S.N.A.K.E.: A Dynamically Reconfigurable Artificial Sensate Skin ...

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arbitrarily assigned. In the specific case of the Skin Patch assembled to test the project, 12 nodes were connected and addresses 0x100–0x10A were assigned, to consequent nodes. Now, all nodes are first loaded with the Bootloader program described before, however what was not mentioned before is that when the Bootloader is programmed using the JTAG debugger, the I 2 C address assigned to the node is assembled into location 0x1080 in flash memory. This is done so that I 2 C addresses are only assigned once in the programming lifetime of the nodes, and no conflicts are created in the bus. If two nodes with the same address are placed on the same bus, the system will eventually reach a deadlock state which must be manually reset, which is why it is so critical to avoid this situation. The solution to the last question, ”How is the bus arbitrated?” is actually really simple: the MSP430 does it. The I 2 C hardware module of the MSP430 microcontroller, can detect collisions in the bus and has a method to resolve contentions. Whenever a collision is detected, the device that first takes the data line to ground loses arbitration and an interrupt flag is generated. Processing this interrupt flag allows communications to remain reliable. These cases are rare though, as only one master exists in every Skin Patch: the Brain. The last consideration to make about the I 2 C backbone bus is the speed at which it is run. This is the second parameter that limits the amount of nodes that can be connected to the same patch. Although bandwidth requirements are supposed to be brought down with the addition of processing power into each node, there is still the need to transfer either higher-order features into a PC, or simple raw data if the Skin Patch is to be used as a data extraction device. The amount of bandwidth needed will depend on a variety of factors, like the number of nodes, the sampling rates, and the resolution at which each sensor is sampled. Making the bus run at fast-speed (3.4Mbps) would have placed huge constraints on the length of the bus lines, and running it at the standard speed of 100Kbps would not have been enough for more than a couple of nodes. Therefore high-speed mode was chosen, and the bus is then run at 400Kbps 13 . 13 Although these are the standard speeds of the I 2 C standard, the I 2 C module of the MSP430 can run the bus at any arbitrary speed, up to a limit of close to 500Kbps 102
4.3.2 Peer to Peer Peer to peer communication was added to every node so that data could be exchanged between them without the need to use the backbone bus, which is only to be used for data transfer between a Brain and the Patch Network. With this, it is possible to combine data from each node’s own sensors with that of adjacent ones so that more information can be extracted across the footprint of a stimulus event, and either sampling rates can be adjusted, or features like center of mass and sound directionality can be calculated. No application currently developed for the system utilizes this capability, however this is mentioned before for two reasons: first, because it is part of the design of the system, and second because it sets the basis for future applications and algorithms. One of these possible algorithms is precisely a Network discovery algorithm, which is critical for a Skin Patch that can be assembled an disassembled. Our current project has a fixed number of nodes in a known topology, so all the software developed for the PC and most of the firmware was created knowing beforehand the configuration of the Skin Patch network. Yet, for the more general case in which the number of nodes, and the way they are connected is not known a priori, a method must be provided so that the Brain firmware and PC software can identify how a particular Skin Patch is connected. The algorithm may look something like this: 1. Every Brain should ping all the addresses to find out which nodes are present 2. For every node in present, the brain will obtain a neighbor list 3. Once a list with all nodes is created, a routing table is generated 4. With the routing table generated, all P2P links can be established and the topology of the Skin Patch Network is found An alternate way of doing this would be to have each node report itself to the Brain once it is connected, however this would need the I 2 C bus to work as a multiple master bus. This is actually possible but, once again it is left as a future enhancement to the project. 103
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Author S.N.A.K.E.: A Dynamically Re
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S.N.A.K.E.: A Dynamically Reconfigu
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Table of Contents Abstract 3 Acknow
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List of Figures 2-1 Created by MIT
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E-1 OpenGL Control Header File . .
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Chapter 1 Introduction “Imaginati
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The current project, named S.N.A.K.
