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Issue #204 July 2007
Pyxos Power
by Tom Cantrell
Start | LAN-In-the-Box |Down to the Wire | Variable Interest | Hook 'Em Danno |Build it and they will come | Match point | Sources and PDF
HOOK ’EM DANNO
When it comes to understanding the range of Pyxos FT possibilities, a picture is worth a thousand words, so let’s take a closer look. At $399, the Pyxos FT kit isn’t an impulse buy, but you do get a significant amount of gear (see Photo 1). Here’s the rundown.
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| Photo 1—The Pyxos FT evaluation kit includes boards covering the likely application spectrum. Starting at the bottom right is the ARM7 MCU-based Pilot with USB (or optional LonWorks) connection to a host PC. Headed clockwise you see an ARM7 MCU-based actuator Point, an AVR MCU-based sensor Point, and an unhosted Nano Point. |
Not unexpectedly, the Pilot, using an Atmel ARM7-based flash MCU, is the largest and most complicated board. Besides handling the Pilot duties, it also supports USB and/or LonWorks (the orange connector) connections to a host PC.
Next up is the “Accuator Point,” which, using the same ARM7-based MCU as the Pilot, demonstrates an example of a “high-performance” Point. In addition to the complement of digital I/O that every board includes (i.e., lights and switches), it includes an ADC for capturing an analog input voltage.
Moving down the ladder of cost and complexity, we find the “Sensor Point,” which uses an Atmel TinyAVR 8-bit, eight-pin MCU. Befitting its name, in addition to the lights and switches, it includes temperature and light-level sensors as well as an analog voltage output.
Finally, we come to the ”NanoPoint,” which is an example of an “unhosted Point” (i.e., one that just uses the Pyxos FT chip by itself without a host MCU). In the latter configuration, the five pins used for the host MCU interface in “Hosted Point” mode are used instead as digital I/O to directly control attached devices, in this case the NanoPoints own complement of lights and switches.
A significant portion of the board space and circuitry you see is associated with the use of the 24-VAC link power option. Keep in mind that a minimal (i.e., nonisolated, common power supply) nonlink powered Point could consist of little more than the Pyxos FT chip and its required 10-MHz crystal. Also note that while the crystal is required, at least there’s the option to drive the 10-MHz clock waveform out of one of the Pyxos FT chip pins for use by other logic (e.g., a host MCU).
Software that comes with the kit includes a show and tell human-machine interface (HMI) application. The HMI demo centers around a screen representation of the entire network and the functions associated with each device (see Photo 2). For example, pushing a button on one of the Points causes both a “real” LED on the Pilot board, and the associated “virtual” LED on the HMI screen, to light at the same time.
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| Photo 2—The human-machine interface (HMI) demo application centers on a visual representation, which along with an activity log, allows monitoring transactions between devices attached to the network. |
Referring again to Photo 1, notice the small twisted pair (red and black) cable between the Sensor and Actuator Point boards. This cable connects the output DAC on the former to the input ADC on the latter. The HMI software includes a “Performance Demo,” which is a loopback test that has the Pilot commanding the Sensor Point to output a voltage, which the Actuator Point in turn captures, converts, and publishes back to the Pilot.
The kit also includes the source code for the Pilot and Point APIs and, as mentioned earlier, the Pilot is quite a bit more complex. But, it’s all relative considering the Point API requires less than 1 KB while the Pilot calls for a “whopping” 6 KB or so. Note that minimal hosted Point applications have the option of reducing host MCU overhead even further by dismissing the API altogether and simply driving the Pyxos FT chip directly. And of course there’s no MCU overhead (because there’s no MCU) in “nonhosted Points.”
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