital pin 6 ( MINUTES ADD ) to push button pulled down with R10K to GND
  • digital pin 7 ( SECONDS ADD ) to push button pulled down with R10K to GND
  • digital pin 8 ( START COUNTDOWN ) to push button pulled down with R10K to GND
• serial (optional)
  • GND
• piezo
  • GND
• oled
  • GND
  • VCC from load power management circuit (see below)

3d print

• 3d print pieces front lateral with freecad src

power management circuit

qucs

• qucs simulation
• T0,T2 describe power on switch in a transient way ( T0 switches to close after 0.1ms enabling power while T2 switches to open after 0.3ms simulating push button release )
• T1,T3 describe digital pin 5 that maintains system on until pin goes low disabling main transistor Q2N3906
• RL represents atmega+oled consumption
• R3 is a pullup resistor to avoid Q2N main transistor draw a little current 0.3uA when system powered off
• graph shown power on switch (T0T2) at 1e-4s ; system autosustain (T1T3) at 2e-4 where Vm near 0mV ; power on switch release at 3e-4 with no effect due to BC547 activated transistor ; shutdown at 6e-4 by toggling T3 ( digital pin 5 low )

circuitjs

• see online