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Implementing Infrared Object Detection(74HC04)

2017-02-24 21:02  
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This article describes the Implementing Infrared Object Detection (74HC04). The content is very simple, very practical. The components of the article can help you understand better grasp this principle. For example, in this part of the principle, you can go to find and purchase the components: 74HC04. 

This page is going to describe the parts, schematic,
softw1are, and some tips on using Infrared for object detection.
The parts used are typically the same parts found in most
consumer electronic remote controls, and are widely available. If
you have an old TV or other IR remote device, you have
the makings of a nice IR detection system.

The Parts

The tw1o basic parts for working with IR are the emitter and
the detector. The emitter is typically an LED that emits
near-infrared light. A typical wavelength is 880nm, which is just
beyond the human eyes ability to see. Many suppliers, new and
surplus, can provide you with sources of LED emitters. A
typical IR detection system will use tw1o emitters. By
controlling when the emitters are active, the detection system
can determine simple directional information: Left, Right, or

There are several types of detectors for IR light. There are
photo-diodes, photo-transistors, and a couple others. Usually,
you buy IR emitter/detector pairs, which are tuned for each
other. This is recommended when buying surplus, since chances are
someone has verified they work together.

The other important detector for working with IR is a detector
module, such as the Sharp GP1U5 (also the G1U52X) module. This
module contains the IR detector and a small circuit that detects a
40khz modulation (i.e. the IR light is flashing on and off at
about 40khz). The nice part about using a modulated light is
the ability to reject noisy light signals. The world is full of
light sources. Being able to detect a certain quality of a light,
such as flashing at 40khz, means you can filter out much of the
light you don`t want.

infrared Implementing Infrared Object Detection

The components of the IR detection system

The above photo shows these parts installed on the front of a
robot. The Sharp IR detector module is the square box at the top
of the frame, and the emitters are enclosed in aluminum tubes
near the bottom.

The Schematic

To use the Sharp IR detection module, you need to have a
circuit that can flash the light at 40khz, which is 40,000 a
second (pretty fast!). This is called modulation. The circuit
that does modulation is called an oscillator, and I have shown
one below.

irschem Implementing Infrared Object Detection

A simple 40khz modulation circuit.

The above circuit is an interesting one to look at. It uses a
single 74HC04 (inverter) in several ways that you don`t normally
see, especially all at once. Lets take a quick tour.

There are three major parts to the circuit. The center (U1:A
and U1:B plus discrete components) forms a feedback oscillator.
If you follow the flow of the logic gates, you see that the
output of A is fed into the input of B, which is fed to the input
of A. Now, there is a gate propagation delay factor that
causes this circuit to continuously flip states. The important
state is the output of gate U1:B, which is fed to the driver
gates. The resistors and capacitor in the circuit are there to
regulate the frequency at which this circuit feeds back into
itself. Resistor R2 can be used to adjust the frequency of this
circuit. The Sharp detector is fairly forgiving about the exact
modulation frequency, but getting it as close as possible to
40khz is recommended. Note that the above circuit is tuned to
work with the 74HC04, and is known NOT TO WORK with the 7404,
74LS04, and other TTL versions. Do yourself a favor and get the
real thing.

The output from the oscillator is sent through tw1o buffers.
Here the gates act to isolate the oscillator section from the IR
emitter section. The buffers also act as current sources for the
IR emitters. It is important to isolate the oscillator from the
LED`s, since the timing would be affected by the particular
types of LED you use.

The final gates are the U1:C and U1:D gates. These are the
control lines that you would connect to the output ports of the
CPU. They act to buffer the CPU from the current requirements of
the LED`s.

The interface to the CPU is done through pins 5 and 9 in the
above circuit (gates C and D). These control when the emitters
turn on. The only other variable is the resistor R2, which should
only require initial adjustment to get the correct frequency.

The Detector module is simple to wire up. The connections are
to power, ground, and the output signal. The output from the
sharp detector is a digital signal.

irdetect Implementing Infrared Object Detection

Notice that R5 acts as a pull-up resistor, similar to other
digital inputs. Capacitor C1 acts as a bypass capacitor. Another
unusual connection is betw1een ground and the case. Most of the
Sharp modules are intended to be mounted on a circuit board.
It expects the case to be grounded. Be sure to make a
electrical connection betw1een ground and the case by soldering a
wire directly to the metal housing