The 1668 is only available in small and “OMFG thats small.” I chose the QSOP16 package. To facilitate breadboarding, I’m using a prototyping adapter from epboard. you stick the chip to the board with flux, and then solder down one corner, then the next … then you smear some solder paste on the pins and run your iron across them. A little practice and you’ll have no bridges and no excess solder all over.

The probe is serial interfaced using SMBUS … its not fully I2C compliant since it doesn’t support 400khz, but it’s kinda slow reading the temps, so 400khz wouldn’t be of any benefit. SMBUS makes it a snap to connect to a microcontroller. The MCU I’m using is the Microchip PIC18F452 … its running at 20 mhz and has all sorts of ports, I’m using two… the hardware serial port (USART) for talking to my desktop and the hardware master synchronous serial port (MSSP) for handling the smbus.

SMBus requires pull-up resistors on its clock and data lines, so they are active low. I have a pair of 10k ohm resistors permantly installed on my pic development board… one on top, one underneath. They can be enabled and dispabled by jumpers. I’ve also soldered a row of header pins to my board, to make interfacing with the pic super easy. In the upper right of the above picture, you can see a MAX232 line level converter, taking the CMOS / logic level signals of the pic and kicking them up a notch to the TTL levels the serial port expects. I imagine the port on my desktop is probably logic level compatible, but, the max232 is there, so i use it.

The breadboard is real simple. I have a filter cap for the power, and one for the diode temperature sender. The other connections are power and SMBUS.

Above is a temperature probe being assembled. In order to connect an NPN transistor as a diode, you need to short the base and collector. I just smashed the pins together with pliers and then soldered on my wire. The emitter is left unmolested.

As you can see, PVC heat shrink tubing sucks … I later found my irradiated poly-olefin heatshrink, which takes the heat a lot better, and actually shrinks when you heat it, instead of just melting and burning.

Heres my little transistor, all soldered up. I put the outer insulation jacket of my wire back around the inner wires, and then slide on some larger diameter shrink to seal everything up.

That one I didn’t do such a clean job on, but it should last a while. I’m thinking for a ‘finished product’ I’ll seal these probes inside BIC Pen caps with some thermal epoxy… that way they’ll be water proof and well protected.

Here is a Molex KK type pin loaded into my crimp-all. A quick squeeze gets you this:

The diode connections and the ground each get a pin, and slide into some 3 position molex kk type connector housings.

Stay tuned for more on this project… I plan to interface it with a huge VFD display, as well as use a smaller and cheaper pic microcontroller.

Ah yes – This will be FUN project … a taste of things to come:

Thats a big, old, obsolete Noritake VFD … it is about 10 inches wide… 20×2, serial interface 9600 bps (it can do 19200 but flickers something awful).

Now to work on some screens and a user interface … hmm this should be interesting.