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Hardware Each Skin Patch is compose
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living tissue. Particularly in the
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Figure 2-2: Leonardo’s Hand great
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Artificial Sensate Skins elsewhere
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2.1.2 Ultra-dense Sensor Arrays Thi
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2.2 Flexible Circuits Although, not
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2.2.2 Other Technologies Figure 2-6
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human skin. The following design pr
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(a) Skin Patches as data extraction
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Figure 3-3: I 2 C Routing pattern T
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3.2.2 Peer to Peer As we already me
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5. Audio: by adding a MEMS micropho
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Table 3.1: Material thicknesses and
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(a) Node Front (b) Node Back Figure
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Figure 3-9: Skin Patch mechanical t
Page 52 and 53: used, which only further complicate
Page 54 and 55: 8. Teardrops and filleting were add
Page 56 and 57: (a) 7.4V, 2.2mAh Li-ion Battery (b)
Page 58 and 59: in more detail in the Results Chapt
Page 60 and 61: has a 30mA forward current with a f
Page 62 and 63: Figure 3-14: Strain gage layer prot
Page 64 and 65: an unbalanced Wheatstone bridge, fr
Page 66 and 67: Figure 3-16: QTC response curve for
Page 68 and 69: (a) Prototype boards used to calibr
Page 70 and 71: whisker is epoxied to the package o
Page 72 and 73: Sound The only sensing modality add
Page 74 and 75: Figure 3-20: Brain regular PCB fabr
Page 76 and 77: 3.4.3 Communications unit The Commu
Page 79 and 80: Chapter 4 Software “A Scientist d
Page 81 and 82: Networks. Why is this relevant? Mai
Page 83 and 84: Figure 4-1: Bootloader memory map C
Page 85 and 86: Bit Flag Name Description 0x01 FILE
Page 87 and 88: Figure 4-3: Sampling timing example
Page 89 and 90: We also mentioned before that there
Page 91 and 92: Code Instruction Description 0xA0 R
Page 93 and 94: Component Description 1 Indicates t
Page 95 and 96: last chapter. Figure 4-5: Automatic
Page 97 and 98: An important point to stress is tha
Page 99 and 100: (a) Rotation control (b) Zooming co
Page 101: 4.3 Communications Software The las
Page 105 and 106: Chapter 5 Analysis of Results and E
Page 107 and 108: Figure 5-1: Stress concentration po
Page 109 and 110: of the assembled skin patch don’t
Page 111 and 112: Node SG1 SG2 R(X) R(Y) Δ(X) Δ(Y)
Page 113 and 114: Or, ∆R = R3 R3 R3 + RC (5.2) Howe
Page 115 and 116: R3 Microstrain 162Ω −99.7337969
Page 117 and 118: Figure 5-3: Strain Gage electronic
Page 119 and 120: (a) Data from both strain gages (b)
Page 121 and 122: (a) Pressure data being extracted f
Page 123 and 124: many of these did not work as expec
Page 125 and 126: Data plots were also extracted for
Page 127 and 128: (a) Temperature sensor data plots (
Page 129 and 130: Figure 5-12: Raw microphone data wi
Page 131 and 132: (a) Activity sensor data (b) Whiske
Page 133 and 134: 5.3 Performance Metrics We have pre
Page 135 and 136: (a) I 2 C data when a 1500Ωs resi
Page 137 and 138: Component # per node Current consum
Page 139 and 140: Finally, since power is readily ava
Page 141 and 142: Chapter 6 Conclusions and Future Wo
Page 143 and 144: surface can be used to sense pressu
Page 145 and 146: Implement P2P Communications: curre
Page 147 and 148: Appendix A Abbreviations and Symbol
Page 149 and 150: Appendix B Bill of Materials 149
Page 151 and 152: Appendix C Schematics and PCB Layou
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1 1 2 2 3 3 4 4 D D C C B B A A Tit
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Amp1 P0Amp101 P0Amp102 P0Amp103 P0A
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P0Cin02 P0East06 P0North06 P0South0
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Cain P0C ain01 P0Cain02 L1 P0L101 P
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Figure C-10: Node Bottom Overlay 16
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4 3 2 1 A A Brain Communications Ac
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C3v P0C3v01 P0C3v02 Cavcc P0Cavcc01
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Appendix D Firmware 167
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C:\Documents and Settings\Gerardo\M
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Appendix E PC Code 183
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1 c:\Documents and Settings\Gerardo
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12 c:\Documents and Settings\Gerard
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Bibliography [1] John C. Ansel. Ski
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[33] Joseph Jacobson, B Comiskey, C
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[68] Vilis Tutis. The physiology of
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