Raspberry Pi with Relay I/O Board




Relay I/O Board is widely used in applications of smart home project. In this article, I will detail how to control the Relay I/O board using Raspberry Pi with Raspberry Pi Universal Expansion Board via internet. The codes and schematic diagrams used in this article was listed at the end of this article.

Part I: Hardware

1. Pin Mapping

The CPLD on the Raspberry Pi Universal Expansion Board can be used to map pins between modules. For this project, we want to map pins as following diagram Fig.1.

Raspberry Pi with Relay I O BoardThis part is pretty easy since we only need to map the UART1 of the STM32 to the Raspberry Pi and PC10, PC11 of the STM32 to the Relay I/O board using the CPLD. The following Verilog code can implement the idea:

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module RS232(RXD_in,TXD_in,RXD_out,TXD_out,
K1_in,K1_out,K2_in,K2_out);
input   RXD_in, TXD_in,K1_in,K2_in;
output  RXD_out,TXD_out,K1_out,K2_out;
assign RXD_out = RXD_in;
assign TXD_out = TXD_in;
//assign pins for relays K1 and K2
assign K1_out = K1_in;
assign K2_out = K2_in;
endmodul

We can flash the design into the CPLD right now.

2. STM32 Configuration

Creating a new .c source code file RelayIOBoard.c as the driver of the Relay I/O board:

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/*Driver for Relay IO board*/
#include < stm32f10x.h>
#include < stdio.h>
#define on  1
#define off 0
int k1_state;
int k2_state;
void Relay(int relay_num, int on_off){
  switch( relay_num )
  {
    case 1:
            //For K1 which is controlled by the PC10
        if(on_off == on)
                {
         GPIO_SetBits(GPIOC, GPIO_Pin_10);
                 k1_state = on;
        }
        if(on_off == off)
                {
         GPIO_ResetBits(GPIOC, GPIO_Pin_10);
                 k1_state = off;
        }              
        break;
    case 2 :
            //For K2 which is controlled by the PC11
        if(on_off == on)
                {
         GPIO_SetBits(GPIOC, GPIO_Pin_11);
                 k2_state = on;
        }
        if(on_off == off)
                {
         GPIO_ResetBits(GPIOC, GPIO_Pin_11);
                 k2_state = off;
        }      
        break;
  }
}
void Get_Relay_States(void){
   if(k1_state == on){
      printf("k1on\r\n");
   }
     else{
      printf("k1off\r\n");
   }
   if(k2_state == on){
      printf("k2on\r\n");
   }
     else{
      printf("k2off\r\n");
   }
}
void Relay_init(void )
{
  Relay(1,off);
    Relay(2,off);
    k1_state =off;
    k2_state =off;
}

Raspberry Pi with Relay I O Board Schematic

We need to add following commands to the Shell() in CommandShell.c:

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//Command K1 on
if(IsStringMatch(Command,"k1on",Counter)){
     Relay(1, 1);
    printf("k1on\r\n");
  }
//Command K1 off
if(IsStringMatch(Command,"k1off",Counter)){
     Relay(1, 0);
    printf("k1off\r\n");
  }
//Command K2 on
if(IsStringMatch(Command,"k2on",Counter)){
     Relay(2, 1);
    printf("k2on\r\n");
  }
//Command K2 off
if(IsStringMatch(Command,"k2off",Counter)){
     Relay(2, 0);
    printf("k2off\r\n");
  }
//Command krs, get relay states
if(IsStringMatch(Command,"krs",Counter)){
     Get_Relay_States();
  }

For convenience, the Firmware STM32_Relay_1.0.hex needs to be flashed into the MCU. The Firmware will host a Command Shell on UART1. It also includes the driver of the Relay I/O board.

3. Testing

Connecting Relay I/O Board to the Pmod1 socket on the Raspberry Pi Universal Expansion Board. A cooling fan may be controlled by the relay as following figure.

 

For more detail: Raspberry Pi with Relay I/O Board


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