Discovering Electronics 1-3 Flashcards
What are the three main sections of an electronic system?
Input sensors, signal processing, and output devices
What is the function of input sensing units in an electronic system?
They convert non-electrical signals (e.g., light, temperature) into electrical form
What are the two types of input sensing units?
Digital type and analogue type
What is the difference between digital and analogue signals?
Digital signals can only have two values (0V or +5V), while analogue signals can vary between 0V and +5V
When is a voltage point considered LOW?
When it is near the 0V line, typically less than 2 volts
When is a voltage point considered HIGH?
When it is near the positive line, typically greater than 3 volts
What is the function of a switch unit?
Detects pressure; output signal goes high when pressed
What is the function of a light sensing unit?
Detects light; output signal increases as light level increases
What is the function of a temperature sensor?
Detects temperature; output signal increases as temperature rises
What is the function of a reed/magnetic switch?
Detects magnetic field; output signal goes high when a magnet is near
What is the function of a pulse generator unit?
Generates continuous stream of pulses; pulse frequency increases as control is turned clockwise
What is the purpose of output devices in an electronic system?
They convert electrical signals into other forms of energy (light, sound, motion)
What is the function of a lamp unit?
Converts electrical signal into light
What is the function of a buzzer unit?
Converts electrical signal into sound
What is the function of a motor unit?
Converts electrical signal into rotational motion
What is the function of a solenoid unit?
Converts electrical signal into linear motion
Why are transducer drivers needed in electronic systems?
Most input sensing units cannot supply sufficient current to directly drive output devices
What are the two types of drivers mentioned in the text?
Transducer Driver unit (with MOSFET) and Transistor Switch unit (with NPN transistor)
Which driver is capable of supplying several amps to an output device?
Transducer Driver (MOSFET)
What is a logic gate?
A decision-making unit within electronic systems (digital processing unit)
What are the three basic logic gates covered in the chapter?
AND gate, OR gate, and NOT gate (inverter)
What is the action of an AND gate?
Output signal goes high only when both input signals are high
What is the action of an OR gate?
Output signal goes high when either one or both input signals are high
What is the action of a NOT gate (inverter)?
Reverses the digital input signal; output goes low when input is high and vice versa
What is the purpose of a delay unit?
Provides a time delay; output signal goes high for a preset time period
What is the purpose of a latch unit?
When input signal goes high, output signal goes high and stays high until reset
What is the purpose of a comparator unit?
Compares input signal with reference voltage; output is high if input is larger than reference
Why would you use a comparator unit?
To convert an analogue input signal into a digital output signal and improve sensitivity when only small changes occur
What are the steps to consider when designing an electronic system?
1) Decide input units, 2) Decide output units, 3) Decide processing units, 4) Draw block diagram, 5) Set up and test, 6) Make changes if needed
What problem might occur when using a light sensor to detect darkness?
The light sensor detects light (not darkness), so a NOT gate (inverter) is needed to invert the signal
What is a practical application of a delay unit?
An external security light that stays on for a set time after being triggered
What is a practical application of a latch unit?
A burglar alarm that stays on until manually reset
How can you represent voltage changes in a digital system?
With symbols showing voltage rising or falling instantly
How can you represent voltage changes in an analogue system?
With symbols showing voltage rising or falling gradually
What is a block diagram?
A visual representation of a system showing the connections between subsystems
What is the function of a moisture sensor?
Detects moisture; output signal increases as moisture level increases
What is the function of a sound sensor?
Detects noise; output signal increases as noise level increases
What is the function of an LED unit?
Converts electrical signal into light (similar to lamp unit but more efficient)
What is a subsystem in an electronic context?
Building blocks that make up a complete system, each performing a definite function
What is the purpose of a signal processing section in an electronic system?
To process and modify electrical signals between input and output
What is electric current?
The flow of electrons through a conductor in one direction
What unit is current measured in?
Amperes (amps or A)
How do ammeters connect in a circuit?
In series (breaking the circuit and connecting in the gap)
What is 1 mA equal to in amperes?
0.001 A (1/1000 of an amp)
What is 1 μA equal to in amperes?
0.000001 A (1/1000000 of an amp)
What is the current rule for series circuits?
Current is the same at all points in a series circuit
What is the current rule for parallel circuits?
Current splits at junctions and recombines later (sum of currents entering a junction equals sum of currents leaving)
What are the best electrical conductors?
Silver
What are common electrical insulators?
Polythene and PVC (polyvinyl chloride)
What are semiconductors?
Materials like silicon and germanium that conduct to a certain extent
What is voltage?
The electrical pressure or force that causes current to flow in a circuit
What unit is voltage measured in?
Volts (V)
How do voltmeters connect in a circuit?
In parallel (across the component)
What is 1 mV equal to in volts?
0.001 V (1/1000 of a volt)
What is the voltage rule for series circuits?
The sum of voltages across components equals the supply voltage
What is the voltage rule for parallel circuits?
Voltage is the same across all components in parallel
What happens to voltage in cells connected in series?
It adds up (if connected positive to negative)
What is resistance?
Opposition to the flow of electric current
What unit is resistance measured in?
