Easy Programming STM32F407 Discovery Board with mbed

Why?

STM32F407 Discovery board does not directly support MBED online IDE. But the mcu on this board is also used in another official MBED board ( Seeed Studio Arch Max v1.1 ) . So, it is possible to program Discovery board by treating it as an Arch Max board.

• It's an easy way for rapid prototyping with online IDE of MBED. No need to install Keil/IAR/AC6 on PC and go through painful setup.
• Common things like ADC/PWM/DAC/GPIO/UART/SPI/I2C can be used with minimum configuration.
• On board accelerometer is also tested.

Attached code below demonstrates all these functionalities.

Step 1: Go to mbed.org and login/signup

Step 2: Select Platform Seeed Arch Max

Step 3: Edit, Compile and Download Code

Following code demonstrated GPIO, ADC, Serial, PWM and On board Accelerometer capabilities

Library:

#include "mbed.h"
#include "LIS3DSH.h"

GPIO and Pwm Initialization:

DigitalOut rLED(PD_14);   // on board red LED, DO
DigitalOut bLED(PD_15);   // on board blue LED. DO
DigitalOut gLED(PD_12);   // on board green LED, DO
DigitalOut oLED(PD_13);   // on board orange LED, DO
PwmOut GLED(PA_9);        // on board green LED, 
PWMDigitalIn  pbSW(PA_0);    // on board blue PUSH Switch, active high DI 

Serial and ADC:

Serial serial(PA_2,PA_3); // serial com tx, rx UART
AnalogIn   adcPB0(PB_0);  // PB0 as 12 bit ADC

Serial baud and print:

  // set serial baud and print welcome msg //    
serial.baud(19200);    
serial.printf("Welcome to STM32F407 Development with mbedOS nr"); 

PWM Frequency and Duty Cycle:

GLED.period(1.0f/freq);  // set pwm period
GLED.write(duty/100.0f); // set pwm duty cycle 

LED Blink:

 rLED = 1;
 gLED = 1;
 wait(delay);
 rLED = 0;  
 gLED = 0;   
 wait(delay);

ADC Read:

  // adc value read // 
  adcval = 4095*adcPB0.read_u16()/65535; // 12 bit value                    

Pins shared with on board hardware

Update 1: DAC works on PA4 and PA5

Just tested 12 bit DAC on A4 and A5 pins. It works. But, Accelerometer and Audio might not be used along with DAC for other application (same pin).

DAC Setup:

// Before main
AnalogOut dac1(PA_5); 
AnalogOut dac2(PA_4);

Output Analog Voltage:

// set up 1 volt on dac 1
dac1 = 0.333f; // vdd* 0.333 = 3.0*0.333 =  1.0 volt
// set up 1.5 volt on dac 2
dac2 = 0.5f; // vdd*0.5 = 1.5 volt

Update 2: 20x4 LCD support

Tested lcd display with mbed, working great ! 5 volts display runs with 3.3 v logic without issues. Code link will be added after final testing.

Caveats

Not all functions will work according to above pin map. For example Pwm on PD13 will not work on mbed. Because, mbed compiler treats the code according to Arch Max boards pin mapping.

For, pin specific function that will work for sure, see the pin map attached below.

External Resources

Farrukh's Tutorial

Arch Max Pin Map

STM32F407 Technical Docs

mbed DigitalOut

mbed DigitalIn

mbed PwmOut

mbed Serial

mbed AnalogIn