What is a Microcontroller (Paralax, v2.2, student guide, 2004)

Page 62 · What’s a Microcontroller?

Bi-Color LED Circuit Parts

(1) LED – bi-color

(1) Resistor 470 Ω (yellow-violet-brown)

(1) Jumper wire

Building and Testing the Bi-Color LED Circuit

Figure 2-18 shows the manual test for the bi-color LED.

√Disconnect power from your Board of Education or HomeWork Board.

√Build the circuit shown on the left side of Figure 2-18.

√Reconnect power and verify that the bi-color LED is emitting red light.

√Disconnect power again.

√Modify your circuit so that it matches the right side of Figure 2-18.

√Reconnect power.

√Verify that the bi-color LED is now emitting green light.

√Disconnect power.

Chapter #2: Lights On – Lights Off · Page 65

The bi-color LED will also turn off if you send high signals to both P14 and P15. Why? Because the electrical pressure is the same at P14 and P15 regardless of whether you set both I/O pins high or low.

Example Program: TestBiColorLED.bs2

√Reconnect power.

√Enter the TestBiColorLed.bs2 code into the BASIC Stamp Editor.

√Run the program.

√Verify that the LED cycles through the red, green, and off states.

'What's a Microcontroller - TestBiColorLed.bs2

'Turn bi-color LED red, then green, then off in a loop.

'{$STAMP BS2}

'{$PBASIC 2.5}

DEBUG "Program Running!"

Your Turn – Lights Display

In Activity #3, a variable named counter was used to control how many times the LED blinked. What happens if you use the value counter to control the PAUSE command’s Duration argument?

√Rename and save TestBiColorLed.bs2 as TestBiColorLedYourTurn.bs2.

√Add a counter variable declaration before the DO statement:

Page 66 · What’s a Microcontroller?

counter VAR BYTE

√Nest the FOR…NEXT loop below within the DO…LOOP.

FOR counter = 1 to 50

HIGH 15

LOW 14

PAUSE counter

LOW 15

HIGH 14

PAUSE counter

NEXT

When you are done, your code should look like this:

counter VAR BYTE

DO

FOR counter = 1 to 50

HIGH 15

LOW 14

PAUSE counter

LOW 15

HIGH 14

PAUSE counter

NEXT

LOOP

At the beginning of each pass through the FOR…NEXT loop, the PAUSE value (Duration argument) is only one millisecond. Each time through the FOR…NEXT loop, the pause gets longer by one millisecond at a time until it gets to 50 milliseconds. The DO…LOOP causes the FOR…NEXT loop to execute over and over again.

√Run the modified program and observe the effect.

Chapter #2: Lights On – Lights Off · Page 67

SUMMARY

The BASIC Stamp can be programmed to switch a circuit with a light emitting diode (LED) indicator light on and off. LED indicators are useful in a variety of places including many computer monitors, disk drives, and other devices. The LED was introduced along with a technique to identify its anode and cathode terminals. An LED circuit must have a resistor to limit the current passing through it. Resistors were introduced along with one of the more common coding schemes you can use to figure out a resistor’s value.

The BASIC Stamp switches an LED circuit on and off by internally connecting an I/O pin to either Vdd or Vss. The HIGH command can be used to make the BASIC Stamp internally connect one of its I/O pins to Vdd, and the LOW command can be used to internally connect an I/O pin to Vss. The PAUSE command is used to cause the BASIC Stamp to not execute commands for an amount of time. This was used to make LEDs stay on and/or off for certain amounts of time. This amount of time is determined by the number used in the PAUSE command’s Duration argument.

The DO…LOOP can be used to create an infinite loop. The commands between the DO and LOOP keywords will execute over and over again. Even though this is called an infinite loop, the program can still be re-started by disconnecting and reconnecting power or pressing and releasing the Reset button. A new program can also be downloaded to the BASIC Stamp, and this will erase the program with the infinite loop.

Current direction and voltage polarity were introduced using a bi-color LED. If voltage is applied across the LED circuit, current will pass through it in one direction, and it glows a particular color. If the voltage polarity is reversed, current travels through the circuit in the opposite direction and it glows a different color.

Questions

1.What is the name of this Greek letter: Ω, and what measurement does Ω refer to?

2.Which resistor would allow more current through the circuit, a 470 Ω resistor or a 1000 Ω resistor?

3.How do you connect two wires using a breadboard? Can you use a breadboard to connect four wires together?

Page 68 · What’s a Microcontroller?

4.What do you always have to do before modifying a circuit that you built on a breadboard?

5.How long would PAUSE 10000 last?

6.How would you cause the BASIC Stamp to do nothing for an entire minute?

