Many robotic applications require a sensor to detect close or very close obstacles. Typically, reflective-type infrared sensors are used for this task. But the circuit in the figure 1 shows an infrared close-object alert system built around two popular and less expensive integrated circuits: the LM555 timer and CD4060 CMOS, 14-stage, ripple-carrying binary counter/divider and oscillator. At the heart of the circuit lies a CNY70 reflective opto sensor module.
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| Figure 1. | Using two common, inexpensive ICs and an opto sensor, this circuit detects and alerts an operator to the presence of a close object. Sensitivity is adjusted by variable resistor VR1. |
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The sensor contains a phototransistor and an infrared LED. The LED emits infrared light, and the phototransistor works as a receiver. When the opto sensor is illuminated, four red LEDs at the output of the circuit start flashing, in a special sequence pattern, to alert an operator.
This circuit also can be used to control an external electric/electronic load with the help of an optional electromagnetic or solid-state relay. The circuit works off a 9-V dc supply and can be powered by a compact PP3/6F22-type battery.
On power-up, current flows through resistor R1, and the LED inside the opto sensor is illuminated continuously. The LM555 (IC1) is wired as a light detector plus medium-current inverting line driver. Usually, its output (pin 3) is low. The value of sensitivity control VR1 affects the switching threshold, so adjusting the variable resistor will help to reduce unwanted detections caused by external light sources.
When reflected light from a close object falls on the phototransistor of the opto sensor, a current flows through VR1 to ground producing a voltage near to the positive supply level at the output of IC1. This activates the rest of the circuit. At the same time, a transistor-based relay switcher can be driven off IC1’s output (TP1).
The flashing alert light circuit is based on the CD4060 (IC2). Four bright red LEDs (D2-D5) are connected at IC2’s four outputs. Resistors R5-R8 limit the operating current (and hence the light output) of the red LEDs. Only four of IC2’s 10 outputs are used. The oscillating frequency is determined by the timing components R3 and C3. By varying these values, the designer can increase or decrease the output timing period.
Many opto sensors can be used; the CNY70 just happened to be available. However, note that many different pinouts exist, so carefully refer to the data sheets.
