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USB I/O Board (Microchip usb port drive)

I/O board USB connection

Hi-res board image

 

Board Description

You can power the board by USB bus.
The USB can supply 500mA, so there is enough power to drive relays and displays. The microcontroller has a USB port on board . You can drive up to 8 relays and read the status of 8 optocoupler. You can use this inputs for switches, push buttons, or to have a feed back to see if the relays have been effectively switched. The communication protocol between PC and board is very simple, for example, sending the character "6" on the virtual RS232 the first relay will turn on and the board will replay with an "I" character, this response is an acknowledge and makes you sure that the command arrived and was correctly executed.

 

scheda rele opto

 

HW description

The board is made of:

  • PCB;
  • microcontroller Microchip (18f2455 -see the Datasheet) with 32 Kb off flash memory, 256 byte of Eeprom memory and controller USB;
  • Optocoupler for input (TPL4N25-4).
  • USB Connector
  • Relays. We can mount two type of relay, one with maximum 30Vcc (or
    125Vac) or another with 230Vac, 2A contact.

Schematics

 

Schematic USB Board
Fig. 1

 

Schematic USB Board (2)
Fig. 2

 

Firmware description

The board firmware receives a command from the PC (using the get function) elaborate the command (by ProcessIO function) and executes the command(toggle the relay or read the input).
This is and example of the source code of the firmware:

void main(void)
{
/* A7  A6  A5  A4  A3  A2  A1  A0 */
/*    1     1     1     1    1     1     0     0 */
LATA &= 0x0; TRISA &= 0xFC; /* configure port A of uC */
/* B7 B6 B5 B4 B3 B2 B1 B0  */
/*    1   1    1    1   1    1   1    1  */
LATB &= 0x0; TRISB &= 0xFF; /* configure port B of uC */
/* C7 C6 C5 C4 C3 C2 C1 C0 */
/*   0    0    1    1   1    1   0    0 */
LATC &= 0x0; TRISC &= 0x3C; /* configure porta C of uC */
InitializeSystem();
mLED_1_Off(); 
MSB_num_restart = ReadEEPROM(0x20);
LSB_num_restart = RedEEPROM(0x21);
if ((MSB_num_restart == 0xFF)&(LSB_num_restart == 0xFF)){  
/* blank eeprom */
MSB_num_restart = 0 ;
LSB_num_restart = 0 ; 
WriteEEPROM ( 0x20, 0);
WriteEEPROM ( 0x21, 0);
}
else
{ 
if (LSB_num_restart == 0xFF){ 
MSB_num_restart = MSB_num_restart +1;
WriteEEPROM ( 0x20, MSB_num_restart);
WriteEEPROM ( 0x21, 0);
LSB_num_restart = 0;
}
else
{ 
LSB_num_restart = LSB_num_restart +1;
WriteEEPROM ( 0x21, LSB_num_restart);
}
}
EnablePullups();     /* enable pull-up on PORTB */
while(1)
{
USBTasks();        /*  USB Tasks  */
ProcessIO();        /* See user\user.c & .h */
}
}
void ProcessIO(void)
{   
if((usb_device_state < CONFIGURED_STATE)||(UCONbits.SUSPND==1)) return;
if(getsUSBUSART(input_buffer,1)){
...
if(input_buffer[0] == '6') /* 0x36 */ {
if(mUSBUSARTIsTxTrfReady()){
mRele_1_On();                /* turn on relay number 1*/
putrsUSBUSART("I");    /* acknoledge */
}
}
...
}
}

The ProcessIO() function waits for a command. On this example when the board receives the "6" character on virtual RS232 (the USB) the first relay will turn on and answer with "I" character. You can also read how many time the board has been turned on, this counter is saved on the eeprom memory inside the PIC microcontroller.

Software description

Here is an example of software written with Visual Basic. From left ToolBox import the "SerialPort" control. We will use 3 functions of this control, which are: Open, Write, Read


Let's start opening the serial port, with SerialPort.Open.


