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Object counter using 8051 microcontroller.
This article is about a simple object counter/visitor counter using 8051 microcontroller . AT89S51 belonging to the 8051 family is the microcontroller used here. This circuit can count the number of objects passing across a line , number of persons passing through a gate/door and so on. The can be simply divided into two sections i.e. the sensor section and the display section.
Sensor.
The sensor part consists of a ultra bright led (with focus), and LDR, opamp LM324 and the associated passive components. The LED is placed on one side of the door and the LDR is placed on the other side so that the light from the LED falls directly on the LDR.As you know, the resistance of the LDR has an inverse relationship with the intensity of the light falling on it. The preset resistor R14 is so adjusted that the voltage across the LDR is below 1.5V when it is illuminated. This voltage (labelled A in the circuit diagram) is connected to the inverting input of the opamp which is wired as a comparator with reference voltage 1.5V (set using R15 and R16).Capacitor C1 is meant for bypassing noise or anything like that which may cause false triggering.Resistor R13 is meant to control the current through the LED.
When the light is falling on the LDR the voltage across it will be less than the reference voltage and so the output of the opamp remains high. When the light beam is interrupted, the voltage across the LDR goes above the reference voltage and so the opamp output goes low and it indicates a pass.
Display section.
The output of the opamp is fed to the INTO (interrupt 0) pin of the microcontroller. The microcontroller is programmed to count the number of negative edge pulses received at the INT0 pin and displays it on the three digit seven segment display.
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Abstract
We need following components for making an object counter
1. 555- configured in monostable mode(automatic dark sensor using 555)
2. 555- configured in Astable mode
3. 7490- decade counter- Click here to get the datasheet
4. 7447- BCD to seven segment display- Click here to get the datasheet.
5. Seven segment display- Common Anode
Here, CC-Common Cathode and CA-Common Anode.
6. Resistors- see the schematic
7. Capacitors- see the schematic
8. Light dependent resistor (LDR)
9. LED
10. Power supply
There are basically three modules in object counter:
555 timer configured in monostable mode.
555 timer configured in astable mode.
Counter module.
555 timer configured in monostable mode is a simple automatic dark sensor circuit that gives output when light falling on LDR is blocked. Pin 3 of monostable circuit has been connected to pin 4 of astable timer. When monostable circuit generates output, astable mode timer starts giving pulses to the counter module.
Frequency for counter module is set up using R4, R3 and C2.
7490 acts as a decade counter and 7447 uses the output of 7490 to display numbers on seven segment display.
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Object-oriented databases make the promise of reduced maintenance, code reusability, real world modeling, and improved reliability and flexibility. However, these are just promises and in the real world some users find that the object-oriented benefits are not as compelling as they originally believed. For example, what is code reusability? Some will say that they can reuse much of the object-oriented code that is created for a system, but many say there is no more code reusability in object-oriented systems than in traditional systems. Code reusability is a subjective thing, and depends heavily on how the system is defined.
