http://nerdswithoutborders.net/index.php?title=Turtle_Sense_Smart_Sensor_board_v.0.46&feed=atom&action=historyTurtle Sense Smart Sensor board v.0.46 - Revision history2024-03-28T16:43:25ZRevision history for this page on the wikiMediaWiki 1.35.5http://nerdswithoutborders.net/index.php?title=Turtle_Sense_Smart_Sensor_board_v.0.46&diff=548&oldid=prevDave: /* Transceiver */ Edited for description of phase 3 new circuit2016-07-01T01:56:55Z<p><span dir="auto"><span class="autocomment">Transceiver: </span> Edited for description of phase 3 new circuit</span></p>
<table class="diff diff-contentalign-left diff-editfont-monospace" data-mw="interface">
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">← Older revision</td>
<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 01:56, 1 July 2016</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l12" >Line 12:</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>The accelerometer sensor IC (U2) is an [http://dlnmh9ip6v2uc.cloudfront.net/datasheets/BreakoutBoards/ADXL362.pdf Analog Devices ADXL362]. The accelerometer measures the forces (including gravity) acting on it in 3 axes, and also temperature. The IC is extremely low powered and low noise. The microprocessor controls an analog switch (U4) which switches the 3.3V power going to the accelerometer. 3.0V power is supplied to the chip from the microprocessor I/O pin P2.7. The accelerometer has two power inputs, labeled Vio and Vs. Vio is the power for the digital circuitry, and Vs powers the low level analog circuitry. Vs is filtered from any digital noise on Vio by R7 and C7. The accelerometer communicates with the microprocessor via a standard 4-wire SPI interface. These four signals are labeled /CS, CLK, MOSI, and MISO. In addition the accelerometer has two interrupt lines (INT1 and INT2) going to the microprocessor.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>The accelerometer sensor IC (U2) is an [http://dlnmh9ip6v2uc.cloudfront.net/datasheets/BreakoutBoards/ADXL362.pdf Analog Devices ADXL362]. The accelerometer measures the forces (including gravity) acting on it in 3 axes, and also temperature. The IC is extremely low powered and low noise. The microprocessor controls an analog switch (U4) which switches the 3.3V power going to the accelerometer. 3.0V power is supplied to the chip from the microprocessor I/O pin P2.7. The accelerometer has two power inputs, labeled Vio and Vs. Vio is the power for the digital circuitry, and Vs powers the low level analog circuitry. Vs is filtered from any digital noise on Vio by R7 and C7. The accelerometer communicates with the microprocessor via a standard 4-wire SPI interface. These four signals are labeled /CS, CLK, MOSI, and MISO. In addition the accelerometer has two interrupt lines (INT1 and INT2) going to the microprocessor.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>==Transceiver==</div></td><td class='diff-marker'>+</td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>==<ins class="diffchange diffchange-inline">Coax </ins>Transceiver==</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>The Smart Sensor has <del class="diffchange diffchange-inline">an </del>[http://www.<del class="diffchange diffchange-inline">analog</del>.com/<del class="diffchange diffchange-inline">static</del>/<del class="diffchange diffchange-inline">imported-files</del>/<del class="diffchange diffchange-inline">data_sheets</del>/<del class="diffchange diffchange-inline">ADM3483_3485_3488_3490_3491</del>.pdf <del class="diffchange diffchange-inline">ADM 3483 RS485 transceiver </del>IC] <del class="diffchange diffchange-inline"> </del>(<del class="diffchange diffchange-inline">U2</del>) identical to the <del class="diffchange diffchange-inline">one </del>on the Comm <del class="diffchange diffchange-inline">Board</del>. <del class="diffchange diffchange-inline">The two transceivers send </del>and <del class="diffchange diffchange-inline">receive data </del>over <del class="diffchange diffchange-inline">the sensor </del>cable <del class="diffchange diffchange-inline">as differential twisted pairs</del>. <del class="diffchange diffchange-inline">That </del>is<del class="diffchange diffchange-inline">, there are two wires for transmitting data (labeled Y </del>and <del class="diffchange diffchange-inline">Z on </del>the <del class="diffchange diffchange-inline">transceiver), and two wires for receiving data </del>(<del class="diffchange diffchange-inline">labeled A and B on the transceiver</del>). The <del class="diffchange diffchange-inline">reason for this is </del>to <del class="diffchange diffchange-inline">improve noise immunity on </del>the <del class="diffchange diffchange-inline">cable and to allow faster data rates</del>. <del class="diffchange diffchange-inline"> Note that </del>the <del class="diffchange diffchange-inline">data pairs are crossed