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  • Photoelectric Sensor Drawer Lock

  • Created: May 02, 2016

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Summary

The photoelectric sensors are devices that function similarly as ultrasonic sensors but it does not emit ultrasonic waves, instead it uses infrared light to detect the absence or presence of an object. The reference design features the PM-K45 photoelectric sensors from Panasonic Industrial Automation Sales, which functions as an input signal to trigger emergency drawer lock. The design uses ATTiny85 as the MCU process the output of the sensors. The output of the reference design will be an emergency lock mechanism.


The reference design is composed of two photoelectric sensors. The supply of the relay is separated from the MCU supply. The first sensor labeled, as U1 will be placed at side of the drawer that will emit continuous transmission of infrared light. The second sensor, which is U2, will be placed at the drawer lock, which the metal lock basically blocks the transmission of light. The operation of the circuit will have two scenarios to take place. First, if the drawer is being forced to open, the side of the drawer will block the light being emitted by the sensor, and then U1 will be sending output current to ATTiny85 PB3 pin. The ATTiny85 will be program to output HIGH at PB0 pin when U1 will be activated first, thus saturating transistor Q1 and activating the relay to trigger the mechanical lock which will fully stop the drawer from opening. The second scenario is when the drawer is open using a key. The light that the sensor U2 emitted is block by the drawers’ lock primarily and when using a key to unlock the drawer, the light will now pass through to the receiver side of the sensor U2, thus PB1 will be high and will bias Q2 and a green LED will indicate that it is open now. The ATTiny85 is also program to output low on PB0 if sensor U2 will be activated first resulting in not biasing Q1 to trigger the relay.


Adding additional features like buzzer, sirens, can enhance the reference design. The featured product PM-K45 photoelectric sensors can be used also to sense the starting point and overrun of a moving body and the starting point also of a rotating body.

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