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| What is Electromagnetic Education? |
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| – deconstructing the PDA cradle – | |||||||||||||||||||||||||||||||||||||||||||||||||||
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A major difference between the early 'electronic organizers' and later personal digital assistants (PDAs) was the new ability to transfer and synchronize data between a personal computer and the PDA device. A large part of this revolves around personal information management (PIM) software with contacts, calendars, and to-do lists, in addition to the uploading or downloading of information from each device (PC->PDA, and PDA->PC) including custom software. Of the increasingly many methods to do this, the 'synchronization cradle' has been a standard (in addition to infrared, etc.). In the Handspring ™ PDA this system can be seen to consist of a series of eight metallic strips on the bottom edge of the PDA itself, largely invisible when the device is in use. Yet, when matched with the 'hotsync' ™ cradle, these strips match up with those on the cradle and enable the data transfer processes to begin.
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TO do so requires placement of the PDA in the cradle, matching the metallic strips with the eight metallic contacts emerging from the plastic cradle. The cradle itself is itself plugged into a personal computer by way of a data and-or power cable, in the examples here USB 1.1 (universal serial bus) or Serial port plugs are shown. This, then, is the route of the data on the PDA, which through electricity and the transference of electrical power and electrical information, makes its way to and from a PDA through contacting these metallic pins (which are electrical conductors, enabling the easy flow of electricity) which then travels through such cabling by way of the energy of material atoms, to send information throughout this conduit. To start this process, the cradle has a single button, which when depressed begins the process of 'syncing' PDA with PC, and in doing so, connecting the hardware and software of the these two devices with each other, through the electronics of this cradle. The external interface of the synchronization cradle is so simple, though to uncover its external shell is to see in more detail how this process can be seen to work in the artifact.
WHEN uncovering the cradle, there is a direct relation between the eight external metallic strips on the PDA, and those (also large) strips inside the PDA's cradle. They are a perfect match and complementary in design. These eight strips lead into a very small circuit board where each metal strip becomes a pathway into a small chip, the SIPEX SP3232ECT which will be referred to again shortly. By searching for datasheets online, this function of this chip can be identified as a 'line transceiver' which transmits and receives signals, and uses electricity to do so. Throughout the integrated circuitry of this chip, data is exchanged and routed back out through a miniature network of metallic wiring or pathways in the circuitboard, which are externalized and made visible in the multi-colored wires sprouting from the PCB (printed circuit board) which then are brought into a single cable which becomes is then terminated at its far end by a Serial plug connector. | |||||||||||||||||||||||||||||||||||||||||||||||||||
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WHAT is interesting to note is that of the eight metallic strips on both the PDA and cradle, the Serial port has nine holes (which are interfaces for nine individual electrical wires) -- while the wires sprouting for a connection for a PDA and PC consist of only six wires, that is two less than the metallic strips on the PDA and its cradle, which could be used instead to provide power, and three wires less than the Serial port connector allows. What can be assumed is that six wires provide all the necessary power and information transfer needs.
ALSO of interest is to see what on the external PDA cradle is a nicely molded custom plastic button with its own customized grotto-like enclave which makes room for a human finger to easily press and depress the button to start the process of hardware and software synchronization. When looking at the circuit board, this customized button on the industrial-design interface becomes a non-descript and altogether ordinary electronics component, a commonplace button which is seen towards the bottom of the PCB as a metallic square with white circle at its center. This button has the tactility and feedback (bounce) that can be felt on the exterior, a quality of reflex (the button pushes back when depressed and responds with a click-like verification that can be felt in the hand). It is such changes from inside to outside that can be universally seen in electronics upon their opening up - that even the most advanced electronics use tried-and-true design methods to make things work well, as intended. Though this may not mean reinventing a good button on a circuit board, as much as providing an interface to types of buttons with form-factors conducive to its interaction. Also of note is that the printed circuitboard is copyrighted (©2000). WITH a little bit of information-archaeology or electromagnetic-archaeology one can discover even more about this device without being an electronics expert. By searching online for the datasheet (.pdf) of the specific chip (SIPEX SP3232ECT) at the company's website, one can find the schematics of the functioning of the specific chip, its process, and possibly why the design decisions on the circuit board resulted in eight metal contacts for data and power transfer yet only 6 for the serial port connection. Those with some understanding of electronics circuits will likely be able to 'read' more into such decisions based on knowledge and literacy, yet it should not stop others who have interest from investigating this further, as it is accessible to all. | |||||||||||||||||||||||||||||||||||||||||||||||||||
Pinout configuration for the SIPEX SP3232ECT chip from datasheet Educational fair-use, electronetwork.org 2004 |
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LOCATING the sp3222_3232e.pdf for the chip reveals it as a 'True +3.0V to +5.5V RS-232 Transceiver.' Meaning, it operates within positive 3.0-5.5 Volts with a standard serial port connection (RS-232) for hardware and software flow control. Its maximum data throughput is 9600 bits per second (bps) at a distance of 15 meters (roughly 50 feet), which most likely relates to power and data issues. The datasheet description of the chip states that it is "intended for portable or handheld applications such as notebook or palmtop computers." What makes the specific chip model 'ECT' meaningful is that it specifies the chip is uniquely able to operate in a temperature range of 0 to +70 degrees Celsius and exists in a 16-Pin WSOIC package type, known as a (wide) small outline integrated circuit.
IN order to make sense of the above graphic representation, a quick reference table helps decipher the specific functions of the integrated circuit (IC).
LIKEWISE, mapping the pins to the circuit diagram of a specific chip helps to conceptualize what is happening beneath its often impenetrable surface. That is, how the device operates the way it does, to perform its designed functions. The logic inputs and outputs and their relation to (serial) RS-232 connections are visibly identifiable in electronic symbols and specifications. | |||||||||||||||||||||||||||||||||||||||||||||||||||
Typical Operating Circuit for the SIPEX SP3232ECT chip from datasheet Educational fair-use, electronetwork.org 2004 |
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The 'triangle with circle on its tip' indicates an 'invertor' logic gate made of transistors (TTL). Beside it is a 5k ohm resistor. Pins one through six consists of capacitors of 0.1 microfarad which relate to the 'charge-pump' as described in the Device Pin Description table. This may also relate to what the datasheet describes as the ESD Test Circuit for Human Body Model which uses resistors and capacitors to reduce the unpredictability of the Electrostatic Discharge arc. As stated: "In situations such as hand held systems, the ESD charge can be directly discharged to the equipment from a person already holding the equipment. The current is transferred on to the keypad or the serial port of the equipment directly and then travels through the PCB and finally to the IC." This would seem to indicate that even the dangers of electrostatic discharge (sparks) to human or electronics machinery is prepared to be absorbed by the chip itself, as part of its design. To do so, the value of each element would be specifically chosen to manage this task.
ALL in all, it is hoped by taking apart a seemingly simple PDA cradle that the world of electronics hidden underneath offers a glimpse of its significance to making things work the way they do, and that a unique and basic understanding can be achieved through deconstructing such basic devices. Please make note that it is very important to know some basics about electronics safety before taking things apart, and then only certain objects would probably be worthwhile or safe to dismantle without additional knowledge which may be beyond novice learners. In any case, from the chip to the circuit board to the wires, cables, and plugs, to the machines it interface, the PDA cradle offers insight into how electronics tie together both hardware and software in their design, to make things happen. (bc 8.15.2004) |
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