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

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(a) Skin Patches as data extraction devices (b) Skin Patch in stand-alone mode Figure 3-2: Skin Patch modes of operation PC with a brain in a data extraction scenario, or by themselves as a stand-alone sensing- processing-actuation distributed platform. The former may be useful to monitor pressure gradients on an airplane’s wing, when this is tested inside of a wind-tunnel for example. The later would be better suited if the material is to be used as an interactive architectural material 3 . Figure 3-2 shows the two ways the Skin Patch Network can work. We now describe the different communication links that the project contains. Although these links are designed according to the specific needs of the involved elements, many of the points described above are observed during the design of these communications channels. Reliability, for example, is a key issue because the integrity of the network depends on the stability of the communications links. For this reason, several redundant links are provided for the backbone network. Scalability is also observed and specific measures were taken to ensure this. We will come back to these points though when the links are individually described. 3.2.1 I2C Backbone According to the previous section, the Skin Patches are equipped with a network backbone. There are of course many ways of implementing it, but which is the adequate for the project? 3 More on this point is provided in the Actuation and Sound sensing sections 38
It is clear that a serial protocol must be used to avoid the high number of lines that a parallel port would require, but then again, which one is the right option? There are a multitude of serial protocols for embedded systems to choose from: SPI, I 2 C , Microwire, UART, RS-232 and others. To make the right choice, we have to start from what we know: The Skin Patch network can be made up of tens up to a few hundred nodes. One of the goals of the project is to minimize bandwidth through local processing of data. If the skin is working as a stand-alone device, it would be desirable to use the backbone as a multi-master, multi-slave bus. If the skin is connected to a computer, it would be desirable to have only one master (the Brain) and multiple slaves (the nodes), depending on whether multiple patches are needed Number of communications lines should be minimized to decrease wiring complexity. By taking this into consideration, we can easily discard SPI because it can’t be used as a multi-master bus and needs four lines plus a common ground; we can also discard UART, RS-232, and Microwire, because they can’t handle more than 2 devices without multiplexing. I 2 C on the other hand is capable of doing everything outlined above and it can be run at up to 400Kbps in fast mode and up to 3.4Mbps in high-speed mode. Moreover, the chosen microcontroller has an I 2 C hardware module so it does not even need to be implemented in software and it also requires only 2 lines: Serial Data (SDA) and Serial Clock (SCL). Running I 2 C at the higher speeds requires special considerations, however. The I 2 C bus can allow multiple devices to be connected connected to the data lines, because it uses what is referred to as a wired and, which means that the lines can be pulled down, but not up to avoid short circuits. This is accomplished by using either open collector devices or by alternating the states of the connected devices between high-impedance and a permanent pull-down. 39
Page 1: 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 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 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
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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
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We also mentioned before that there
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Code Instruction Description 0xA0 R
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Component Description 1 Indicates t
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last chapter. Figure 4-5: Automatic
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An important point to stress is tha
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(a) Rotation control (b) Zooming co
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4.3 Communications Software The las
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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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