# Moving Car Transit

#### vsclassic

Joined Dec 15, 2010
2
Hello all,

I have a school project assignment where we are supposed to design a car that passes through stations and upon a passing through a selected number of stations, the car will automatically reverse.
the car must be able to count the number of stations it passes on a HEX display and also count down when it reverses.
the car must be able to stop upon hitting an emergency button in both directions

we are provided with the following:

1) 74LS32 OR gate
2) 74LS08 AND gate
3) 74LS04 NOT gate
4) 74LS02 NOR gate
5) 74LS00 NAND gate
6) 74LS74 D flip flop
7) 2N3904 NPN transistor

Light Dependent Sensor Circuit

Counter and Display Circuit

Motion Control Circuit

Count Limiting Circuit (Need help with this!)

I have already done the circuits above, all that is left is to create a count limiting circuit board that controls the count, whether the car moves forward or backward, basically it is the brain of the car.

Appreciate any help rendered!
Thanks!

#### John P

Joined Oct 14, 2008
1,781
Did you design those modules, or did the instructor provide them? Because I think you've got a serious design issue with the counter: how are you ever going to set it to count any particular number? The diagram shows the inputs to the counter as unconnected, which they definitely should not be. You haven't said what you're allowed to use in the way of switches and resistors and capacitors.

Solve the counter problem, and the rest of it looks pretty simple. Oh, you need to consider not just an emergency stop switch, but how you're going to end the emergency condition. Are you allowed to have two buttons, so there can be a "restart"? And should the logic always be in the "stop" condition when power is first switched on?

#### vsclassic

Joined Dec 15, 2010
2

Those modules are provided by the instructor, we are to solder them onto the board, which i have already done. the Count limiting circuit is to be designed by ourselves.

-->how are you ever going to set it to count any particular number?
The LDR sensor will produce a logic one output whenever it passes under the station from J3. The Count limiting circuit will pass this signal to Third junction of the Counter which connects to the "UP" of the 74LS193.

We are allowed to use switches, resistors, capacitors, Logic gates, transistors.

Regarding the emergency stop switch, it works like the relay in the motion control circuit. the relay is attached to the edges of the car such that when in contact with a wall, the relay is pressed down causing the car to stop moving. the car will move when the relay springs back up.

As for should the logic always be in the "stop" condition when power is first switched on?
It doesn't need to be in the "stop" condition.

I have came up with a circuit with a digital comparator to detect the signal from the counter and match it with the desired signal input. when the signal matches, should the output produce a Logic high?

#### Eduke

Joined Dec 17, 2010
1
hi...im working on this too n i need help...is the circuit u posted working?