Nuts and Volts - August 2012

Fritzing session! I searched a bit further and found a more recent version of that file and it worked just fine. Lesson: You might have to mess around a bit to find these parts, and they might not work. (This is just one of the joys of open source design.)

Now, notice in Figure 16 that the part selector box shows ‘MHz’ which probably means the author of this part reused an image (since the price is right, we won’t fault him). The part itself looks like the watch crystal we will be using, so we drag it over to the DS1307 and drop it onto pins 1 and 2. Unfortunately it covers the IC and blocks most of the breadboard connections for pins 7 and 8, so let’s flip the part around 180º as shown in Figure 17.

The Inspector Window

■ FIGURE 15. Typical operating circuit.

have proven necessary often enough in the past that I just throw one in for every digital IC and sleep better.] So, based on Figure 15 and the datasheet specifying the crystal, the next thing I wanted was a 32.768 kHz watch crystal to use on the breadboard. So, I imported “CRYSTAL – kHz.fzpz” as before and it almost killed my

■ FIGURE 16. Select and move the crystal.

Boy howdy! Am I embarrassed! I was writing this tutorial on the fly while learning to use Fritzing, and after all that rigamarole about how to import a DS1307 since they only have a DS1302, I find I was wrong, wrong, You select a DS1302 from the parts bin and drop it on the breadboard, then (as shown in Figure 18a) you open the ‘variant’ dropbox and click on DS1307. Voilà! You have the correct part. We repeat this pattern when we add the resistors (shown in Figure 18b rotated as with the crystal). The default is 220 ohms, but you can click on the resistance dropbox in the resistor’s Inspector window and select 2.2K, which changes both the value and the color bands.

If an exact part you want to use is not in the parts bin, you may find a similar part can be modified in the Inspector window to match your needs. If the exact part you need just isn’t available, the folks at Fritzing will create a part for you (for a fee, of course).