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Electronics (PROCESSES (Thyristors
a thyristor can be used to create a…
Electronics
PROCESSES
Thyristors
- a thyristor can be used to create a bistable circuit, which can function as a latch
- it can drive high current outputs
- the gate acts as the trigger. It is very sensitive and will switch on for even a momentary and very small electronic signal
Op amps
- an op amp is an IC device used to amplify small differences between two input voltages
- the open loop gain of an op amp is 100000. The gain can be limited by using an input resistor and a feedback resistor
- an op amp can be used as a comparator by linking a reference voltage from a potential divider to the non-inverting input and an analogue sensor to the output
- an op amp comparator can function as an ADC if the voltage gains exceed the available power supply, such as with open loop gain
- an inverting amplifier can be created by using an input resistor and negative feedback from the output to the inverting input through a feedback resistor
OR gates
- a logic gate is a digital electronic device used to determine the state of an output based on a number of inputs
- an OR gate makes the output high when any of the inputs
is high
- an OR gate can be constructed using the 4071 IC
AND gates
- an AND gate makes the output high when both of the inputs are high
- pull down resistors are needed with logic gate ICs to prevent static electricity causing pins to float high and register a false input
- digital ICs have an upper threshold voltage above which they will recognize an input as high and a lower threshold voltage below which they will recognize an input as low. These are normally two-thirds and one-third of the supply voltage, respectively
NOT gates
- a NOT gate inverts the input signal
- the output from logic gate ICs can have the full voltage of the circuit but only low current. To operate high current devices they need to be used in combination with a transducer driver
- multiple logic gates can be used in combination to solve problems
555 IC
- a 555 IC is a digital device that can be used as part of a monostable or an astable circuit
- a monostable circuit produces a high output for a set period of time. An astable circuit produces a continuous pulsed output
- with a 9V supply a 555 IC can produce an output of 7V. To operate high current devices it needs to be used in combination with a transducer driver
Monostable circuits
- the time period of the output for a monostable circuit including a 555 IC is determined by the time constant. This is determined by the capacitor and resistor used
- a pull up resistor is used so that an input on a digital device receives the full voltage of the supply, to ensure that it registers high
Astable circuits
- an astable circuit generates pulses, and can be constructed using a 555 timer IC
- the frequency of the pulses depends upon the values of the timing resistors and capacitors
- the mark/space ratio is the ratio of the on time to the off time
Counters
- a 4017 IC has ten outputs. It produces a sequential output that can be cascaded or limited to fewer than ten outputs by linking an output to the reset
- a 4026 IC can be used with a astable pulse generator to count from 0 to 10 using a seven-segment display
- mechanical switches can be debounced by using a monostable timer set on a short time period or a Schmitt trigger
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INPUTS
Switches
- mechanical switches are available in a range of different types, such as SPST, SPDT, PTM and PTB
- the type of switch used will depend upon the job it is needed to perform
- the different types of switches are available in a wide range of forms. For example, latching SPST switches include rocker, slide and toggle types. Momentary PTM/PTB switches include buttons and microswitches
- switch bounce happens where mechanical switches do not make and maintain a 'clean' contact at the first attempt. This can interfere with the operation of some electronic circuits
Transistors
- transistors are electronic switches. They are analogue components that can be used to amplify current
- common functions of a transistor are electronic switching, sensing changes of resistance and driving high current outputs
- different transistors can be used in combination (for example as a Darlington pair) to combine high amplification with high current load
FETs
- FETs are electronic switches. They are digital components
- common functions of FETs are as transducer drivers for high current outputs from a low power process units such as integrated circuits and as electronic switches connected to high resistance/low current input sensors
Potential Dividers
- potential dividers are created from resistors in series connected across a power supply
- the voltage signal is developed across the bottom resistor R2
- variable resistors can be used to create variable voltage signals
- LDRs and thermistors can be used in a potential divider to create variable voltage signals from a potential divider. Depending upon how these components are arranged, they can be used to provide a voltage signal that increases as the sensor detects more or less light (or a colder or warmer temperature)
- replacing the series resistor used with an LDR or thermistor with a variable resistor can allow the sensitivity of the sensor to be controlled, allowing the potential divider to form part of a comparator
OUTPUTS
LEDs and displays
- an LED is a special type of diode that emits light when current flows through it in the correct direction
- LEDs must be protected by a series resistor
- a seven-segment display is an arrangement of LEDs used to show a decimal number
Relays and opto-isolators
- a relay can be used to interface teo circuits without an electrical connection or to create a latch
- relays are NO before being switched
- opto-isolators use an IR-emitting diode and a phototransistor to interface between electronic circuits
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