The SerialPort.Open needs a serial port number to be opened; it is the number
of the virtual serial port (usually it is COM4).
After the virtual serial port is opened, you can send commands using
SerialPort.Write function, for example if you want to turn on the first relay:
SerialPort.Write("6")

To read the answer from the board and to acknowledge the command received
use the SerialPort.Read function

 

scheda rele visual basic

 

Command protocol

Send 0 = 0x30 = 48 => Turn on Led and answer  "A"
Send 2 = 0x32 = 50 => Turn off Led and answer  "C"
Send 5 = 0x35 = 53 => if the puss button is pressed, answer  "G" 
otherwise "H"
Send 6 = 0x36 = 54 => Turn on Relay 1 and answer  "I"
Send 7 = 0x37 = 55 => Turn off Relay 1 and answer  "L"
Send 8 = 0x38 = 56 => Turn on Relay 2 and answer  "M"
Send 9 = 0x39 = 57 => Turn off Relay 2 and answer  "N"
Send a = 0x61 = 97 => Turn on Relay 3 and answer  "O"
Send b = 0x62 = 98 => Turn off Relay 3 and answer  "P"
Send c = 0x63 = 99 => Turn on Relay 4 and answer  "Q"
Send d = 0x64 = 100 => Turn off Relay 4 and answer  "R"
Send e = 0x65 = 101 => if input 1 is on, answer  "S" otherwise "T"
Send f = 0x66 = 102 => if input 2 is on, answer  "U" otherwise "V"
Send g = 0x67 = 103 => if input 3 is on, answer  "W" otherwise "Y"
Send h = 0x68 = 104 => if input 4 is on, answer  "J" otherwise "K"
Send i = 0x69 = 105 => if input 5 is on, answer  "Z" otherwise "a"
Send l = 0x6C = 108 => if input 6 is on, answer  "b" otherwise "c"
Send m = 0x6D = 109 => if input 7 is on, answer  "d" otherwise "e"
Send n = 0x6E = 110 => if input 8 is on, answer  "f" otherwise "g"
Send o = 0x6F = 111 => Turn on Relay 5 and answer  "H"
Send p = 0x70 = 112 => Turn off Relay 5 and answer  "B"
Send q = 0x71 = 113 => Turn on Relay 6 and answer  "D"
Send r = 0x72 = 114 => Turn off Relay 6 and answer  "E"
Send s = 0x73 = 115 => Turn on Relay 7 and answer  "F"
Send t = 0x74 = 116 => Turn off Relay 7 and answer  "G"
Send u = 0x75 = 117 => Turn on Relay 8 and answer  "X"
Send v = 0x76 = 118 => Turn off Relay 8 and answer  "m"

You can also read how many time the board has been powered up:

Send w = 0x77 = 119 => Read the Most significant part of number of restart
Send z = 0x7A = 122 => Read the Least significant part of number of restart

 

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AttachmentSize
SW_PC_Relay_USB.zip289.38 KB

"USB can supply 500mA" Are

"USB can supply 500mA" Are You sure?

USB Port Power Capabilities.

It seems that an USB HOST Port should at least be capable to source 100mA (a unit load, am I wrong?). Usually a PC USB Host should be capable to handle up to 5 unit loads, hence 500mA.
Perhaps if you want to use this USB i/o board, make sure your PC USB port can provide the required amount of power to the board.

USB power supply it's a big problem....

USB power supply it's a big problem....
The usb specification are clear: Initial Power supply must be 100mA then, after negotiation and device request, the host can supply to 500mA.
But many mother boards connect the usb_vcc directly to the main power supply (only a fuse in the middle), so how can the fuse respond to usb device additional power request?

Conclusion: keep you 500mA and don't care about usb specification (with its consequences)

USB Board, Serial Protocol

This protocol to interface an USB board seems to be designed for a simple VB module....

Take a look at Arduino, i'm

Take a look at Arduino, i'm enthusiast of it

Sure, i know Arduino boards,

Sure, i know Arduino boards, they are great, but there are 2 big differences:

1) Arduino embedds an Atmel Microcontroller
(The usb i/o board uses Microchip Picmicro)

2) USB I/O Board can drive up 4 onboard relays, so you can easily and quickly have a "usb to relays" solution

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