Laser Pointer Remote Control Circuit

  
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The laser-pointer detection circuitry is able to determine when a laser light is aimed at a particular photosensor. If the laser is aimed at the top sensor, the comparator chip outputs on . If the laser is aimed at the bottom sensor, the comparator chip outputs off . The circuit could be considered complete if you wanted somethi
Laser Pointer Remote Control Circuit - schematic

ng to be turned on only while the laser is aimed at the on sensor. However, if you want the circuit to remember whether the on  sensor or the off  sensor was most recently selected, then you`re going to need to hook those outputs to a memory chip. Looking back at the schematic, you`ll notice that the output names of on  and off  have little lines above the words. Usually an output is high (5V) when a condition is true, but the line above the word means the output is low (0V) when the condition is true. The line stands for opposite , not , or negate . The reason that the comparator has been wired to do this is because the memory chip on this page needs the information in that format. However, should you have a circuit that needs normal outputs, simple swap IC1 pin 5 with IC1 pin 6, and IC1 pin 2 with IC1 pin 3. Flipping the input pins on the comparator provides the opposite output. This circuit only needs to remember whether the final output should be on (5V) or off (0V). This is the smallest, most rudimentary amount of memory. It is called a bit ; which stands for binary digit . A bit can only be on or off. The 7474 chip is a basic logic chip that contains a 1-bit memory cell. For convenience, just like the comparator chip on the previous page, the 7474 includes two independent copies of this feature on a single chip. Therefore, the 7474 has two independent 1-bit memories on the chip. We only need one bit for this...



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