Recently on a business trip to customers there do the equipment debugging, field as shown above, in which I was responsible for the technical section contains a drop. monitoring function, the principle of hardware is simpler, launch board array infrared emission, launch in scanning way, the launch of the signal receiving plate, the board is as follows:
Found in transmitting and receiving customer function is abnormal, trial and error, there are often the object fell but is not infrared sensing, later found to be due to install the distance is bigger than my design and validation, customers on the other side of the distance to more than one meter, the scene with a multimeter test launch unexpectedly has no reaction, the reception site nor oscilloscope, also good colleague with USB oscilloscope and notebook computers, the detect more than one meter installation distance of infrared emission signal goes like this:
Only about 120 millivolts, amplitude of the probe is used as the attenuation of 10 times the figure of X10 gear, using a LOTO OSC802, more than 100 millivolt voltage not drive the subsequent circuit of the transistor's base, found the reason, after receiving the nearer the distance, the higher the voltage value of the signal, I design and test is a few centimeters of distance, just can drive subsequent triode, install the relatively far distance, voltage amplitude is not enough, on hand only found a LM293 voltage comparator, then fly line up, to turn the small value of the signal into a 5 v of large signal amplitude,
Principle as shown in the figure below, because the distance in A place about 1 meter 120 millivolt voltage signal, through the comparison of the comparator output to the large amplitude of the signal, B
Using OSC802 oscilloscope detect after the comparator, signal more specification, and amplitude reached around 5 V, as shown in the figure below, the following figure, USB oscilloscope is also used the X10 gear up to 10 times attenuation measurement, so the measured is about 0.5 V
So the problem is solved, the test found that temporary employ the way of the comparator, not only solved the problem quickly, even not only 1 meter distance not leak, 120 cm, set up 140 cm are no problem,
As shown in the figure below, is shown in yellow circle object shade, the corresponding LED lights become red, shining is green,
