Exercise - Creating a Flowchart

The task is to produce a Flowcode flowchart that lights a lamp for ten seconds when a switch is pressed.
Although it may not be realistic to use a microcontroller in such a straight-forward application, it illustrates the technique of producing a Flowcode program.
The program itself may form part of a bigger program.

Formulate the sequence

The flowchart sequence will be:

Check if the switch is pressed.

If it isn't, go back to the beginning.

If it is:

switch on the lamp;

wait for 10 seconds;

switch off the lamp;

go back to the beginning.

It takes such a short time for the microcontroller to carry this out, that we don't need to worry whether the switch latches on or not.

Set up the flowchart

• Open Flowcode.
• On the Startup screen, click on 'New embedded project'.

The Project Options dialogue box opens.

(Click on the link for a full explanation of all the options available.)

• Accept the default settings by clicking on 'OK'.

An empty flowchart window opens, which may contain other items such as a System Panel, Dashboard Panel, Properties Panel etc.

These can be revealed or hidden using the View menu.

• Set up the flowchart window so that you can see the System Panel and the Properties Panel.

The flowchart window should resemble the one shown below (depending on the configuration.)

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The System Panel and Properties Panel can be moved by 'clicking and dragging the title bar at the top of each panel.

Set up the input

More information about the icons used in this flowchart can be found in Icon Properties.

• Drag and drop a 'Loop' icon between the BEGIN and END icons.

The 'Loop' icon makes the microcontroller repeatedly run through the program, (though the icon can be configured to limit the number of times this happens.)

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• Inside the loop, drag and drop an 'Input' icon from the Icons toolbar.

• Double click on the icon.

This opens the 'Properties: Input' dialogue box, allowing you to configure the way the program treats information from the switch.

This information will be contained in a variable called 'switch'.

• Click on the down arrow at the right-hand end of the 'Variable:' box to open the variables dialogue box.

• Hover to the left of the 'Variables' label and click on the down arrow that appears.
• Click on the 'Add new' option to open the 'Create a New Variable' dialogue box.
• Create a new variable named "switch" with initial value "0" and description "Copies the state of the switch"

• Leave the 'Variable type:' as 'Byte'.

(For more information about variables, see Creating Variables and Variable Types.

(The resulting dialogue box is shown opposite.)

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• Finish configuring the input properties as follows:

• Change the 'Display name:' to "Read the switch".
• In the 'Variable:' box, type the name of the variable you created "switch".
• Leave the 'Port:' as PORT A.
• Select to 'Input from:' 'Single Bit' and choose bit 0.

(The resulting dialogue box is shown opposite.)

Set up like this, the program monitors the state of the switch, which will be connected to bit 0 of Port A of the microcontroller.

When the program looks at the input switch if it is pressed, the variable 'switch' contains logic 1. If unpressed, it contains logic 0.

Check the switch

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• Drag and drop a 'Decision' icon after the 'Input' icon.

• Double click on it to open the configuration dialogue box, and then:

• Rename it "Switch pressed?".
• In the 'If:' box, type "switch=1".
• Leave the 'Swap Yes and No' box unchecked.
• Click on 'OK'.

This icon makes the program perform what is known as a conditional branch.

The subsequent course of the program depends on the outcome of the condition specified in the 'Decision' icon.

In this case, it depends on whether or not the variable 'switch' = 1.

If it is, the program follows the 'Yes' route. If not, it follows the 'No' route.

Control the lamp

The 'No' branchis easy to set up. All we want is that the program returns to the beginning (taken care of by the 'Loop' icon.)

No further configuration is needed.

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Next we concentrate on the 'Yes' branch.

• Drag and drop an 'Output' icon in the 'Yes' branch.

• Double click on it to open the configuration dialogue box, and then:

• Change the 'Display name:' to "Switch on".
• In the 'Variable or value:' box, type value "1".
• Change the 'Port:' to PORT B.
• Select to 'Output to: 'Single Bit' and choose bit 0.
• Click on 'OK'.

(The resulting dialogue box is shown opposite.)

The effect of this icon is to send a logic 1 signal (high voltage) to the lamp, connected to Port B, bit 0 of the microcontroller.

This turns on the lamp.

Now, we tackle the requirement that it stays on for ten seconds and then goes off.

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• Drag and drop a 'Delay' icon after the 'Output' icon.

• Double click on it to open the configuration dialogue box, and then:

• Change the 'Display name:' to "For 10 seconds".
• Leave the 'Delay value:' as '1'.
• Change the unit to 'seconds.
• Click on 'OK'.

(Again, the resulting dialogue box is shown opposite.)

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Finally, we need to turn off the lamp, after the ten second delay.

To do this:

• Drag and drop a second 'Output' icon after the 'Delay' icon.
• Double click on it to allow you to configure it.

Rename it "Switch off", and configure it to deliver value "0" to single bit 0 of Port B.

The resulting dialogue box is shown opposite.

You should now save the flowchart as "Lamp1.fcf", and close Flowcode.

What next

The next step is to add the switch and lamp to the flowchart. This is covered in the exercise Adding Devices to a Flowchart.