Infra-Red Level Detector(BC327)

This article describes the Infra-Red Level Detector (BC327). The principle is very simple, very practical. The circuit components can help you understand better grasp this principle. For example, in this circuit, you can go to find and buy these components: BC327.

Useful for liquids level detection and proximity devices, Up to 50 cm. range, optional relay operation

This circuit is useful in liquids level or proximity detection. It operates detecting the distance from the target by reflection of an infra-red beam. It can safely detect the level of a liquid in a tank without any contact with the liquid itself. The device’s range can be set from a couple of cm. to about 50 cm. by means of a trimmer. Range can vary, depending on infra-red transmitting and receivingLEDs used and is mostly affected by the color of the reflecting surface. Black surfaces lower greatly the device’s sensitivity.

Figure 1 Infra-red Level Detector Circuit Diagram

Parts:

R1___________10K 1/4W Resistor
R2,R5,R6,R9__1K 1/4W Resistors
R3___________33R 1/4W Resistor
R4,R8________1M 1/4W Resistors
R7___________10K Trimmer Cermet
R10__________22K 1/4W Resistor
C1,C4________1μF 63V Electrolytic or Polyester Capacitors
C2___________47pF 63V Ceramic Capacitor
C3,C5,C6_____100μF 25V Electrolytic Capacitors
D1___________Infra-redLED
D2___________Infra-red Photo Diode (see Notes)
D3,D4________1N4148 75V 150mA Diode
D5___________LED (Any color and size)
D6,D7________1N4002 100V 1A Diodes
Q1___________BC327 45V 800mAPNPTransistor
IC1___________555 Timer IC
IC2___________LM358 Low Power Dual Op-amp
IC3___________7812 12V 1A Positive voltage regulator IC
RL1__________Relay withSPDT2A @ 220V switch Coil Voltage 12V. Coil resistance 200-300 Ohm
J1____________Two ways output socket

Circuit operation:

IC1 forms an oscillator driving the infra-redLEDby means of 0.8mSec. pulses at 120Hz frequency and about 300mA peak current. D1 & D2 are placed facing the target on the same line, a couple of centimeters apart, on a short breadboard strip. D2 picks-up the infra-red beam generated by D1 and reflected by the surface placed in front of it. The signal is amplified by IC2A and peak detected by D4 & C4. Diode D3, with R5 & R6, compensates for the forward diode drop of D4. A DC voltage proportional to the distance of the reflecting object and D1 & D2 feeds the inverting input of the voltage comparator IC2B. This comparator switches on and off theLEDand the optional relay via Q1, comparing its input voltage to the reference voltage at its non-inverting input set by the Trimmer R7.

Notes:

Power supply must be regulated (hence the use of IC3) for precise reference voltage. The circuit can be fed by a commercial wall plug-in adapter, having a DC output voltage in the range 12-24V.Current drawing:LEDoff 40mA;LEDand Relay on 70mA @ 12V DC supply.R10, C6, Q1, D6, D7, RL1 and J1 can be omitted if relay operation is not required.The infra-red Photo Diode D2, should be of the type incorporating an optical sunlight filter: these components appear in black plastic cases. Some of them resemble TO92 transistors: in this case, please note that the sensitive surface is the curved, not the flat one.Avoid sun or artificial light hitting directly D1 & D2.Usually D1-D2 optimum distance lies in the range 1.5-3 cm. 

 

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