💠Opto fork sensor (Configured as an input with pull-up resistor)
💠Piezo sensor (Configured as an input with pull-up resistor)
💠Stepper motor
💠EEPROM
💠I2C protocol
💠LED
💠Buttons
💠 The device remembers its state even if the power goes off.
💠 After powering back on, it continues from where it stopped.
💠 If power is lost during dispensing, it recalibrates automatically without dispensing the pills.
The calibration process starts when the opto-fork is triggered. Following the trigger, the motor will run 2 full cycles to get the average steps per revolution. Once the system has the average steps, it can dispense pills. The system has three main functions for this purpose: motor running, calibration, and run function. These three functions are responsible for energizing the motor, calibrating it, and then dispensing the pills.
In this system, it saves the state each time it changes. To write and read it uses EEPROM and i2c protocols. In the main program, switch cases are used to decide which state to perform based on the EEPROM values.
The device mainly has two EEPROM functions: writing and reading. During the process, the system tracks three main states: calibration state, dispense state, and compartment number.
This state tracking helps to detect that the calibration is completed (ready to dispense pills), dispense completed, and the current compartment. These states are useful for running the motor properly even if there is a power failure during the dispensing and switch-off scenario.
If the average steps are available, the device is ready to dispense pills. It waits for the button press to start the process. When dispensing, it moves one compartment at a time, and there is a 30-second time duration between two dispenses.
Piezo sensor helps to detect whether the pill is dispensed or not. Piezo sensor is initialized as an interrupt and once it is triggered it will update the compartment number and move on to the next compartment. This process continues until all the pills are dispensed. If there are no pills to detect during the dispensing, then the system waits a minimum time to catch the event, if there are no pills detected during the waiting, the system detects this as ‘no pill dispensed’. It updates the situation and moves on to the next. Likewise, the dispensing process continues for a full cycle (7-compartment run) even if there are no pills.
If there is any power failure during the dispensing process, it means the compartment stops somewhere in the middle of the 2 compartment positions. Since the stop position is unknown in this case, it starts to recalibrate to detect the position. To do this, the motor will run in the reverse to the starting position and then move to the last dispensed compartment number. Once it repositions to the last dispensed compartment, it starts dispensing the pills again.
When the power is back it reads the compartment state from the EEPROM. Based on the state, it detects which process to run.
Here, we will dive into how the system works in detail. When the device boots for the first time, it assigns temporary states to all EEPROM variables. The reason is to avoid reading garbage values when EEPROM reads back. Once it has the temporary value, the software can perform normally. Once it assigns real value during the flow, the temporary values are no longer needed.
The system uses five memory addresses to write and read EEPROM data.
• DISPENSE_STATE_ADDRESS: Store state and non-state to check any errors.
• COMPARTMENT_NO_ADDRESS: Tracking the compartment number.
• COMPARTMENT_START_STOP_ADDRESS: Based on start and stop, it can detect the power failure situation (power loss during turning).
• AVERAGE_STEPS_ADDRESS: Helps to dispense pills after power off-on situation.
• CALIBRATION_STATE_ADDRESS: Based on the state (true or false) it detects the current situation of the device.
Pills are loaded only in compartments 1, 2, 4, 6, and 7. The remaining compartments are empty to demonstrate pill detection failures. A power loss occurred while the dispenser was at compartment 5.
Watch the demo video here!