/* This is my code for interacting with an external ADC DEVICE INFO: in my case it is a MCP3208, which recives 5 bits and send 12 bits SENDING: it has 2 bits for mode selection and the other 3 for selectng the right analog sensor RECIVE: first it send 2 null bites which I just ignore and then it send 12 bits which is the analog sensor reading MORE INFO: for the communication we use the built in registers for SPI communication, the SPI protocoll is very simple there is the chip select pin which identifies the chip we want to communicate to and there is the clock which gives the chip info when we are sending the next bit and finally there are the mosi and miso pins which are for incoming and outgoing data MANUAL: the chip manual can be found http://www.ereshop.com/shop/free/MCP3208.pdf PS: in this example I use a specific analog sensor, when you want to use another just change the 3 bits used for selecting the analog sensor

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1. include "mbed.h"

SPI spi(p5, p6, p7); mosi(out), miso(in), sclk(clock) DigitalOut cs(p8); cs (the chip select signal)

Serial pc(USBTX, USBRX); tx, rx ( the usb serial communication )

int main() { Setup the spi for 7 bit data, high steady state clock, second edge capture, with a 1MHz clock rate spi.format(7,0); spi.frequency(1000000);

notify the user that we are starting with the ADC communication pc.printf("Starting ADC interaction\n");

lets just do this forever while (1) {

Select the device by seting chip select low cs = 0;

sending the 5 bits + 2 bits to ignore the null bits coming from the device, so the data that is sent is 1100000 spi.write(0xC0);

now the device sends back the readings 12 bits, 7 bits at a time int adc2 = spi.write(0x00); int adc3 = spi.write(0x00);

now we have to mask out the right bits 31 in binary is 00011111 int mask = 31;

we only want the 5 bits from the second reading not 7 as recived adc3 = mask & adc3;

we shift and or the result together int value = ( adc2 << 5 ) | adc3;

and voila we have the value and we can print it for the user pc.printf("WHOAMI register2 = %u\n", value);

Deselect the device cs = 1;

delay some time before reading again wait(1); } }