Electricity Primer: Difference between revisions
From Phidgets Support
No edit summary |
|||
Line 13: | Line 13: | ||
** It is especially produced by sudden changes | ** It is especially produced by sudden changes | ||
*** Even common things do this such as plugging in a long extension cord with nothing on the other end | *** Even common things do this such as plugging in a long extension cord with nothing on the other end | ||
**** The cord must equalize its electron balance with the wall | **** The cord must equalize its electron balance with the wall power | ||
**** The electron flow that makes this happen | **** The electron flow that makes this happen creates EM waves that affect (and potentially disrupt) electronics in the area | ||
Picking a power supply | Picking a power supply | ||
Line 34: | Line 34: | ||
* Hard to do right | * Hard to do right | ||
* Emissions hit shield and travel back to ground with resonance | * Emissions hit shield and travel back to ground with resonance | ||
Cables | |||
* USB cables should be thick, and to spec | |||
* USB depends on the fluctuations going out on +5V and back on ground to be well matched in time and distance | |||
** Their nearness causes their emissions to cancel each other out | |||
* Some cables have ferrite beads, which are low-pass filters (low frequencies pass) | |||
* Some voltage is lost along the USB cable | |||
** Thin cables are more susceptible to this loss because they have higher resistance | |||
** The loss happens both ways, so the Phidget is running on a slightly reduced voltage gap from 5V | |||
** The thinner the cable, the more likely the Phidget will drop below its 4.5-4.6 V reset point | |||
Size of circuit | Size of circuit |
Revision as of 18:24, 12 January 2012
Introduction
This primer will help you power your Phidgets while being safe to the electronics.
Basics
- Your circuit is a collection of garden hoses
- Voltage is pressure
- Amperage is the amount of water
- Interference can be created and absorbed by your circuit, both are undesirable
- This interference is EM energy that travels through the air
- It is especially produced by sudden changes
- Even common things do this such as plugging in a long extension cord with nothing on the other end
- The cord must equalize its electron balance with the wall power
- The electron flow that makes this happen creates EM waves that affect (and potentially disrupt) electronics in the area
- Even common things do this such as plugging in a long extension cord with nothing on the other end
Picking a power supply
- Over-voltage rating matters, this will probably kill your circuit
- Similar to putting so much pressure within a garden hose it blows up
- Over-amperage does not matter, the circuit can already control this
- Similar to using a smaller nozzle on a garden hose - less flow
- Under voltage or under amperage and your circuit will:
- Just not turn on
- Turn on and then realize demands are too high, then turn off
- Turn on and off, trying to fill the demands and then protecting itself for a short time before trying again
- Power supplies (even AC) have a set voltage, but that voltage is relative.
- When a connection is first made, the board and supply settle their relative voltages.
- This can generate a spark and feedback loop within the board
- The board will get hot and should be unplugged within the first few seconds to prevent permanent damage
- How to prevent?
Shielding
- Hard to do right
- Emissions hit shield and travel back to ground with resonance
Cables
- USB cables should be thick, and to spec
- USB depends on the fluctuations going out on +5V and back on ground to be well matched in time and distance
- Their nearness causes their emissions to cancel each other out
- Some cables have ferrite beads, which are low-pass filters (low frequencies pass)
- Some voltage is lost along the USB cable
- Thin cables are more susceptible to this loss because they have higher resistance
- The loss happens both ways, so the Phidget is running on a slightly reduced voltage gap from 5V
- The thinner the cable, the more likely the Phidget will drop below its 4.5-4.6 V reset point
Size of circuit
- Circuits are always loops, and loops will resonate like antennas at a frequency determined by their size
- The smaller the loop, the higher the frequency
- Higher frequencies have a smaller potential to interfere with circuit frequencies
- Keep hookup wires short
Multiple power sources
- USB is one source, wall and battery power is another
- With only one device, not really a problem
- With more than one device, you create a closed loop between the two devices and the power source
- Electrons can return via the grounds connecting both devices and the PC motherboard rather than just straight to wall or battery ground
- Solutions:
- Make the connections between all devices and battery or wall really desirable to electrons
- Low resistance
- Big fat wire
- As short a wire as possible
- Use a USB isolator
- Use Ethernet for data rather than USB (or wireless), only for future Phidgets
- Make the connections between all devices and battery or wall really desirable to electrons
- SBC complicates things...(three phidgets)