4-20mA using SPI Interface

[gavo]

Hi All,

I came across a 4-20mA board from MicroElektronika which uses the SPI to control the device, has anyone used such a board before?, I am looking for Code Examples, would anyone be able to assist?

Regards,

gavo

[HenrikOlsson]

Is it too much to ask to at least post a link to the board in question?
I could try to find it on their site but I won't so the best answer *I* can give you is that you can use SHIFTOUT to do bitbanged SPI or use the MSSP module (if the PIC has one) to do it "in hardware".

/Henrik.

[alec]

Hi

This is some code I wrote to use that board as a basic loop calibrator. Worked OK for me.

Take care

Alec

'****************************************************************
'*  Name    : Encoder test                                      *
'*  Author  : alec noble                                        *
'*  Notice  : Copyright (c) 2012 alec noble                     *
'*          : All Rights Reserved                               *
'*  Date    : 9/27/2012                                         *
'*  Version : 1.0                                               *
'*  Notes   :                                                   *
'*          :                                                   *
'****************************************************************
#CONFIG
    __config _INTRC_OSC_NOCLKOUT & _WDT_ON & _MCLRE_ON & _LVP_OFF & _CP_OFF
#ENDCONFIG

'DEFINE OSC 20

'************************** setup LCD ****************************

	DEFINE	LCD_DREG	PORTB		' Set Data to PortB
	DEFINE 	LCD_DBIT	0			' Set starting Data to Bit4
	DEFINE 	LCD_RSREG   PORTB		' Set Register Select to PortB
	DEFINE 	LCD_RSBIT   4			' Set RS line to PORTB.4
	DEFINE 	LCD_EREG	PORTB		' Set Enable to PortB
	DEFINE 	LCD_EBIT  	5			' Set Enable line to PortB.5
	DEFINE 	LCD_BITS	4			' Set for 4 bit Bus
	DEFINE 	LCD_LINES	2			' Set number of lines to 

'*********************************************************************
CMCON = 7           'comparaters off - digital I/O on port A

trisb = 0           'all bits outputs
trisa = %00000111   'porta.0, 1, 2 input, all others output




cntr    var word
cntr_1  var word
cntr_2  var word
preset  var byte

sck var porta.6
sdi var porta.7
cs  var porta.4


cntr = 200
preset = 0
cs = 1

lcdout $FE, $01
pause 5
lcdout  "ahn_loop_cal"

pause 5000

lcdout $FE, $01
pause 5
lcdout dec cntr

'************************  Program **********************************

main:
    if porta.2 = 1 then set
    if porta.0 = 1 then CW
    if porta.1 = 1 then CCW
    goto main
    
    set:
    pause 5
    if porta.2 = 0 then main
    preset = preset + 1
    while porta.2 = 1 : wend
    if preset  > 4 then preset = 0
    lookup2 preset, [200, 400, 600, 800, 1000], cntr
    goto display
    
    CW:
    pause 5
    if porta.0 = 0 then main
    if cntr = 1023 then main
    cntr = cntr + 1
    goto display
    
    
    CCW:
    pause 5
    if porta.1 = 0 then main
    if cntr < 190 then main
    cntr = cntr - 1
    goto display
    
    display:
    cntr_1 = cntr * 4
    lcdout $FE, $01, dec cntr_1, " mV"
    pause 5
    cntr_2 = cntr_1/2
    lcdout $FE, $C0, dec2 cntr_2/100, ".", dec2 cntr_2//100, " mA"
    goto DAC_out
    
DAC_out:

    
    cntr_1.15 = 0
    cntr_1.14 = 0
    cntr_1.13 = 1       'GAIN OF 1
    cntr_1.12 = 1       'turn on DAC output
    low CS
'    pause 5
    shiftout sdi, sck, 1, [cntr_1\16]
    high cs
        
    while porta.0 or porta.1 = 1
    wend
    
    goto main

[gavo]

Hi Alec,

Many Thanks!, will try it!,

Hendrik the link is http://www.mikroe.com/click/rs485-5v/

Regards,

Gavin