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# Chris20

Member Since: December 27, 2010

Country: United States

## Profile

### Spoken Languages

English, French

• The components I bought this year came (to me in Canada) from Canada, the States, Mexico, Israel, Myanmar, Malaysia, Japan, China, Taiwan, the UK, France, and India.
The cost of this “big world hug” is all the fuel spent transporting the stuff. Of course, it’s a bit difficult to get only components made in North America, nevermind just Canada.

• I believe the correct term is “thermal conductivity”. The thermal conductivity of a part is measured in Watts per Kelvin. Adding a heat sink to a part provides a low-thermal-resistance path to a larger surface area of air, which allows more Watts of heat dissipation per Kelvin of temperature difference between the part and the surrounding air. If you know the thermal conductivity from your part to the air, you can even calculate the exact temperature it will heat up to!
For these purposes, the air is regarded as having nearly infinite heat capacity, just as the ground is regarded as a nearly infinite reservoir of charge.

• Here is a bit of relatively complicated math for those who are interested (well, it’s not that complicated, but I don’t have a pic of the equation handy so I had to write it 15th-century style, with words.):
There is also a generalized voltage divider equation.
For a bunch of resistors R1, R2, R3… collectively Rn, where n = 1, 2, 3….
with corresponding input voltages Vn, n = 1, 2, 3…
and Gn is the conductance (Gn = 1/Rn) of each resistor,
The divider voltage (Vx or Vout) at the centre of the star topology is:
Vx = (sum of all (Vn times the corresponding Gn)) divided by (sum of all Gn)
Please write this on paper using sigma notation, and it’ll make more sense.
This is useful for MOS biasing calculations. For BJTs, you must make sure the divider current is much larger than the current the transistor will draw!
And it works with complex impedances too.
The voltage divider equation in this article is a special case of the general one, where there are two resistors (R1 and R2), and V1 = Vin, V2 = zero, and Vx = Vout.

• I understand why you shouldn’t use one resistor with multiple parallel LEDs, i.e.:
—–\/\/\/-——->|—
-—->|—
But is there any reason not to use one resistor for several series LEDs for lighting purposes?
—\/\/\/-—>|—->|—->|—

• As far as I know, it doesn’t matter.

• I’ve been told to create the heat bridge by placing the solder wire against the lead and pad, then putting the iron through that solder wire as you touch the joint. You then move the wire around to the other side to actually make the joint.

• Use Low for soldering small things like resistors and transistors. At that wattage you may need to pause between components to let the tip warm up again, but that’s better than overheating a chip!
Use the 40W mode for soldering larger things. For example, some board-mount potentiometers and switches have large “pins” which are just there to hold the part to the PCB. You would also use this mode for tinning large wires, like maybe some 16 or 14 AWG speaker wire. (Smaller AWG numbers mean thicker wire.)

• How does the computer understand the MCU’s language? Do you have to write a driver?

• With diodes it would work fine, but you would lose some voltage in the diodes. Schottky diodes would be best.

• I think this article needs one correction. You measure power density in W/kg, and energy density in W*h/kg. They aren’t the same thing. Energy density is how much energy (volts * amp-hours) is stored, and power density is how fast that energy can be delivered (volts * amps) without the battery overheating and exploding.
On a related note, I think you should add a blerb about the series resistance of a battery (how the voltage drops when you draw lots of current).

No public wish lists :(

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