Subsystem: IP3

Task Title:
L.E.D. Control
Switch Triggers
(- ive going)

Introduction and Aims

We will be using the I/P 3 subsystem to produce a negative going voltage. This follows on from the previous task when we used I/P 2's push switch to produce a positive voltage. We will now be sinking the next module and using an L.E.D. (see OP1) as the output of our system.

Before the switch is pressed, we will show how I/P 3's 10K "pull up" resistor (opposite of "pull-down"), takes the negative (cathode) side of the L.E.D. up to the positive power rail. This can be very useful when connecting to logic/digital circuits as they need to see either a low (pulled down) or high (pulled up) signal.



SubSystem Circuit and Block Diagram

 

IP3
-Going Switch
 
OP1
Sinked
L.E.D.
 

 


Investigating the System

Open the "Library of Subsystems" here and search "IP3 Sinking Inputs". Read the description and then complete the following:-

1, The Resistor labelled R1 should have a value of Ohms.

2, When the switch is pressed the LED will

3, When pressed, the voltage at the top of the switch is volts and the LED is being "sinked".

4, The 470 Ohm resistor connected in series with the LED is there to limit the flowing through the LED.

Modelling the above System/Circuit

There are different ways to model and test circuits before components are soldered to a P.C.B. Modelling is an important stage as it helps you spot any problems and make modifications easily.

Method 1: Breadboard

Using this method, components are pushed into the interconnected holes as shown in the diagram below. The lines shown indicate which holes are internally connected.

Copy and paste this image into your notes and by using the circuit diagram above, design the breadboard layout for this system.

Method 2: Computer Simulation

To begin, you will need to ask your supervisor which simulation software is available on your PC. This method allows you to build up your circuits quickly and cheaply in a virtual environment. Remember though, it will not give you hands-on experience of the components you will be using when finally soldering your PCB.

Method 3: Using OnTrack modelling hardware

See IP3 project guide.