Here is the circuit of a little label sensor ideal for detecting labels on bottles. The circuit offers a peak sensing distance of 2.5 mm (operating range 0.2 mm to 15 mm) backed up by the proven infrared diffuse-reflective technology.
At the heart of the circuit is a reflective optical sensor TCRT5000 from Vishay Semiconductors (www.vishay.com). The type TCRT5000 have a compact construction where the light-sender and the light-receiver components are arranged in the same direction to sense the presence of an object by using the reflective infrared beam from the object. The operating wavelength is 950 nm. The reflective optical sensor (OS1) is directly attached to the input of the photoelectric sensor main circuit based on the popular 8-pin dual-voltage comparator chip LM393 (IC1). Output from the voltage comparator is then processed by the output switch driver circuit wired around the far-famed 8-pin timer chip LM555 (IC2).
This “bipolar driver” circuit addition enables a selectable control output feature, i.e. the “light-on” or “dark-on” option. The light-on (LO) mode is the default mode outturns a logic-high (H) level from the label sensor through connector J1 wired to the TLP621-2 photocoupler (PC1) when reflected infrared light is received by the reflective optical sensor. In the dark-on (DO) mode, logic-high level output is available only when reflected infrared light is not received by the reflective optical sensor.
Construction of the Label Sensor project is extremely simple indeed, and it should be within the capabilities of complete beginners. The circuit can be built on a piece of stripboard. To some extent the way in which the unit is constructed and used will depend on the intended application. It can be built into a small plastic or metal box and connected to the external “electric-world” via the connector J1.
In the circuit, the LO and DO of the connector jack J1 are linked to respective open-emitter outputs of the photocoupler PC1. However, you can reverse this into open collector outputs with a slight intervention in the existing wiring. Application example of the label sensor is shown in the following figure.
TCRT5000 (online purchase – indicative links)