timer555

555 Timer Project

For Part A of this summative students are required to design, build and demonstrate a 555 astable timer circuit.

There are several steps in this project as outlined below;

Step	Briefing	Activity	What to Hand In
1	Introduction to the 555 timer circuit	Select component values for your circuit and calculate the frequency and duty cycle of the oscillator.	Calculations
2	Demonstrate virtual oscilloscope.	Create a schematic and simulation of the circuit.	Print out of schematic and simulated oscilloscope trace.
3	Set up of oscilloscope.	Breadboard the circuit and connect to digital analyzer or oscilloscope.	Oscilloscope trace print out and check off breadboard.
4	Obtain parts for the circuit.	Create a PCB of the circuit and test.	PCB functioning

1.0 Introduction to the 555 timer Circuit.

Intro to 555 circuit
- how an RC timer can oscillate
  - comparator
  - voltage divider
- Monostable Operation
  - debounced switch
- Astable Operation
  - oscillator
  - period, frequency, duty cycle
- see links

Selecting component values.
- Stocked Resistor Values
- Stocked Capacitor Values

Calculating the output waveform of the 555 Timer
- Calculate the time the signal is on using the following formula;
  - th=0.693*(Ra+Rb)*C
- Calculate the time the signal is off using the following formula;
  - tl=0.693*Rb*C
- Calculate the period using the following formula;
  - T=th+tl
- Calculate the frequency using any of the following formulas;
  - F=1/T
  - F=1/[th+tl]
  - F=1/[0.693(Ra+2Rb)*C]
  - F=1.44/[(Ra+2Rb)*C]
- Link to 555 timer calculator
Reference
- 555 spec sheet

2.0 Creating a schematic and simulating the 555 timer circuit. If your simulation gives the error "time step too small" then complete the fix in "bugs "n" stuff".

3.0 Breadboarding the 555 timer circuit and testing it with an oscilloscope.

4.0Fabricating a PCB

Print mask on Blue Paper
Cut Copper
Clean copper with fine steel wool;
Laminate mask onto copper surface
Remove blue paper
Check mask trace on copper and fix with marker if required
Etch
Rinse
Remove black with course steel wool
Get specific instruction on drilling (how to and safety)
Drill PCB
Soldering
Get specific instruction on soldering (how to and safety)
Clean copper with fine steel wool
Solder in components
- items least affected by heat first
- note polarity of sockets and polarized components

Final Test
- Connect to power supply
- Disconnect immediately if;
  - it does not work as expected
  - the current draw of the power supply goes too high
  - any component gets too hot

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