7.What are the different types of variables?

8.Can a byte hold the value 500?

9.What will the command HIGH 7 do?

Exercises

1.Draw the schematic of an LED circuit like the one you worked with in Activity #2, but connect the circuit to P13 instead of P14. Explain how you would modify LedOnOff.bs2 on Page 48 so that it will make your LED circuit flash on and off four times per second.

2.Explain how to modify LedOnOffTenTimes.bs2 so that it makes the LED circuit flash on and off 5000 times before it stops. Hint: you will need to modify just two lines of code.

Project

1.Make a 10-second countdown using one yellow LED and one bi-color LED. Make the bi-color LED start out red for 3 seconds. After 3 seconds, change the bi-color LED to green. When the bi-color LED changes to green, flash the yellow LED on and off once every second for ten seconds. When the yellow LED is done flashing, the bi-color LED should switch back to red and stay that way.

Solutions

Q1. Omega refers to the ohm which measures how strongly something resists current flow.

Q2. A 470 Ω resistor: higher values resist more strongly than lower values, therefore lower values allow more current to flow.

Q3. To connect 2 wires, plug the 2 wires into the same row of 5 sockets. You can connect 4 wires by plugging all 4 wires into the same row of 5 sockets.

Q4. Disconnect the power.

Q5. 10 seconds.

Q6. PAUSE 60000

Q7. Bit, Nib, Byte, and Word

Further Investigation

The resources listed here are available for free download from the Parallax web site and are also included on the Parallax CD.

“BASIC Stamp Manual”, Users Manual, Version 2.0c, Parallax Inc., 2000

The BASIC Stamp Manual has more examples you can try and information that further explains the following commands: HIGH, LOW, PAUSE, the DEBUG ? formatter, and FOR…NEXT.

“Basic Analog and Digital”, Student Guide, Version 2.0, Parallax Inc., 2003

Basic Analog and Digital uses LEDs to describe counting in binary, describes analog conditions, and it introduces new ways to adjust an LED’s brightness.

“BASIC Stamp Editor Help File”, PBASIC 2.5 Version 2.0 Parallax Inc., 2003

The PBASIC 2.5 Help File has information on DO…LOOP, which is new to PBASIC 2.5 and not included in the BASIC Stamp Manual. You can find this information by clicking the book icon on your BASIC Stamp Editor task bar, then selecting PBASIC Reference from the menu in the left sidebar window. This will open the PBASIC Command Reference alphabetical listing in the main window. Detailed information can be found by clicking on each command.

Chapter #3: Digital Input - Pushbuttons · Page 71

Chapter #3: Digital Input - Pushbuttons

FOUND ON CALCULATORS, HAND HELD GAMES, AND APPLIANCES

How many devices with pushbuttons do you use on a daily basis? Here are a few examples that might appear in your list: computer, mouse, calculator, microwave oven, handheld remote, handheld games, and VCR. In each device, there is a microcontroller scanning the pushbuttons and waiting for the circuit to change. When the circuit changes, the microcontroller detects the change and takes action. By the end of this chapter, you will have experience with designing pushbutton circuits and programming the BASIC Stamp to monitor them and take action when changes occur.

RECEIVING VS. SENDING HIGH AND LOW SIGNALS

In Chapter #2, you programmed the BASIC Stamp to send high and low signals, and you used LED circuits to display these signals. Sending high and low signals means you used a BASIC Stamp I/O pin as an output. In this chapter, you will use a BASIC Stamp I/O pin as an input. As an input, an I/O pin listens for high/low signals instead of sending them. You will send these signals to the BASIC Stamp using a pushbutton circuit, and you will program the BASIC Stamp to recognize whether the pushbutton is pressed or not pressed.

Other terms that mean send, high/low, and receive: Sending high/low signals is described in different ways. You may see sending referred to as transmitting, controlling, or switching. Instead of high/low, you might see it referred to as binary, TTL, CMOS, or Boolean signals. Another term for receiving is sensing.

ACTIVITY #1: TESTING A PUSHBUTTON WITH AN LED CIRCUIT

If you can use a pushbutton to send a high or low signal to the BASIC Stamp, can you also control an LED with a pushbutton? The answer is yes, and you will use it to test a pushbutton in this activity.

Introducing the Pushbutton

Figure 3-1 shows the schematic symbol and the part drawing of a normally open pushbutton. Two of the pushbutton’s pins are connected to each terminal. This means that connecting a wire or part lead to pin 1 of the pushbutton is the same as connecting it to pin 4. The same rule applies with pins 2 and 3. The reason the pushbutton doesn’t just