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

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8. Teardrops and filleting were added to all pads and vias. 9. Components were also chosen to be as small as possible, so that bend radius is not limited by this. If components are large, then the substrate will not be able to bend without components breaking off. There is one last thing to mention. Because of the necessary number of layers and the presence of surface mount components on both layers of the board, the nodes will certainly not be as flexible as a natural skin, plus are not, of course, elastic and 3-axis conformable. These and other results will be mentioned in Chapter 5. 3.3.2 Power Circuitry As we mentioned in the previous subsection, component selection was made in such a way so that component size and orientation would not much hinder the bending of the circuit. In general, this means selecting components as small and compact (not elongated) as possible, otherwise there would be a risk of components breaking off the substrate as shown in Figure 3-11(b). Referring back to the design principles of section 3.1, one of the key points is to have a reliable network. Reliability in the case of network power distribution is gained by providing each node with their own power supply or individually wiring each node to a centralized one. Connecting each node to a central power supply would be a step back in the design, because it would mean that each node has to be wired, which is exactly what we are trying to avoid by having processing power in each node. The other option would be to have a coin-cell battery in every node, but these are generally not rechargeable, bulky in relationship to node size and would hinder flexing motion. The next best option is to provide as many redundant power and ground connections throughout the network as possible. This is the option implemented in the SNAKE project, and therefore every node has a power and ground connection to each one of their immediate neighbors (North, South, East, West). Since the <strong>Skin</strong> Network topology is dictated by the 54
shape in which the nodes are connected, the nodes at the edges of whatever network shape is chosen would obviously have less than the four maximum redundant power links. The worst case scenario here, would be when the network topology is a straight link of nodes connected in a line, which provides no redundancy. Power to the network is therefore dis- tributed from a centralized unit, but no individual wiring is necessary, because each node provides power its adjacent neighbors. Each node is provided with a NCP553SQ33T1 linear voltage regulator that provides a constant 3.3V supply to each node. This regulator is ideal because not only does it come in a ultra-small and compact SC-70-4 package, but it also does not need any external components except for an optional output capacitor. It is an ideal regulator, because it has a 12V maximum input voltage, which allows for a very wide range of power supply voltages; it has an output current capacity of up to 180mA with a 650mV dropout, more than enough for the node circuitry, and it only consumes 2.8µA of quiescent power, which which suits our goal of low power consumption. Power requirements of the network vary widely, mainly because the size of the <strong>Skin</strong> will change, depending on the number of nodes connected. Either a large battery or a bench- top power supply can be used, but for the specific case of the skin patch built to test the project, a Rose Electronics LI-2S1P-2200 7.4V Lithium-ion battery pack was chosen, mainly because they were available from previous projects but also because they have a high-discharge rate of 2.20A/h. This means that if each node consumes an average of 15mA, one battery can provide enough power to operate roughly 140 Nodes for about an hour. Actual power consumption is much less than 15mA, but this and other results will be mentioned in Chapter 5. Figure 3-12 shows the power components. 3.3.3 Processor Microcontroller selection was also a critical part in the design of the Node Hardware. Fol- lowing with the established design principles, the chosen microcontroller should be capable 55
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Author S.N.A.K.E.: A Dynamically Re
Page 5: S.N.A.K.E.: A Dynamically Reconfigu
Page 9 and 10: Table of Contents Abstract 3 Acknow
Page 11 and 12: List of Figures 2-1 Created by MIT
Page 13: E-1 OpenGL Control Header File . .
Page 17 and 18: Chapter 1 Introduction “Imaginati
Page 19 and 20: The current project, named S.N.A.K.
Page 21: Hardware Each Skin Patch is compose
Page 24 and 25: living tissue. Particularly in the
Page 26 and 27: Figure 2-2: Leonardo’s Hand great
Page 28 and 29: Artificial Sensate Skins elsewhere
Page 30 and 31: 2.1.2 Ultra-dense Sensor Arrays Thi
Page 32 and 33: 2.2 Flexible Circuits Although, not
Page 34 and 35: 2.2.2 Other Technologies Figure 2-6
Page 36 and 37: human skin. The following design pr
Page 38 and 39: (a) Skin Patches as data extraction
Page 40 and 41: Figure 3-3: I 2 C Routing pattern T
Page 42 and 43: 3.2.2 Peer to Peer As we already me
Page 44 and 45: 5. Audio: by adding a MEMS micropho
Page 46 and 47: Table 3.1: Material thicknesses and
Page 48 and 49: (a) Node Front (b) Node Back Figure
Page 50 and 51: Figure 3-9: Skin Patch mechanical t
Page 52 and 53: used, which only further complicate
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 and 102: 4.3 Communications Software The las
Page 103 and 104: 4.3.2 Peer to Peer Peer to peer com
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Chapter 5 Analysis of Results and E
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Figure 5-1: Stress concentration po
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of the assembled skin patch don’t
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Node SG1 SG2 R(X) R(Y) Δ(X) Δ(Y)
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Or, ∆R = R3 R3 R3 + RC (5.2) Howe
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R3 Microstrain 162Ω −99.7337969
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Figure 5-3: Strain Gage electronic
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(a) Data from both strain gages (b)
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(a) Pressure data being extracted f
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many of these did not work as expec
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Data plots were also extracted for
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(a) Temperature sensor data plots (
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Figure 5-12: Raw microphone data wi
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(a) Activity sensor data (b) Whiske
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5.3 Performance Metrics We have pre
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(a) I 2 C data when a 1500Ωs resi
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Component # per node Current consum
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Finally, since power is readily ava
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Chapter 6 Conclusions and Future Wo
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surface can be used to sense pressu
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Implement P2P Communications: curre
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Appendix A Abbreviations and Symbol
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Appendix B Bill of Materials 149
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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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