R.Winter 2009

To cover the theory of 555 timer circuits – monostable and astable, operations, components and calculations

To teach the skill of designing a circuit schematic from basic components

To understand how to test a circuit idea effectivley using breadboard.

To learn how to design compact PCB’s

To learn the ‘photo etch’ method of producing circuit boards.

To recap the process of preparing and populating a circuit board

To understand WHAT an integrated circuit is, and know how to correctly number the pins on one.

To have built the 2 circuit diagrams shown later in this slideshow using circuit wizard software

To have tested these 2 circuits to ensure they work.

To be able to answer the questions about the 2 circuits on your question sheet.

To be able to explain WHICH two components affect the time delay in a timer circuit and WHY.

An integrated circuit is a collection of miniature components such as resistors, diodes, transistors assembled together into a working circuit and squeezed into a tiny space.

In the 555 timer chip you are using today there are around 40 different miniature components

The actual circuit is only a tiny part of the case – the case is big so that human hands can pick it up!

Hence goods that don’t need to be hand soldered can be MUCH smaller still!

There are 1000’s of types of Integrated circuit that do a whole range of different jobs – from counting and addition, to timing and measuring

Gather the following components:

• 9v power supply

• 555 timer I.C

• Red LED

• 1 x 330 ohm resistors

• 2 x 10k resistor

• 1 x 1000uf Electrolytic capacitor

• 1 x PTM (push to make switch)

Make the following connections, in the exact order written below:

Join pins 4 and 8 of the timer chip to the positive end of the power supply

Join pin 1 to the negative end of the power supply

Join one end of a 10K resistor to the positive end of the power supply, and join its other end to a PTM switch

Join the other end of the PTM switch to negative.

Join a 10k resistor to positive, and the other end of the resistor to the positive end of the electrolytic capacitor – join the other end of the capacitor to negative

Join pins 7 and 6 of the 555 chip to the junction where the 10K resistor meets the positive end of the capacitor

Make a connection between pin 2 and the junction between the other 10K resistor and the PTM switch.

Join a 330 ohm resistor to pin 3 of the 555 timer and join the other end of the resistor to the positive end of the red LED.

Join the other end of the LED to negative and test it out by running the simulation and pressing the PTM switch. – If correct, the red LED should light for 10 seconds after you press the PTM switch.

Build the following circuit as shown below (pay attention the values of the resistors and capacitor)

Try and Answer the questions on your worksheet about the Astable circuit