between the two transceivers - that is, </del>the <del class="diffchange diffchange-inline">send pair on one transceiver </del>is <del class="diffchange diffchange-inline">connected to </del>the <del class="diffchange diffchange-inline">receive pair on the other transceiver</del>. The <del class="diffchange diffchange-inline">communication uses standard RS485 </del>UART <del class="diffchange diffchange-inline">protocol at 115</del>,<del class="diffchange diffchange-inline">200 baud</del>. <del class="diffchange diffchange-inline">A resistor (R8) is </del>a <del class="diffchange diffchange-inline">termination resistor on </del>the <del class="diffchange diffchange-inline">receive inputs </del>of <del class="diffchange diffchange-inline">U2 </del>in <del class="diffchange diffchange-inline">order to prevent </del>signal <del class="diffchange diffchange-inline">reflections travelling back to the Comm Board transceiver outputs</del>. The <del class="diffchange diffchange-inline">RS485 Transceivers in </del>the <del class="diffchange diffchange-inline">circuitry are capable of driving </del>a <del class="diffchange diffchange-inline">signal through several hundred feet of cable</del>. <del class="diffchange diffchange-inline"> However</del>, the <del class="diffchange diffchange-inline">response timing in </del>the <del class="diffchange diffchange-inline">program may need to be adjusted if long lengths of cable are used</del>.</div></td><td class='diff-marker'>+</td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>The Smart Sensor has <ins class="diffchange diffchange-inline">a </ins>[http://www.<ins class="diffchange diffchange-inline">ti</ins>.com/<ins class="diffchange diffchange-inline">lit/ds/symlink/sn74lvc1g240.pdf SN74LVC1G240 driver IC] (U4) and a [http:/</ins>/<ins class="diffchange diffchange-inline">ww1.microchip.com/downloads/en</ins>/<ins class="diffchange diffchange-inline">DeviceDoc</ins>/<ins class="diffchange diffchange-inline">21696H</ins>.pdf <ins class="diffchange diffchange-inline">MCP6541 receiver </ins>IC] (<ins class="diffchange diffchange-inline">U3</ins>)<ins class="diffchange diffchange-inline">, </ins>identical to the <ins class="diffchange diffchange-inline">ones </ins>on the Comm <ins class="diffchange diffchange-inline">board</ins>. <ins class="diffchange diffchange-inline">Communication </ins>and <ins class="diffchange diffchange-inline">3.0V DC power are </ins>over <ins class="diffchange diffchange-inline">a single wire (RG6 75 ohm coax </ins>cable<ins class="diffchange diffchange-inline">)</ins>. <ins class="diffchange diffchange-inline">The DC power </ins>is <ins class="diffchange diffchange-inline">isolated from the AC serial communication signal by a bias T consisting of L1 </ins>and <ins class="diffchange diffchange-inline">C8.</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div> </div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">The microprocessor sends a 1 MHz signal to the input of </ins>the <ins class="diffchange diffchange-inline">driver </ins>(<ins class="diffchange diffchange-inline">U4</ins>). The <ins class="diffchange diffchange-inline">microprocessor also sends a serial 115 kilobaud UART signal </ins>to the <ins class="diffchange diffchange-inline">Enable input of the driver</ins>. <ins class="diffchange diffchange-inline">Thus </ins>the <ins class="diffchange diffchange-inline">output of </ins>the <ins class="diffchange diffchange-inline">driver </ins>is <ins class="diffchange diffchange-inline">a 1 MHz signal modulated by </ins>the <ins class="diffchange diffchange-inline">UART signal</ins>. The <ins class="diffchange diffchange-inline">driver output is capable of driving at least 400' of RG6 cable.</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div> </div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">Serial </ins>UART <ins class="diffchange diffchange-inline">signals are received by U3, which acts as a comparator. The non-inverting input filters the rectified incoming signal on the wire with a time constant of about 1 msec</ins>, <ins class="diffchange diffchange-inline">which is a little longer than one byte of data</ins>. <ins class="diffchange diffchange-inline">The non-inverting input also has </ins>a <ins class="diffchange diffchange-inline">small DC bias added to keep </ins>the <ins class="diffchange diffchange-inline">output </ins>of <ins class="diffchange diffchange-inline">the comparator </ins>in <ins class="diffchange diffchange-inline">the correct state (logic high) when no </ins>signal <ins class="diffchange diffchange-inline">is being received</ins>. <ins class="diffchange diffchange-inline"> </ins>The <ins class="diffchange diffchange-inline">inverting input of </ins>the <ins class="diffchange diffchange-inline">comparator is filtered with </ins>a <ins class="diffchange diffchange-inline">much shorter 2</ins>.<ins class="diffchange diffchange-inline">7 usec time constant</ins>, <ins class="diffchange diffchange-inline">which removes </ins>the <ins class="diffchange diffchange-inline">1 MHz carrier but retains </ins>the <ins class="diffchange diffchange-inline">individual bit data</ins>.</div></td></tr>
