Nuts and Volts - January 2008

The PIC18F2685’s ADC module is capable of resolving 10 bits of resolution. That is equivalent to 1024 steps

LISTING 3

including zero. The PIC18F2685’s ADC is referenced to the supply voltage according to the cleared bits in the upper nibble of the ADCON1 register value. So, that means every step of the PIC18F2685’s ADC will represent approximately 0.005 volts. That means that 1°C is equal to two ADC steps. So, to get an absolute temperature result we need only to read the ADC and divide by two. In the code that follows, I read the AD594’s output 20 times, take the average of the 20 readings, and divide the average by two (see Listing 2).

Nothing to it. Now that you know how to make an AD594 work for you, I’ll show you one that is ready for action in Photo 5.

dataLen = 4;                 //length of CAN message
id = brd_display_temp_id;     //sender’s CAN ID
data[0] = addr_ad594;         //destination CAN ID
//the CAN message contains this data:
data[1] = temp_in_C;
data[2] =  make8(temp_in_C,1); // high byte
data[3] = make8(temp_in_C,0);  //low byte
while(!ECANSendMessage(id, data, dataLen, ECAN_TX_STD_FRAME));

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Yep. You’re trained. The next time you tackle what seems to be a difficult embedded project, just kick back and think of the I/O basics you need to accomplish each individual task. Once you’ve worked out the fundamentals, merge all of the solutions together to complete the system’s mission.

I’ll leave you with something to consider. How would you send the AD594 data to another PIC-based computing node? Listing 3 shows how I did it.

Yes you CAN! Put another notch in your soldering iron. NV

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SOURCES

■ Microchip

( www.microchip.com): PIC18F2685

■ Analog Devices

( www.analogdevices.com): AD594

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