main.cpp

00001 #include "mbed.h"
00002 
00003 // MCP4141. 2.7 to 5.5V 7-bit linear digital potentiometer with SPI interface.
00004 // Wiper commands can be write or read. This program is to write commands only.
00005 // MOSI/MISO are multiplexed in the MCP4141 side.
00006 
00007 // Author: Lluis Nadal. August 2011.
00008 
00009 
00010 DigitalOut leds[] = {(LED1), (LED2),(LED3),(LED4)};
00011 
00012 //Define SPI mBed side:
00013 SPI spi(p5, p6, p7); // mosi, miso, sclk. To write commands only, you do not need to connect p6(miso) to MCP4141.
00014 DigitalOut cs(p8); // Chip select. Active low.
00015 
00016 /*
00017 MCP4141 side:
00018 p8 = Vdd: +3.3V. p4 = Vss: GROUND. p1: cs (mBed's p8).
00019 p2: sclk (mBed's p7). p3: SDI (mBed's p5). p5: potentiometer a. p7: potentiometer b.
00020 Rab: 5k, 10k 50k or 100k options. p6: wiper (75 Ohm).
00021 Attach ohmeter to pins p6 and p7.
00022 */
00023 
00024 void write(int n) { // 0 >= n <= 128
00025     cs=1;
00026     cs=0;
00027     spi.write(0x00); // Address(volatile) 0000, write=00, data=00 = 0x00
00028     spi.write(n); // Data 
00029     cs=1;
00030 }
00031 
00032 void increment() {
00033     cs=1;
00034     cs=0;
00035     spi.write(0x07);// Address(volatile) 0000, increment 0100 = 0x07
00036     cs=1;
00037 }
00038 
00039 void decrement() {
00040     cs=0;
00041     spi.write(0x0B);// Address(volatile) 0000, decrement 1000 = 0x0B
00042     cs=1;
00043 }
00044 
00045 
00046 
00047 int main() {
00048 
00049     cs=1; // Disables MCP4141
00050 
00051     spi.format(8,0); // 8 bits , mode 0
00052     spi.frequency(1000000); // Default SPI frequency. ( 250kHz maximum for read commands).
00053 
00054     while (1) {
00055 
00056         leds[0]=0;
00057         leds[1]=0;
00058         leds[2]=0;
00059         leds[3]=0; // All leds off.
00060         wait(1);
00061         
00062         write(32);// Set wiper to 32/128 = 1/4 Rab
00063         leds[0]=1;
00064         wait(4);
00065 
00066         write(64);// Set wiper to 64/128 = 1/2 Rab
00067         leds[1]=1;
00068         wait(4);
00069 
00070         write(96);// Set wiper to 96/128 = 3/4 Rab
00071         leds[2]=1;
00072         wait(4);
00073 
00074         // Decrement wiper 10 times
00075         for (int i=0; i<10; i++) {
00076             decrement();
00077         }
00078         leds[3]=1;
00079         wait(4);
00080 
00081         // Increment wiper 10 times
00082         for (int i=0; i<10; i++) {
00083             increment();
00084         }
00085 
00086         leds[3]=0;
00087         wait(4);
00088 
00089     }
00090 
00091 }