</table>Davehttp://nerdswithoutborders.net/index.php?title=Turtle_Sense_Smart_Sensor_board_v.0.46&diff=547&oldid=prevDave: /* Accelerometer */ Edit for different U numbers and new power source.2016-06-30T23:29:01Z<p><span dir="auto"><span class="autocomment">Accelerometer: </span> Edit for different U numbers and new power source.</span></p>
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 23:29, 30 June 2016</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l10" >Line 10:</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>==Accelerometer==</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>==Accelerometer==</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>The accelerometer sensor IC (<del class="diffchange diffchange-inline">U3</del>) is an [http://dlnmh9ip6v2uc.cloudfront.net/datasheets/BreakoutBoards/ADXL362.pdf Analog Devices ADXL362]. The accelerometer measures the forces (including gravity) acting on it in 3 axes, and also temperature. The IC is extremely low powered and low noise. The microprocessor controls an analog switch (U4) which switches the 3.3V power going to the accelerometer. The accelerometer has two power inputs, labeled Vio and Vs. Vio is the power for the digital circuitry, and Vs powers the low level analog circuitry. Vs is filtered from any digital noise on Vio by R7 and C7. <del class="diffchange diffchange-inline"> The output of U4 is normally connected to the 3.3V switch input. A logic high pulse from the microprocessor connects the 3.3V accelerometer power to ground to reset it. </del>The accelerometer communicates with the microprocessor via a standard 4-wire SPI interface. These four signals are labeled /CS, CLK, MOSI, and MISO. In addition the accelerometer has two interrupt lines (INT1 and INT2) going to the microprocessor.</div></td><td class='diff-marker'>+</td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>The accelerometer sensor IC (<ins class="diffchange diffchange-inline">U2</ins>) is an [http://dlnmh9ip6v2uc.cloudfront.net/datasheets/BreakoutBoards/ADXL362.pdf Analog Devices ADXL362]. The accelerometer measures the forces (including gravity) acting on it in 3 axes, and also temperature. The IC is extremely low powered and low noise. The microprocessor controls an analog switch (U4) which switches the 3.3V power going to the accelerometer<ins class="diffchange diffchange-inline">. 3.0V power is supplied to the chip from the microprocessor I/O pin P2.7</ins>. The accelerometer has two power inputs, labeled Vio and Vs. Vio is the power for the digital circuitry, and Vs powers the low level analog circuitry. Vs is filtered from any digital noise on Vio by R7 and C7. The accelerometer communicates with the microprocessor via a standard 4-wire SPI interface. These four signals are labeled /CS, CLK, MOSI, and MISO. In addition the accelerometer has two interrupt lines (INT1 and INT2) going to the microprocessor.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>==Transceiver==</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>==Transceiver==</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>The Smart Sensor has an [http://www.analog.com/static/imported-files/data_sheets/ADM3483_3485_3488_3490_3491.pdf ADM 3483 RS485 transceiver IC] (U2) identical to the one on the Comm Board. The two transceivers send and receive data over the sensor cable as differential twisted pairs. That is, there are two wires for transmitting data (labeled Y and Z on the transceiver), and two wires for receiving data (labeled A and B on the transceiver). The reason for this is to improve noise immunity on the cable and to allow faster data rates. Note that the data pairs are crossed between the two transceivers - that is, the send pair on one transceiver is connected to the receive pair on the other transceiver. The communication uses standard RS485 UART protocol at 115,200 baud. A resistor (R8) is a termination resistor on the receive inputs of U2 in order to prevent signal reflections travelling back to the Comm Board transceiver outputs. The RS485 Transceivers in the circuitry are capable of driving a signal through several hundred feet of cable. However, the response timing in the program may need to be adjusted if long lengths of cable are used.