This Automatic Liquid Dispenser with Proximity Capacitive Sensing reference design is for hands-free dispensing of liquids such as soap, hand sanitizer, shampoo, or hand lotion. Automatic liquid dispensers are popular and eliminate bacterial transmission with touch-free designs. In recent years, these dispensers have helped prevent COVID-19 infections. The liquid dispenser distributes a set amount of liquid using motion activation to minimize waste. When a hand is detected near the nozzle, the MCU triggers the pump motor and the dispenser emits liquid. The liquid is automatically dispensed without any touching of any part of the nozzle, resulting in a more hygienic environment.
The general method for detecting a hand approaching the nozzle of the liquid dispenser is to detect the blockage of optics from the infrared LED to the phototransistor. This solution uses the electrode board and the capacitive sensor unit (CTSU2L) of the RL78/G23 MCU to detect a hand approaching the nozzle, eliminating the need for infrared LEDs and phototransistors and reducing the number of parts and the power consumption. The logic and event link controller (ELCL) is used to activate the capacitive sensor unit, providing even lower power consumption, and the RL78/G23 MCU drives a pump motor that dispenses liquid by detecting a change in the capacitive state in the capacitive sensor.
This reference design also features the ISL9001A high performance low dropout linear regulator, which is used for power management and can source a current of up to 300mA. This regulator helps extend battery life as it supports a wide input voltage range (2.3V to 6.5V) while featuring extremely low quiescent current.
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- Demo board includes the RL78/G23 MCU
- After the system is powered on, the system operates in low power consumption mode in most of the conditions to obtain longer battery life
- If hands are placed under the nozzle, an LED and buzzer are turned on to indicate liquid dispensing
- Even if hands remain under the nozzle, liquid dispensing has a maximum duration of 2 seconds
- If the battery voltage is lower than 4.8V, an LED blinks to indicate a low power condition when hands are placed under the nozzle
- Sensing method: Proximity Sensing by the Capacitive Sensing Unit (CTSU2L)
- Sensing distance: 2.5 to 3.5 cm
- Amount of liquid per motion activation: 0.5ml/0.8ml selectable