Breakout Bonanza and DS1307 Realtime Clock

As if I didn’t have enough things on my “to try when I have the time” list already, I recently did a little shopping in both Adafruit and SparkFun. Both had several nifty breakout boards available that promised to speed up and streamline my breadboard projects a lot. In addition to some SMD breakouts that are still in their sealed bags, here’s what I got:

I had a lot of fun soldering the breadboard headers to these little guys. Many are for future projects, like the frequency generator which I’m planning to use for some RFID experiments, and some are just to avoid stripping apart stuff like the connector breakouts. As today’s main topic, I’m covering the DS1307 realtime clock (RTC) breakout in more detail. If you are interested in some of the other items, drop me a comment and I’ll get back to it!

DS1307 Realtime Clock

A realtime clock is simply something that keeps record of the time. Usually, these types of clocks are paired with a small coin cell battery that enables them to keep on counting even if the rest of the circuit is powered of. Such is the case with this breakout, too. Adafruit has an excellent tutorial covering the assembly of this device, all you need is some solder and an iron.

After getting it together, it took me a while to get it working. I used Bus Pirate to communicate with the chip, with the following connections:
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Logic analysis with Bus Pirate

While preparing for my SD tutorial, I realized it would be a long, uphill battle to debug SPI communications with a two-channel oscilloscope, especially when I had no prior experience on implementing SPI with AVR. To break the learning curve to manageable steps, I decided to get a Bus Pirate, a serial protocol tool I had heard a lot of good things about. What made the decision even easier was the fact that my local electronics supplier had just started selling the SparkFun version of Bus Pirate.

In this compact post, I’ll discuss my first impressions of the Bus Pirate, and try out the logic analyzer functionality.

Bus Pirate General Impressions

The first thought that crossed my mind when I saw the Bus Pirate in real life was how small the device was. As you can see, it’s hardly larger than an SD card. All the components are of surface mount type, LEDs included. USB cable was not included but fortunately I had several in my cable drawer. The thing does not need any other setup than plugging it in and installing the FTDI virtual COM port drivers. After that, it showed up as COM19 and I could connect to it with Putty. See the Bus Pirate 101 tutorial for installation details.

The v3 hardware is based on a PIC chip running at 3.3 volts and it took me a while to get comfortable with the power supply & pullup resistor logic – basically you can either use the Bus Pirate pins “normally” so an output pin is driven by the PIC, or in “open drain” mode, where a CD4066B analog switch connects the lines via pullup resistors to whatever is wired to the Vpu pin. This way, the Bus Pirate can interface with other than 3.3V devices (the PIC only pulls the line down or “lets it go” and the pullup takes the line high).
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