This article is the second part of 'Wireless power transfer system for rehabilitation' and details the development of the first prototype of the system, built to test the components and gain an idea of the wireless power transfer system.

Development Log

Part 1: Motor Driver and MCU Testing

As mentioned previously, the transmitting side will be built as the basic structure first.

Choosing the ‘right’ components is a key part of the project. At this point, the reason for choosing STM32F407VG Discovery as the MCU is that STM32F407VG is a general-use and easy-to-use MCU. The Discovery Board is easier to handle than a chip STM32 MCU. A motor driver DRV8412 is used since it is also an easy-to-use component. DRV8412 includes 2 full-bridge (or 4 half-bridge) inside the IC. Once the MCU sends serval PWM signals to the driver, the driver can output AC power to drive the coils. And also, there are error protections built in the IC, including Under-voltage protection, Overcurrent Protection, Overtemperature Protection and Device Protection System. Those features of the DRV8412 driver make the IC easy to implement and friendly for beginners.

The system is built similarly with the application example from the datasheet of DRV8412. To make the system more flexible and universal, the M1, M2, and M3 (mode selection pins) are connected to the MCU.

In our application, Dual full bridges are designed. Then the mode selection pins should be 000.

In the above diagram, the value of the R_{oc_adj} will determine the Overcurrent (OC) threshold. In the project, 150kΩ R_{oc_adj} is used.

This is the schematic diagram of the system. The PCB Layout will be like the image shown below.

This is the PCB layout for the system. After adding the ground plane and vias, the layout is ready to print out. Please make sure that the wires of outputs are wide enough. “Pour copper shape” is used in the design to draw the wider wire for the outputs.

This is the product of the system. And it is ready for use.

Components list

Software

Then, it is time for the software part.

To program the STM32F407 Discovery Board, Keil is used as the tool. Keil can be downloaded from http://www.keil.com/.

Step 1: Go to http://www.keil.com/

Step 2: Click “Download” on the header bar

Step 3: Click on “Product Downloads”

Step 4: Select “MDK-Arm”

Step 5: Type in the information and “Submit”

Step 6: Download and install the MDK-Arm software

Step 7: Open Keil and the pack installer

Step 8: Download “Keil::STM32F4xx-DFP”, “ARM::CMSIS”, “Keil::ARM_Compiler”, “Keil::MDK-Middleware”;

                (Version 1.0.8 Keil::STM32F4xx-DFP, version 5.0.1 ARM::CMSIS, version 1.3.0 Keil::ARM_compiler, version 7.4.0 Keil::MDK-Middleware are used in this project.)

(Some examples can be downloaded in pack installer which also help to learn the Discovery Board.)

Step 9: Open a project, Select “STMicroelectronics” -> “STM32F4 Series” -> “STM32F407” -> “STM32F407VG”

Then Keil is ready to use.

The program

#include "stm32f4_discovery.h"
#include <stdio.h>
#include <stm32f4xx_usart.h>
#include "stm32f4xx.h"
#include "stm32f4xx_tim.h"

/* ------------------------- Private typedef --------------------------------*/
GPIO_InitTypeDef  GPIO_InitStructure;
USART_InitTypeDef USART_InitStructure;
SPI_InitTypeDef  SPI_InitStructure;
TIM_OCInitTypeDef  TIM_OCInitStructure;
TIM_BDTRInitTypeDef TIM_BDTRInitStructure;
TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;

/*-------------------------- Initial Timer 1 and Timer 2 --------------------*/
void init_timer1_timer2(){
	RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM1,ENABLE);
	RCC_APB2PeriphClockCmd(RCC_APB1Periph_TIM2,ENABLE);
	//The clocks of different timers are different. 
	//Timer 1, 8 9-11 are using APB2, Timer 2-5, 12-14 are using APB1.
	//The frequency of APB2 is 168MHz, and frequency of APB1 is 84MHz. 
	//To calculate the value of TIM_Period:  
	//			PWM_frequency = clock of timer(84MHz or 168MHz) / (TIM_Period +1) 
	//			TIM_Period = clock of timer / PWM_frequency - 1
	//e.g.  to set the PWM frequency as 150kHz 
	//			TIM_Period for timer 1 = 168MHz / 150kHz - 1 = 1119
	//			TIM_Period for timer 2 = 84MHz / 150kHz - 1 = 559
	
	TIM_TimeBaseStructure.TIM_Period = 1119 ;
  TIM_TimeBaseStructure.TIM_Prescaler = 0;    
  TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
	TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;
	
  TIM_TimeBaseInit(TIM1, &TIM_TimeBaseStructure);
	
	TIM_TimeBaseStructure.TIM_Period = 559;
	TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);
	
	TIM_CtrlPWMOutputs(TIM1, ENABLE);
	TIM_CtrlPWMOutputs(TIM2, ENABLE);
}

/*-------------------------- Generater 4 PWM signals ------------------------*/
void init_PWM_ABCD(){
	TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2;
	TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
	TIM_OCInitStructure.TIM_OutputNState = TIM_OutputNState_Enable;
	TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low;
	TIM_OCInitStructure.TIM_OCNPolarity = TIM_OCNPolarity_High;
	TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Set;
	TIM_OCInitStructure.TIM_OCNIdleState = TIM_OCNIdleState_Reset;
	