Ohms (Ω)
What is the formula for calculating resistance?
R = V/I (resistance equals voltage divided by current)
What is Ohm’s Law?
V = I × R (voltage equals current multiplied by resistance)
What is 1 kΩ equal to in ohms?
1000 Ω (1 thousand ohms)
What is 1 MΩ equal to in ohms?
1000000 Ω (1 million ohms)
What is the purpose of resistors in circuits?
To limit current to a desired value
What happens to current when resistance increases?
Current decreases
In a parallel circuit
which branch has more current?
What is a voltage divider circuit?
Two resistors connected in series across a voltage source to create a lower output voltage
What is the voltage divider rule formula?
Vout = (R2/(R1+R2)) × Vin
What happens in a voltage divider with equal resistors?
The voltage is divided equally (half across each resistor)
What does the I-V characteristic of a resistor look like?
A straight line (constant resistance)
What does the I-V characteristic of a filament lamp look like?
A curve that becomes less steep (resistance increases with current due to heating)
What does the I-V characteristic of a silicon diode look like?
No current for negative voltages
What is electrical power?
The rate at which energy is used or transferred
What unit is power measured in?
Watts (W)
What is the basic formula for electrical power?
P = V × I (power equals voltage multiplied by current)
What are two alternative formulas for power in resistors?
P = I² × R and P = V²/R
What is the formula for energy transfer?
E = P × t (energy equals power multiplied by time)
What unit is energy measured in?
Joules (J)
What happens to power in a circuit when voltage doubles but resistance stays the same?
Power quadruples (P = V²/R)
What happens to power in a circuit when current doubles but resistance stays the same?
Power quadruples (P = I² × R)
What is the symbol for a fixed resistor?
A rectangle (or zigzag line in some regions)
What is the symbol for a variable resistor?
A rectangle with an arrow through it (or zigzag with arrow)
What is the symbol for a light dependent resistor (LDR)?
A resistor symbol with two diagonal arrows pointing inward
What is the symbol for a thermistor?
A resistor symbol with a diagonal line through it or with a T
What is the symbol for an LED?
A diode symbol with two arrows pointing outward
What is the symbol for a cell?
A long and short parallel line
What is the symbol for a battery?
Multiple cell symbols in series
What is the symbol for an ammeter?
A circle with letter A inside
What is the symbol for a voltmeter?
A circle with letter V inside
How is voltage at a point measured in circuits?
With respect to a reference point (usually the 0V rail)
What is the formula for total resistance in series circuits?
R_total = R1 + R2 + R3 + …
What is the formula for two resistors in parallel?
R_total = (R1 × R2) / (R1 + R2)
How does the E24 series work?
24 standardized values per decade (e.g., 10,11,12,13,15…) with ~10% increments
What does a gold band indicate in resistor color coding?
±5% tolerance
What happens if you exceed a resistor’s power rating?
It may overheat and fail
What is the purpose of a voltage divider?
To split input voltage proportionally based on resistor ratios
How to calculate a current-limiting resistor for a 2V LED on 5V supply at 10mA?
R = (5V-2V)/0.01A = 300Ω
What happens to LDR resistance in bright light?
Decreases significantly (e.g., from MΩ to kΩ)
What is the symbol for an NTC thermistor?
Symbol with -t° indicator
How does an NTC thermistor behave with temperature?
Resistance decreases as temperature increases
What is a preset resistor?
A small potentiometer adjusted with a screwdriver, then sealed
Where are reed switches commonly used?
Burglar alarms (door/window sensors)
How does a tilt switch work?
Mercury completes circuit when vertical, breaks when horizontal
What are the two potentiometer configurations?
1) Variable resistor (2 terminals) 2) Voltage divider (3 terminals)
Why can’t you directly connect a lamp to a sensing circuit?
It ‘loads’ the divider, causing voltage drop (Rule: Load R > 10× divider R)
What is typical LED current range?
10-20 mA (varies by type)
Why are LEDs more efficient than filament lamps?
No heating loss, 100,000+ hour lifespan
Calculate resistor for blue LED (3.2V) at 15mA on 9V supply
(9V-3.2V)/0.015A = 387Ω → 390Ω (E24)
What happens if you reverse-bias an LED >5V?
Permanent damage
What’s the voltage drop across a green LED?
~2.9V
How to identify LED anode?
Longer lead or flat side on casing
What sensor gives increasing voltage with rising temperature?
Thermistor at top of voltage divider
What happens to LDR output voltage in darkness?
Increases if LDR is bottom resistor
What’s the resistance range of ORP12 LDR?
Several MΩ (dark) to ~1kΩ (bright light)
Why are thermistor packages different sizes?
Response time - smaller = faster
What are the three terminals on a microswitch?
COM (common), N/O (normally open), N/C (normally closed)
How to make a 0-12V adjustable supply?
Potentiometer as voltage divider across 12V
What resistor would dim an LED safely?
Higher value than calculated (reduces current)
What happens if you use 39Ω instead of 43Ω for a lamp?
Brighter but shorter lifespan
What sensor detects door openings?
Reed switch + magnet
What component protects LEDs from overcurrent?
Series current-limiting resistor
