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LDR Based Object Counter

Circuit shown below is used to count objects by sensing light blocked by obstacle which is detected by LDR(Light Emitting Resistor).

Fig: Circuit Schematic Using Eagle.

Components Used:

  • LDR
  • Resistors(R16-100K, R17-330 ohm, R11-47k, R12-100K, R10-330 ohm, Resistors used for 7 segment display are al 330 ohm)
  • Capacitors(C1-10uF,C2-10uF,R15-0.01uF)
  • LED
  • 555 Timer ICs
  • IC 7490 
  • IC 7447 
  • 7 Segment display

IC 555 Timer:

   First 555 IC is configured in monostable mode.Monostable circuit is dark sensor circuit,whose output is given to second 555 IC which is configured in astable  mode.here pin 3 of monistable is connected to the pin 4 of astable circuit.When output from monostable is given to astable ,astable starts giving pulses to the counter 7490.Frequency for counter module is set up using R4,R3 and C2.

IC 7490 Decade Counter:

   7490 decade counter will give 4-bit output in binary at pins-12,9,8,11. Pins 12,9,8,11 are connected to the pins 7,1,2,6  of IC 7447.7490 have 4 flip-flops and 2 resets.As will need mod-10 counter so there is no need to use resets and resets will be connected to the ground (i.e. pins 2,3,6,7 of 7490 are connected to the ground) to make them deactivated.
If we connect Qa to input B that is we cascade mod 2 and mod 5 to get mod 10 counter shown in the figure below.
Fig: Block Diagram of 7490




IC 7447-BCD to Seven Segment Display:

IC 7447 gets the Binary Coded decimal as input as well as gives the output like the related Seven Segment Code.

Fig: IC 7447 decoder to Seven Segment Display.


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