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

Page 274 · What’s a Microcontroller?

Imagine that Pos. 126 is closed. If you want to set the tap to 125, (open pos. 126 and close pos. 125), set U/D low, then apply a pulse to CLK. If you want to set the tap to Pos 127, set U/D high, and apply 2 pulses. If you want to bring the tap down to 1, set U/D low, and apply 126 pulses.

This next example program uses the Debug Terminal to ask you which tap setting you want. Then it decides whether to set the U/D pin high or low, and applies the correct number of pulses to move the tap from its old setting to the new setting.

With the exception of EEPROM Data, the next example program also has all the sections you could normally expect to find in an application program:

•Title – comments that include the filename of a program, its description, and the Stamp and PBASIC directives.

•EEPROM Data – The DATA declarations used by the program.

•I/O Definitions – constant declarations that define I/O pin numbers.

•Constants – constant declarations that define other values used in the program.

•Variables – variable declarations.

•Initialization – a routine that gets the program started on the right foot. In this next program, the potentiometer’s tap needs to be brought down to zero.

•Main – the routine that handles the primary jobs the program has to do.

•Subroutines – the segments of code that do specific jobs, either for each other, or in this case, for the main routine.

Example Program: TerminalControlledDigtialPot.bs2

You can use this example program and the Debug Terminal to set the digital pot’s tap. By changing the tap setting on the digital pot, you change the brightness of the LED connected to the transistor that the digital pot controls. Figure 9-9 shows an example of entering the value 120 into the Debug Terminal’s Transmit Windowpane while the program is running. Since the old tap setting was 65, the LED becomes nearly twice as bright when it is adjusted to 120.

Chapter #9: Electronic Building Blocks · Page 275

√Enter and run TerminalControlledDigtialPot.bs2.

√Enter values between 0 and 127 into the Debug Terminal. Make sure to press the enter key after you type in the digits.

'-----[ Title ]-----------------------------------------------------------

'What's a Microcontroller - TerminalControlledDigitalPot.bs2

'Update digital pot's tap based on Debug Terminal user input.

'{$STAMP BS2}

'{$PBASIC 2.5}

'-----[ EEPROM Data ]-----------------------------------------------------

'-----[ I/O Definitions ]-------------------------------------------------

Chapter #9: Electronic Building Blocks · Page 277

FOR counter = oldTapSetting TO newTapSetting

PULSOUT ClkPin, 1

PAUSE DelayPulses

NEXT

Page 278 · What’s a Microcontroller?

SUMMARY

This chapter introduced integrated circuits and how they can be used with the BASIC Stamp. A transistor was used as a current valve, and a digital potentiometer was used to control the amount of current passing through the transistor. Examining the digital potentiometer introduced the reference notch and pin map as important elements of electronic chips. The function of each of the digital potentiometer pins was discussed, as well as the device’s internal structure. The PBASIC command TOGGLE was introduced as a means to save program memory.

Questions

1.What are the names of the terminals on the transistor you used in this chapter?

2.Which terminal controls the current passing through the transistor?

3.What can you do to increase or decrease the current passing through the transistor?

Exercise

1.Write a program that adjusts the tap in the digital pot to position 0 regardless of its current setting.

Project

1.Add a photoresistor to your project and cause the brightness of the LED to adjust with the brightness seen by the photoresistor.

Solutions

Q1. Emitter, base, and collector.

Q2. The base controls the current passing through the transistor.

Q3. Increase or decrease the current allowed into the transistor's base.

E1. To solve this exercise, look at TerminalControlledDigitalPot.bs2. The first thing it does, in the Initialization section, is to set the tap to the lowest position. This exact code is used in the solution below.

'What's a Microcontroller - Ch9Ex01_SetTapToZero.bs2

'Turn tap on digital pot all the way down to zero

'{$STAMP BS2}

'{$PBASIC 2.5}

DEBUG "Program Running!"

Read_Photoresistor:

HIGH PhotoPin

PAUSE 100

RCTIME PhotoPin, 1, lightReading

RETURN

Further Investigation

“Industrial Control”, Student Guide, Version 2.0, Parallax Inc., 2002

Industrial Control uses the transistor as an on/off switch for a resistor heating element. It also uses a phototransistor to detect the passage of stripes on a spinning wheel.

Chapter #10: Running the Whole Show · Page 281

Chapter #10: Running the Whole Show

SUBSYSTEM INTEGRATION

Most of the activities in this text introduce how to program the BASIC Stamp to interact with one or two circuits at a time. Many microcontrollers have to handle tens or even hundreds of circuits. This chapter will demonstrate a few of the techniques used to manage a variety of circuits with a single microcontroller. Programming the microcontroller to orchestrate the activities of different circuits performing unique functions is called subsystem integration.

The example in this chapter uses a sensor array consisting of two pushbutton circuits, a potentiometer circuit and a photoresistor circuit. The activities in this chapter will guide you through building and testing each subsystem individually. After each subsystem is built and tested, you will then write a program that combines each subsystem into a working unit. Figure 10-1 shows the circuit schematic for the system you will build, and the master parts list is below.

Always remember: whenever possible, test each subsystem individually before trying to make them work together. If you follow this rule, your projects will go much more smoothly, and your chances of success will be greatly improved. The activities in this chapter will guide you through the process.

Sensor Array Parts List

(4) Resistors – 220 Ω (red-red-brown)

(2) Resistors – 10 kΩ (brown-black-orange)

(2) Pushbuttons – normally open

(2) Capacitors – 0.1 µF

(1) Potentiometer – 10 kΩ

(1) Photoresistor

(5) Jumper wires