How to Use PICAXE-28: Examples, Pinouts, and Specs

The PICAXE-28 is a microcontroller development board featuring a 28-pin PICAXE chip. It is designed for ease of programming and prototyping, making it an excellent choice for beginners and hobbyists. The PICAXE-28 is widely used in educational environments and DIY projects to control electronic devices, sensors, and actuators. Its simplicity and versatility make it a popular tool for learning programming and electronics.

• Robotics and automation projects
• Sensor data acquisition and processing
• Motor control systems
• Educational programming exercises
• Home automation and IoT prototypes

The PICAXE-28 microcontroller board is built around a PICAXE chip, which is preloaded with a BASIC interpreter for easy programming. Below are the key technical details:

• Operating Voltage: 4.5V to 5.5V
• Clock Speed: 4 MHz (internal resonator)
• I/O Pins: 22 (16 digital, 6 analog)
• Programming Language: PICAXE BASIC
• Memory:
  • 256 bytes of EEPROM
  • 2048 bytes of program memory
• Communication Protocols: Serial (via programming cable)
• Power Supply Options: Battery or regulated DC supply
• Current Consumption: ~2 mA (active), ~50 µA (sleep mode)

The PICAXE-28 has a 28-pin layout. Below is the pin configuration:

1. Powering the Board:

   • Connect a 4.5V–5.5V DC power supply to the V+ and GND pins.
   • Alternatively, use a 3xAA battery pack for portable applications.

2. Programming the PICAXE-28:

   • Install the PICAXE Programming Editor software on your computer.
   • Connect the PICAXE-28 to your computer using a PICAXE USB programming cable.
   • Write your program in PICAXE BASIC and upload it to the microcontroller.

3. Connecting Peripherals:

   • Use the I/O pins to connect LEDs, sensors, motors, or other devices.
   • For analog sensors, connect them to the ADC pins (ADC 0–3).

4. Running the Program:

   • Once the program is uploaded, the PICAXE-28 will execute it automatically.
   • Use the serial output pin to monitor data or debug your program.

• Always ensure the power supply voltage is within the specified range to avoid damaging the microcontroller.
• Use pull-up or pull-down resistors for unused input pins to prevent floating states.
• Avoid drawing excessive current from the I/O pins (maximum 20 mA per pin).

Below is an example of a simple program to blink an LED connected to I/O pin 0:

' Blink an LED connected to I/O pin 0
' Ensure the LED has a current-limiting resistor (e.g., 330 ohms)

main: 
    high 0          ' Turn on the LED
    pause 1000      ' Wait for 1 second
    low 0           ' Turn off the LED
    pause 1000      ' Wait for 1 second
    goto main       ' Repeat the loop

To read an analog sensor connected to ADC 0, use the following code:

' Read an analog sensor connected to ADC 0 and display the value via serial

symbol sensorValue = b0  ' Define a variable to store the sensor value

main:
    readadc 0, sensorValue  ' Read the analog value from ADC 0
    sertxd ("Sensor Value: ", #sensorValue, 13, 10)  ' Send value via serial
    pause 500              ' Wait for 500 ms
    goto main              ' Repeat the loop

1. The PICAXE-28 is not responding to programming commands:

   • Ensure the programming cable is securely connected to both the computer and the PICAXE-28.
   • Verify that the correct COM port is selected in the programming software.
   • Check the power supply to ensure the board is powered on.

2. The program is not running after upload:

   • Confirm that the program was successfully uploaded without errors.
   • Ensure the correct pins are used for connecting peripherals.

3. Analog readings are inconsistent:

   • Use a decoupling capacitor (e.g., 0.1 µF) between the ADC pin and GND to reduce noise.
   • Verify that the sensor is properly connected and powered.

4. The microcontroller overheats:

   • Check for short circuits or excessive current draw from the I/O pins.
   • Ensure the power supply voltage does not exceed 5.5V.

Q: Can I use the PICAXE-28 with an external clock?
A: Yes, the PICAXE-28 supports external clock sources, but the default internal 4 MHz resonator is sufficient for most applications.

Q: What is the maximum current output of the I/O pins?
A: Each I/O pin can source or sink up to 20 mA, with a total maximum current of 90 mA for all pins combined.

Q: Can I use the PICAXE-28 for wireless communication?
A: Yes, you can interface the PICAXE-28 with wireless modules like Bluetooth or RF transceivers using the serial communication pins.

Q: Is the PICAXE-28 compatible with Arduino shields?
A: No, the PICAXE-28 is not directly compatible with Arduino shields due to differences in pin layout and functionality.

By following this documentation, you can effectively use the PICAXE-28 for a wide range of projects and applications.