Intellecta Technologies Pty Ltd

for PICAXE education, Roland CAM, Techsoft CAD, Intellecta control, Atmel, Arm and Microchip education

Introduction

The Control 7 is designed to control lights, motors, switches, and sensors. The actual program or set of instructions is downloaded into the microcontroller. This program then decides if the motors come on when the switches are pressed or other actions.

This section discusses:

• · Connections
• · Connecting leds, lamps and solenoid drivers
• · Connecting motors
• · Connecting switches
• · Connecting sensors
• · Setting up operation from 24V

Device Connections

The adjoining  diagram shows the various connections to the PICAXE18 or Atmel controller.

The connections are simple apart from the need for the reset switch that resets the microcontroller when the push button is pressed.

Device Connections and links to PICAXE lines

The programming statements in the PICAXE device are based on making appropriate pins HIGH or LOW.

For example, to turn on the Light 1 requires a HIGH 4 statement.

The figure shows the relationship between the various devices and the connections on the PICAXE device. when the push button is pressed.

It is useful to consider the pins statement that sets up the high or low on 8 lines immediately.

For example:

let pins = %11111111 turns on all the lines.

let pins = %00000010 turns on line 1 only

Main schematic for PICAXE and Serial connections

The above figure shows the circuit for the microcontroller and the outside serial port connector and the reset push button.

Pressing the reset pushbutton stops the operation of the device and sets it to the start of the program.

The labels such as IN1 and IN2 etc are called NET LABELS and these name the connections on both the device U1 and other devices on the board. For example, you will see that pin 6 has a label OUT0 and this also is connected to the motor controller device.

You will also see that the device labels such as C5, C6, R5 etc correspond to components on the circuit board

Switches

The PICAXE trainer accepts two switch inputs from external switches. The two wires from each connection are connected to a push button switch or similar that directly links the 5V power supply through a LED to the ground connection.

The LED will illuminate when the switch is pressed and the voltage at the IN7 and IN6 line will ris eto 5V or an ON value.

Note that the switches must be mechanical switches that directly short the contacts. The keyboard membrane switches have a resistance value and will not operate in this simple system.

The state o fthe switches can be read with the following BASIC instructions.

If PIN7 = 1 then Flash ‘ If the switch is pressed then goto the label FLASH

Sensor inputs

The PICAXE accepts two sensor inputs that can vary between 0 and 5V range.

Three terminals are located for the sensors which correspond to 0V, signal value and 5V.

The channels correspond to IN1 and IN2

To read the sensor value you can use the following BASIC instructions.

readadc 1, b0 “ read from 1 into variable b0.

Connection of sensors

The following figure shows how to connect up sensors such as thermistors and light dependent resistors.

The value of the resistor is determined by the choice of sensor and its resistance at room temperature of ambient light intensity.

For example, measure the resistance of the light dependent resistor under normal illumination. If the value is 100K then choose this value. The voltage at the middle input pin will be 2.5V because the simple circuit is a potential divider.

Light Outputs

Two lights, LEDS, single direction motors or solenoid valves can operate from the two light connections.

Nornally, the EXTERNAL Voltage is set to 5V with the jumper LK1 located near the power supply connector.

This means that the transistors inside the driver chip have 5 volts through the device and this is switched to ground.

Current then flows through the device.

For example, to connect an LED to the Light connector follow the next figure.

A current limiting resistor must be used to prevent damage to the LED.

If you want to connect a 24V solenoid for pneumatics applications then wire the solenoid between these two connections.

Check if there is any polarity requirement on the particular brand of solenoid valve.

Motor control

Two small bidirectinal DC motors can be controlled with the Control 7 trainer.

A special H Bridge motor driver chip is used to control the motor and the motion depends on the state of the two input lines to each motor. The adjoining figure shows the value of the input lines in1, in2 on the device and the direction of rotation.

The 293D component has high current capacity and will not be damaged by excessive currents because it will turnoff.

Be careful using cheap and noisy motors that may upset the PICAXE controller. ( stay away from motors that produce small sparks and noise).

For example:

Motor 1 is controlled with OUT0 and OUT1 lines from the PICAXE.

To turn the motor forward use the following code

: MatorForward ‘ define a subroutine

High 0

Low 1

Return

Similarly, reverse the High 0, Low 1 to Low 0, High 1 to reverse the motor direction.

Go to the first program