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>The Smart Sensor has an [http://www.analog.com/static/imported-files/data_sheets/ADM3483_3485_3488_3490_3491.pdf ADM 3483 RS485 transceiver IC] (U2) identical to the one on the Comm Board. The two transceivers send and receive data over the sensor cable as differential twisted pairs. That is, there are two wires for transmitting data (labeled Y and Z on the transceiver), and two wires for receiving data (labeled A and B on the transceiver). The reason for this is to improve noise immunity on the cable and to allow faster data rates. Note that the data pairs are crossed between the two transceivers - that is, the send pair on one transceiver is connected to the receive pair on the other transceiver. The communication uses standard RS485 UART protocol at 115,200 baud. A resistor (R8) is a termination resistor on the receive inputs of U2 in order to prevent signal reflections travelling back to the Comm Board transceiver outputs. The RS485 Transceivers in the circuitry are capable of driving a signal through several hundred feet of cable. However, the response timing in the program may need to be adjusted if long lengths of cable are used.</div></td></tr>
</table>Davehttp://nerdswithoutborders.net/index.php?title=Turtle_Sense_Smart_Sensor_board_v.0.46&diff=546&oldid=prevDave: /* Microprocessor */ Edit for phase 3 newer version of chip.2016-06-30T23:22:04Z<p><span dir="auto"><span class="autocomment">Microprocessor: </span> Edit for phase 3 newer version of chip.</span></p>
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 23:22, 30 June 2016</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* controlling, reading and recording data from the accelerometer IC</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* controlling, reading and recording data from the accelerometer IC</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* uploading data to the Comm Board</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* uploading data to the Comm Board</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>We selected the[http://www.ti.com/lit/ds/symlink/<del class="diffchange diffchange-inline">msp430fr5739</del>.pdf Texas Instruments <del class="diffchange diffchange-inline">MSP430FR5739</del>] because it is extremely low power and contains <del class="diffchange diffchange-inline">16 </del>K of FRAM memory<del class="diffchange diffchange-inline">. Newer versions of this chip contain more memory and will likely be used in future versions</del>. The 3.<del class="diffchange diffchange-inline">3V </del>power from the Comm Board comes into U1 on AVCC and DVCC. The power ground connections are on AVSS and DVSS. There are three 8 bit I/O ports in the chip, labelled P1.0-P1.7, P2.0-P2.7, and P3.0-P3.7. Some of these ports are connected to the accelerometer (<del class="diffchange diffchange-inline">U3</del>) and to the transceiver (<del class="diffchange diffchange-inline">U2</del>)<del class="diffchange diffchange-inline">, and many others </del>are not used. There are two pins connected to an external crystal (X1). X1, along with C1 an C2, provide the chip with a precise 32.768 KHz clock which is used for the timing functions in the program. The chip also has other internal higher frequency clocks. Another set of pins on the chip, labelled J.0-J.3, -RST, and Test, are used for programming the chip. These pins are connected to a PC via the JTAG connector J2. Since the Smart Sensor is cast in polyurethane resin, after it is cast it cannot be programmed again. However, many of the operating parameters can later be changed by downloading them from the Comm Board.</div></td><td class='diff-marker'>+</td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>We selected the[http://www.ti.com/lit/ds/symlink/<ins class="diffchange diffchange-inline">msp430fr5949</ins>.pdf Texas Instruments <ins class="diffchange diffchange-inline">MSP430FR5949</ins>] because it is extremely low power and contains <ins class="diffchange diffchange-inline">64 </ins>K of FRAM memory. The 3.<ins class="diffchange diffchange-inline">0V </ins>power from the Comm Board comes into U1 on AVCC and DVCC. The power ground connections are on AVSS and DVSS. There are three 8 bit I/O ports in the chip, labelled P1.0-P1.7, P2.0-P2.7, and P3.0-P3.7<ins class="diffchange diffchange-inline">, plus three other I/O pins labelled P4.0, P4.1, and P4.4</ins>. Some of these ports are connected to the accelerometer (<ins class="diffchange diffchange-inline">U2), the moisture sensing circuit (C12-13 plus other parts</ins>)<ins class="diffchange diffchange-inline">, </ins>and to the <ins class="diffchange diffchange-inline">coax </ins>transceiver (<ins class="diffchange diffchange-inline">U3 and U4</ins>)<ins class="diffchange diffchange-inline">. Many other I/O pins </ins>are not used<ins class="diffchange diffchange-inline">, but are available on an optional header.</ins>. There are two pins connected to an external crystal (X1). X1, along with C1 an C2, provide the chip with a precise 32.768 KHz clock which is used for the timing functions in the program. The chip also has other internal higher frequency clocks. Another set of pins on the chip, labelled J.0-J.3, -RST, and Test, are used for programming the chip. These pins are connected to a PC via the JTAG connector J2. Since the Smart Sensor is cast in polyurethane resin, after it is cast it cannot be programmed again. However, many of the operating parameters can later be changed by downloading them from the Comm Board.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>==Accelerometer==</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>==Accelerometer==</div></td></tr>
