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0 pointslondons_explore1y ago0 comments

Being a mostly-digital electronics guy, I think 0.1, 1, 10, 100, 1k, 10k, 100k, 1M and 10M is a perfectly fine series for pretty much any usecase.

Sense resistor? 0.1 ohm.

Resistor for an LED: 100 ohm

Pull up resistor: 10k

Bias resistor for some mosfet gate: 10M

Voltage divider to measure the battery voltage with an ADC: two 100k resistors.

It's super rare I need anything else. I hate fiddling about with switching the reels on the pick'n'place anyway.

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picture1y ago

Have you tried 10 kΩ for LED and FET pull down?

100 Ω sounds like way too much current for modern LEDs. I often end up using 100 kΩ especially for green LEDs. They are very visible under indoor lighting even with 1 MΩ and 3.3 V supply.

For pulling down FETs, you want something in the range of 10 kΩ. 10 MΩ sounds way too high, which makes your circuit sensitive to being touched or affected by moisture, especially if there are near by components connected to the power rail.

My digital electronics grab bag consist of 22 mΩ for sensing, 100 kΩ for battery voltage divider, 22 kΩ for one of the 3.3 V buck converter feedback dividers, 10 kΩ for everything else like I2C pulling.

hathawsh1y ago

Are you sure all those numbers are in the right ballpark? With a 3.3V supply and a 1 MΩ resistor, the most current you can get from that circuit is in the neighborhood of 3μA, and that's ignoring the LED voltage drop. I would think the LED won't be visible until you're around the mA range. Or are some LEDs visible in the low μA range?

tuetuopay1y ago

Modern LEDs light up with incredibly low currents. In a RF noisy environment, I've often seen LEDs glow just by touching one side with a wire and the other to ground. Just the parasitic from such a crude antenna was enough.

Of course as stated by another comment, our eyes are also incredible, and can pick up very faint amount of light.

londons_exploreOP1y ago

human eyes are logarithmic and can easily see microamps.

In fact, just hold an LED between your fingers in a dark enough room and you'll sometimes see them glow from stray magnetic fields inducing enough current in your body to light them.

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CamperBob21y ago

Resistor for an LED: 100 ohm

Yeah, that's why I can read a book by the blue LEDs on my alarm clock...

_carbyau_1y ago

https://www.3m.com/3M/en_US/p/d/b40068069/

Depending on the colour bleed though. It may wipe out all visibility of the clock numbers.

Liftyee1y ago

And to think a little dimming circuit with LDR/phototransistor (RoHS..) is practically electronics 101...

klodolph1y ago

I do mostly analog and being off by a factor of 2 or 3 is gonna ruin your day.

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