Topic 5 of 6 · Form 6
Electronics and control systems
Input → process → output, with feedback in closed-loop systems.
Notes for this topic 1 file, in order
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System approach
Input → process → output, with feedback in closed-loop systems.
Components
- Inputs: switches, potential dividers with LDRs and thermistors, sensors.
- Processes: transistors (as switches – a small base current controls a larger collector current), MOSFETs, 555 timers (monostable and astable), op-amps as comparators, logic gates, microcontrollers (programmed with flowcharts or code).
- Outputs: LEDs (with series resistors), buzzers, relays (to switch high-current loads), motors and solenoids.
Calculations
- Ohm's law V = IR; power P = VI.
- Potential divider: Vout = Vin × R₂/(R₁ + R₂).
- 555 monostable time T ≈ 1.1RC.
Worked example: Find the pulse length of a 555 monostable with R = 100 kΩ and C = 100 µF.
T = 1.1 × 100 000 × 100 × 10⁻⁶ = 11 s
Applications
Automatic irrigation (soil moisture sensor), security alarms, solar charge controllers, street lighting, and temperature control in incubators – appropriate for local needs.
PCB manufacture
Circuit design software, PCB etching or milling, soldering and testing.
Exam tip: Draw circuits with standard symbols and explain the function of each block.
Check yourself
- Why is a relay used with a transistor to switch a motor?
- In a potential divider, Vin = 9 V, R₁ = 10 kΩ, R₂ = 20 kΩ. Find Vout across R₂.
- What is feedback in a control system?
Show answers
- The relay allows the small transistor current to switch a larger, separate current needed by the motor (and isolates circuits).
- 6 V
- Information from the output fed back to the input so the system can adjust (closed-loop control).
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