	//To defind the duty cycle of each channel of each timer.
	//Channel 1 & 2 of Timer 1 & 2 are used in the system.
	//TIM_Pulse = (TIM_Period + 1) * %duty cycle - 1; 
	//e.g.	to set the PWM with 25% duty cycle
	//			TIM_Pulse for timer 1 = (1119+1) * 0.25 - 1 = 279
	//			TIM_Pulse for timer 2 = (559+1) * 0.25 - 1 = 139
	
	TIM_OCInitStructure.TIM_Pulse = 279;
	TIM_OC1Init(TIM1, &TIM_OCInitStructure);
	TIM_OC1PreloadConfig(TIM1, TIM_OCPreload_Enable);
	
	TIM_OCInitStructure.TIM_Pulse = 279;
	TIM_OC2Init(TIM1, &TIM_OCInitStructure);
	TIM_OC2PreloadConfig(TIM1, TIM_OCPreload_Enable);

	TIM_OCInitStructure.TIM_Pulse = 139;
	TIM_OC1Init(TIM2, &TIM_OCInitStructure);
	TIM_OC1PreloadConfig(TIM2, TIM_OCPreload_Enable);

	TIM_OCInitStructure.TIM_Pulse = 139;
	TIM_OC2Init(TIM2, &TIM_OCInitStructure);
	TIM_OC2PreloadConfig(TIM2, TIM_OCPreload_Enable);
}

/*-------------------------- Initial output PWM pins  -----------------------*/
void init_PWM_ABCD_pins(){
	RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOB, ENABLE);
	RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOE, ENABLE);
	
	GPIO_PinAFConfig(GPIOB, GPIO_PinSource10, GPIO_AF_TIM2);
	GPIO_PinAFConfig(GPIOB, GPIO_PinSource11, GPIO_AF_TIM2);
	GPIO_PinAFConfig(GPIOE, GPIO_PinSource9, GPIO_AF_TIM1);
	GPIO_PinAFConfig(GPIOE, GPIO_PinSource11, GPIO_AF_TIM1);
	
	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10|GPIO_Pin_11;
	GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
	GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
	GPIO_Init(GPIOB, &GPIO_InitStructure);

	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9|GPIO_Pin_11;
	GPIO_Init(GPIOE, &GPIO_InitStructure);	

	GPIO_ResetBits(GPIOB, GPIO_Pin_10|GPIO_Pin_11);
	GPIO_SetBits(GPIOB, GPIO_Pin_10|GPIO_Pin_11);

	GPIO_ResetBits(GPIOE, GPIO_Pin_9|GPIO_Pin_11);
	GPIO_SetBits(GPIOE, GPIO_Pin_9|GPIO_Pin_11);
}

/*-------------------------- Initial GPIO pins  -----------------------------*/
void init_GPIO(){	
	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_2|GPIO_Pin_4|GPIO_Pin_6; // M1, M2, M3 mode selection pins
	GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
	GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_2MHz;
	GPIO_Init(GPIOE, &GPIO_InitStructure);

	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10|GPIO_Pin_12;					// FAULT & OTW pins
	GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;							
	GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;										// Pull-up since the pins are active-low
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN;
	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
	GPIO_Init(GPIOE, &GPIO_InitStructure);

	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_13|GPIO_Pin_14;					// RESET_AB & RESET_CD pins
	GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
	GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;										// Pull-up since the pins are active-low
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
	GPIO_Init(GPIOE, &GPIO_InitStructure);
	
	//These are the setup pins for the Motor Driver DRV8412
	//M1, M2, M3 and RESET_AB RESET_CD are necessary
}



/*-------------------------- Main.c  -----------------------------*/
int main(void){
	SystemInit();
	init_LEDs();
	init_timer4();
	init_pwm_test();

	init_PWM_ABCD_pins();
	init_timer1_timer2();
	init_PWM_ABCD();
	
	init_GPIO();	
	GPIOE->BSRRH = GPIO_Pin_2|GPIO_Pin_4|GPIO_Pin_6;
	GPIOE->BSRRL = GPIO_Pin_13|GPIO_Pin_14;

  TIM_Cmd(TIM1, ENABLE);
	while (TIM1->CNT<=530){}
	TIM_Cmd(TIM2, ENABLE);
	while (1){}
}

After the program, the STM32F407 Discovery Board is ready to test and use.

First, check Out_A and Out_B pins (or Out_C and Out_D). Plug a 100ohm resistor into the terminal block for the coil, the current through the resistor is 100mA and the power consumption of the resistor is 1W. Please confirm that the current is not larger than 2A (current limit 2A is set in the system) and resistor power rating is correct. The result should be like the photo shown above. The signals have ~25% duty cycle and 150kHz.

The photo shows the voltage across the resistor.