1. Time Delay
   1. Monostable
      1. 555
      2. Controlled with Resistor
      3. Controlled with capacitor
      4. T = R x C
      5. Contains a switch
2. Pulse
   1. Astable
      1. 555
      2. Controlled by 2 resistors
      3. Contolled by 1 capacitor
      4. Rate of pulse measured in Hz.
      5. Calculated by--
3. Decade Counter (4017)
   1. Counts 0 to 9.
   2. Moves on one count when power applied to pin 14
      1. Use an monostable for this
   3. Can be used to flash the 10 leds if fitted to the astable
4. Potential Divider
   1. Two resistors stretch between 0 and 9 volts.
   2. One is replaced with a sensor e.g. LDR.
   3. Gives an analogue output.
5. PIC Microcontroller
   1. Uses a range of differant sized IC's.
   2. Programmed using a PC
   3. Requires a download circuit
   4. requires a voltage regulator to reduce voltage to 5.5v
6. Transistor
   1. Amplifies the voltage
      1. requires only 0.7 to turn on.
   2. Is a switch