</table>Davehttp://nerdswithoutborders.net/index.php?title=Turtle_Sense_Smart_Sensor_board_v.0.46&diff=545&oldid=prevDave: Start page - needs text editing2016-06-23T03:55:22Z<p>Start page - needs text editing</p>
<p><b>New page</b></p><div>Smart Sensor v.0.46 is the sensor board which connects to the main [[Turtle Sense communications board v.0.43|Communications Board]]. The Smart Sensor contains a microprocessor, an accelerometer sensor IC, and a Transceiver IC.<br />
* [[Turtle Sense Smart Sensor PCB Schematic v.0.46|PCB schematic]]<br />
<br />
==Microprocessor==<br />
The microprocessor (U1) is identical to the one on the Comm Board. It controls all the operation of the device. Programmed in C, it manages all the circuitry by:<br />
* timing events<br />
* controlling, reading and recording data from the accelerometer IC<br />
* uploading data to the Comm Board<br />
We selected the[http://www.ti.com/lit/ds/symlink/msp430fr5739.pdf Texas Instruments MSP430FR5739] because it is extremely low power and contains 16 K of FRAM memory. Newer versions of this chip contain more memory and will likely be used in future versions. The 3.3V power from the Comm Board comes into U1 on AVCC and DVCC. The power ground connections are on AVSS and DVSS. There are three 8 bit I/O ports in the chip, labelled P1.0-P1.7, P2.0-P2.7, and P3.0-P3.7. Some of these ports are connected to the accelerometer (U3) and to the transceiver (U2), and many others are not used. There are two pins connected to an external crystal (X1). X1, along with C1 an C2, provide the chip with a precise 32.768 KHz clock which is used for the timing functions in the program. The chip also has other internal higher frequency clocks. Another set of pins on the chip, labelled J.0-J.3, -RST, and Test, are used for programming the chip. These pins are connected to a PC via the JTAG connector J2. Since the Smart Sensor is cast in polyurethane resin, after it is cast it cannot be programmed again. However, many of the operating parameters can later be changed by downloading them from the Comm Board.<br />
<br />
==Accelerometer==<br />
The accelerometer sensor IC (U3) is an [http://dlnmh9ip6v2uc.cloudfront.net/datasheets/BreakoutBoards/ADXL362.pdf Analog Devices ADXL362]. The accelerometer measures the forces (including gravity) acting on it in 3 axes, and also temperature. The IC is extremely low powered and low noise. The microprocessor controls an analog switch (U4) which switches the 3.3V power going to the accelerometer. The accelerometer has two power inputs, labeled Vio and Vs. Vio is the power for the digital circuitry, and Vs powers the low level analog circuitry. Vs is filtered from any digital noise on Vio by R7 and C7. The output of U4 is normally connected to the 3.3V switch input. A logic high pulse from the microprocessor connects the 3.3V accelerometer power to ground to reset it. The accelerometer communicates with the microprocessor via a standard 4-wire SPI interface. These four signals are labeled /CS, CLK, MOSI, and MISO. In addition the accelerometer has two interrupt lines (INT1 and INT2) going to the microprocessor.<br />
<br />
==Transceiver==<br />
The Smart Sensor has an [http://www.analog.com/static/imported-files/data_sheets/ADM3483_3485_3488_3490_3491.pdf ADM 3483 RS485 transceiver IC] (U2) identical to the one on the Comm Board. The two transceivers send and receive data over the sensor cable as differential twisted pairs. That is, there are two wires for transmitting data (labeled Y and Z on the transceiver), and two wires for receiving data (labeled A and B on the transceiver). The reason for this is to improve noise immunity on the cable and to allow faster data rates. Note that the data pairs are crossed between the two transceivers - that is, the send pair on one transceiver is connected to the receive pair on the other transceiver. The communication uses standard RS485 UART protocol at 115,200 baud. A resistor (R8) is a termination resistor on the receive inputs of U2 in order to prevent signal reflections travelling back to the Comm Board transceiver outputs. The RS485 Transceivers in the circuitry are capable of driving a signal through several hundred feet of cable. However, the response timing in the program may need to be adjusted if long lengths of cable are used.</div>Dave