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| | | #REDIRECT [[Improving Phidgets Hardware Reliability]] |
| ==Introduction==
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| This primer will help you power your Phidgets while being safe to the electronics.
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| Basics
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| * Your circuit is a collection of garden hoses
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| ** Voltage is pressure
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| ** Amperage is the amount of water
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| * Interference can be created and absorbed by your circuit, both are undesirable
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| ** This interference is EM energy that travels through the air
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| ** It is especially produced by sudden changes
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| *** Even common things do this such as plugging in a long extension cord with nothing on the other end
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| **** The cord must equalize its electron balance with the wall power
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| **** The electron flow that makes this happen creates EM waves that affect (and potentially disrupt) electronics in the area
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| Picking a power supply
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| * Over-voltage rating matters, this will probably kill your circuit
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| ** Similar to putting so much pressure within a garden hose it blows up
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| * Over-amperage does not matter, the circuit can already control this
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| ** Similar to using a smaller nozzle on a garden hose - less flow
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| * Under voltage or under amperage and your circuit will:
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| ** Just not turn on
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| ** Turn on and then realize demands are too high, then turn off
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| ** Turn on and off, trying to fill the demands and then protecting itself for a short time before trying again
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| * Power supplies (even AC) have a set voltage, but that voltage is relative.
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| ** When a connection is first made, the board and supply settle their relative voltages.
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| ** This can generate a spark and feedback loop within the board
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| *** The board will get hot and should be unplugged within the first few seconds to prevent permanent damage
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| *** How to prevent?
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| Shielding
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| * Hard to do right
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| * Emissions hit shield and travel back to ground with resonance
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| Cables
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| * USB cables should be thick, and to spec
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| * USB depends on the fluctuations going out on +5V and back on ground to be well matched in time and distance
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| ** Their nearness causes their emissions to cancel each other out
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| ** Some cables have ferrite beads, which are low-pass filters (low frequencies pass)
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| *** This helps prevent a situation called USB common mode, where
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| * Some voltage is lost along the USB cable
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| ** Thin cables are more susceptible to this loss because they have higher resistance
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| ** The loss happens both ways, so the Phidget is running on a slightly reduced voltage gap from 5V
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| ** The thinner the cable, the more likely the Phidget will drop below its 4.5-4.6 V reset point
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| Size of circuit
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| * Circuits are always loops, and loops will resonate like antennas at a frequency determined by their size
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| * The smaller the loop, the higher the frequency
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| * Higher frequencies have a smaller potential to interfere with circuit frequencies
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| **Keep hookup wires short
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| Multiple power sources
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| * USB is one source, wall and battery power is another
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| * With only one device, not really a problem
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| * With more than one device, you create a closed loop between the two devices and the power source
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| ** Electrons can return via the grounds connecting both devices and the PC motherboard rather than just straight to wall or battery ground
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| ** Solutions:
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| *** Make the connections between all devices and battery or wall really desirable to electrons
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| **** Low resistance
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| **** Big fat wire
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| **** As short a wire as possible
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| ***Use a USB isolator
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| ***Use Ethernet for data rather than USB (or wireless), only for future Phidgets
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| * SBC complicates things...(three phidgets)
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