well i think i should explain it again.
its like that there is a capacity of 10 cars in the lot.now if a car enters the lot the capacity is 9.but if the car leaves the capacity is 10 again.I have to make this thing.
Look at a CD40110. One will count up or down 0 - 9. To count to 10, you'll need two cascaded together.
It has a separate up and down counter input and can be hooked up directly to a 7-segment display. You'll have to figure out a good sensor to pulse the up or down counter when a car enters or leaves.
How do you plan to determine when a car is leaving and entering the lot? If there is one dedicated entrance (cars can only enter and not leave through it) and if there is only one dedicated exit (cars can only leave, not enter), then you're set.
If there is only one lane that serves both entrance and exit, then you can use two sensors spaced some distance apart at entrance. If sensor closest to street is tripped first, then a car is entering. If the sensor closest to the parking lot is tripped first, then a car is exiting. You'll need to come up with the logic to determine which sensor is tripped first - because both with eventually be tripped by a car either coming or going - then figure out how to send a count up or count down signal to the CD40110.
If there is one double lane (cars enter and exit through the same entrance simultaneously), things get more interesting . . .
And please write out your responses (words) fully, it takes some of us (eh-hem, me) a lot of time trying to decipher what you wrote.
sorry for that
i will try that it does not happen again.
and if i make one entrance door and a separate door for exit.and what if i dnt want to use sensors.
Georacer is right, you need something to send a signal to your circuit to indicate when a car enters or leaves the lot. If you have one dedicated entrance and one dedicated exit, you need two sensors, one for each.
Understand the term sensor is generic. A sensor could be IR beam, a pressure sensor, or even something as simple as a switch.
If your parking lot has one entrance and one exit, you could have a gate at both locations as you find in parking garages and airport lots. A car pulls up to the entrance, stops at the gate, pushes a button to open the gate (and often to get a time-stamped ticket so the lot can charge the driver for the time the car is parked). If you have this gate, you can use the signal from the button being pushed as a count pulse to your circuit. Same for the exit - car pulls up to exit, presses button to exit, gate lifts, etc.
You can add a light (or vacant sign) at the entrance telling drivers when the lot has space available and when it is full.
Another automatic option is to have two sensors in the common entrance/exit. Sensor A will be towards the exterior of the garage and sensor B towards the inside.
The system starts at an initial state. When sensor A is tripped the system goes to a state where it waits for the sensor B to activate. After that happens, it will increase the count by one and return to the initial state.
Same for B first, but the count will be decreased.
In order to discuss further about implementation, we need you to tell us which counter will you use, as it will affect the signals it needs to perform the up/down count.