How flowcharts and microcontrollers (PICs) are used in control systems

• Flowcharts use symbols like 'start', 'stop', 'decision', 'compare', and 'macro' to visually represent program logic.
• Microcontrollers (PICs) are compact ICs that control inputs and outputs, used in various applications including robotics.
• Bit patterns in flowcharts represent the binary states of input and output devices, showing how microcontrollers interact with the system.
• Flowcharts help design and explain microcontroller programs, illustrating the sequence of operations and decision points.
• Amplification, using transistors, is required when output devices need more power than a microcontroller can provide.
• Microcontrollers are used in circuits with digital inputs and outputs, and these circuits can be designed and interpreted using flowcharts and bit patterns.

Flowcharts, PICs and bit patterns

Drawing and analysing flowchart diagrams involves elements like count, compare, macro, do macro, end, increments, decrements, and expressions. Microcontrollers (PICs) are used in control systems, identified by their circuit symbols, and applied in robotic control.

Bit patterns show the states of input and output devices. Circuits with digital inputs and outputs are designed and interpreted, and amplification is needed to drive certain output devices from a PIC.

Start

• start is a cell that indicates the beginning of the flowchart program
• is needed start the program

Stop

• stop is a cell that signifies the end of the flowchart
• if used, the circuit would need reset to allow the program to restart again

Output

• output is a cell that sends a signal to an output device to tell it to turn on or off
• activates devices like LEDs, buzzers, or motors

Wait

• wait is a cell that pauses the program for a specified amount of time
• delays actions to allow for timing control

Decision

• decision is a cell that makes a choice based on a condition
• directs the flowchart to different paths based on true or false conditions
• example: has a push to make (PTM) switch been pressed? Yes or no?

Compare

• compare is a cell that checks if a specific condition is met by comparing two values
• directs the flowchart based on whether the condition is true or false
• example: is the temperature being read by a thermistor above 27 degrees Celsius?

Macro

• macro is a set of instructions grouped together to perform a specific task
• simplifies the flowchart by grouping complex sequences into a sub-routine
• the macro is activated by running the do macro command in the main flowchart

Do macro

• do macro is a cell that executes the instructions defined in a macro cell
• allows the flowchart to perform grouped tasks as needed
• allows the grouped instructions in a macro to be repeated whenever needed in the main flowchart

End

• end macro is a cell that signifies the termination of the macro sub-routine running
• indicates that the process has completed all necessary actions and should return to follow the main flowchart

Count

• count is a cell that keeps track of the number of times an event occurs
• increments a counter each time the event happens
• could be used by a sensor to detect items going past on a conveyor belt

Increment

• increment is a cell that increases the value of a variable by a set amount

Decrement

• decrement is a cell that decreases the value of a variable by a set amount

Expression

• expression is a cell that performs mathematical or logical operations on variables
• calculates values or evaluates conditions within the flowchart
• can be used with devices requiring calculated inputs, like variable resistors or digital displays

Example flowchart for a simple pedestrian crossing:

1. Starts the flowchart.

2. Checks the pedestrian crossing switch to stop the cars. If pressed, red light is on for 15 seconds and checks again for switch

3. If the switch is not pressed, run amber flash macro five times.

4. Turn on the green LED for 60 seconds

5. Check if pedestrian crossing switch pressed, if not loop to keep green LED on for another 60 seconds.

6. If pressed, switch amber LED on for 3 seconds

7. Loop back to switch on the red LED for 15 seconds.

Amber flash macro

1. Macro to run amber flash sub-routine
2. Switch on amber LED
3. Wait 05 seconds
4. Switch off amber LED
5. Wait 05 seconds
6. End amber flash macro

A microcontroller is a low power (5V), compact integrated circuit (IC) designed to run a program to control a range of inputs and outputs. It combines memory, processing units, and input/output interfaces in one chip.

Uses: microcontrollers can be used for various applications, such as household appliances, alarm systems, medical devices, vehicle systems, and electronic instruments.

Sizes: microcontrollers are available in different sizes, including 8-pin, 14-pin, 18-pin, 20-pin and 28-pin versions. The size determines the number of input/output connections and the complexity of tasks it can handle.

Robotic control: in robotics, microcontrollers process sensor inputs and control actuators, enabling robots to perform tasks autonomously. They are crucial for the precise control and coordination of robotic movements.

Flowcharts: flowcharts are used to design and explain the sequence of operations in a microcontroller program. They help visualize the steps and decision points in the control process.
Other programming methods are available such as text-based programming languages (BASIC, C++ etc) or simple block-based programming editors.

Bit patterns: bit patterns in a flowchart program represent the states of input and output devices using binary (1/on or 0/off), showing how the microcontroller interacts with other components in the system by switching them on or off at particular stages.

Bit patterns:

1 = ON
0 = OFF
x = Ignore/no change

Some output devices require more power than the 5V a microcontroller can provide

Examples include:

• motors
• relays
• solenoids
• buzzers

Amplifiers, such as NPN transistors, are used to boost the signal from the microcontroller to drive these high-power devices effectively. In the circuit diagram below, a transistor is being used to amplify the signal coming from the microcontroller to make the relay energise so that it can switch on the secondary 24V lamp circuit.