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Electronics - Build a System (Fantasy Carwash)

Extracts from this document...


Rassel M Akthar 11H



Electronics Coursework


Statement of Problem

The Car wash is using too much water to wash each car, so I will design a system which triggers the motor to pump water out for 20 seconds then stops.



The will be a pressure pad on the floor and when it is pressed it triggers the monostable, the motor turns from a logic 0 to 1. The Motor runs for 20 seconds and then is triggered off by the monostable, the car may then exit.


Alternative solution

Instead of a drive through carwash the customer can wash their car themselves by using the help yourself machine.  image19.png

...read more.


Pressure sensor


I want my system to have a pressure sensor as an input so when a car rides over it, the output gives a logic 1 signal and triggers the monostable which holds the motor on for 20 seconds.

Circuit Diagram

Instead of using a pressure sensor I used a push to make switch to test it.image20.png

To test the pressure sensor I put a voltmeter on either side of the resister.

(To make the pressure sensor on you put the switch on)


When switch opens voltmeter reads 0 V

When switch is pressed voltmeter reads 5.71 V


The pressure sensor subsystem worked as I expected so it can be used for my final system circuit.

Main Switch


The system will have a main switch that has to be on for the system to work. When switch is closed voltage should be high and when it is open then voltage should be low.

Circuit Diagram

...read more.


Circuit Diagram



1                                                                2                        


Diagram 1 is the circuit I tried first but I had a problem, the motor didn’t get enough current to operate. So I looked through the book called “A Practical Approach To Systems Electronic” and found a solution to this problem, instead of just one transistor I used a Darlington Pair which gave the motor enough current to operate.


The Motor worked as specification required.


When both inputs are high in the And Gate, it triggers the monostable which latches the motor on for 20 seconds and then motor switches off.

The Darlington pair boosts the motor current so it has enough current to operate.

Circuit Diagram



The motor comes on for approximately 20 seconds when both inputs are pressed, and then turns off.


The full system works exactly as expected.

Components cost list:

2 * Push to make switch:

And Gate:

555 Timer:

Darlington Pair:

2 * 10K resister:

820K resister:

47uF Capacitor:

2 * 1K resister:

100 ohm resister:

22 ohm resister:


Sources of Information

“A Practical Approach To Systems Electronics”

...read more.

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