electronics

• Power equation


  P=IV

  P=I2R

  P=V2/I
• millifarad(mF)


  1000
• microfarad(nF)


  1,000,000
• nanofarad(μF)


  1,000,000,000
• Astable circuit


  A circuit which is not stable and continuously switches from one state to another. legs 6 and 2 must join together
• Monostable circuit


  Allows the output component to be switched on or off for a period of time. The monostable timer always returns to its original state after the time period
• Ohms law


  V=IR
• Resistors in series


  R1+R2+R3 = Rt
• Resistors in parallel


  :

  
• Voltage divider equation


  Vout = vin (R2/ R1+R2)
• LDR


  The resistance varies due to the amount of light energy falls onto the component
• Thermistor


  The resistance varies due to the amount of heat energy falls onto the component
• Transistor


  Trigger voltage 0.7V

  
• transistor gainequation


  hfe = Ic/Ib
• Darlington pair


  Can give high gain and high output

  Trigger voltage now 1.4V

  
• Thyristor


  A semiconductor that can be used to latch on to an output.

  
• Ceramic capacitator


  non-polarised

  Used for electronic equipment

  High capacity

  Low price
• Polyester capacitator


  Suitable for timer circuits

  Good quality

  Can handle high currents
• electrolytic capacitors


  They have a positive and negative lead which must be positioned i the circuit the right way round

  They have a much higher capacitance than non electrolytic capacitors
• Relays


  A relay is an electrically operated switch which uses an electromagnetic coil to move the poles of a switch when powered

  
• Diodes and back EMF

  A diode will only allow electricity to flow in one direction. This is primarily seen in circuits with components with electromagnetic coils in them such as relays and motors. This will protect the circuit from spikes of electrical current which the coil might produce
• Comparator


  An electronic device that is used to amplify voltage. A comparator compares two input voltages and outputs a binary signal indicating which is larger. If the non-inverting (+) input is greater than the inverting (-) input, the output goes high. If the inverting input is greater than the non-inverting, the output goes low.
• Not gate

  .

  
• Or gate

  
• And gate

  
• Nor gate

  
• Nand gate

  
• Xor gate


  Only is represented as 1 or "high" when only 1 of the inputs is "high or 1

  
• Pull up resistor


  When the switch is opened the input is connected to a high voltage. When the switch is closed the voltage will still drop giving a low signal
• Pull down resistor


  Used when you need to input a high signal the resistor is used to tie the input to 0 volts when the switch is opened
• Monostable time equation


  $t =$$1.1 *$$R*$$C$
• Astable time equation


  $t =$$1.44/(R1+2R2)*$$C$
• Threshold pin (6)

  
  

  When the voltage at the threshold pin reaches 2/3 of the supply voltage the timing cycle ends and the output on pin 3 goes low.
• Reset pin (4)


  Resets the timers operation
• Trigger pin (2)


  When the voltage supplied to the trigger drops below 1/3 of the supply voltage, the output goes ‘high’ or turns on.
• Discharge pin (7)


  The voltage on this pin is controlled by the internal circuit of the 555 timer. When this pin is high the timing capacitor charges; when the timer brings it low, the timing capacitor discharges
• PIC advantage


  fewer components are required as one of the voltage dividers would not be required in a programmable system. Therefore a smaller resultant circuit.
• PIC disadvantage


  comparators have a greater sensitivity to small changes in input voltages compared to PIC inputs.
• Collector current equation


  Ic = Vs/RL
• Emitter current equation


  Ie = Ib + Ic