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 shows an
infrared close-object alert system built
around two popular and less expensive
integrated circuits: the LM555 timer
and CD4060 CMOS, 14-stage, ripplecarrying
binary counter/divider and
oscillator. At the heart of the circuit lies a
CNY70 reflective opto sensor module.
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 CNY 70 just happened to be
available. However, note that many different pinouts exist, so carefully
refer to the data sheets.
See associated figure