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Topic: Is it safe to connect a #30 bulb directly to the arduino output pin (Read 1 time) previous topic - next topic

smeezekitty

Avoid throwing electronics out as you or someone else might need them for parts or use.
Solid state rectifiers are the only REAL rectifiers.
Resistors for LEDS!

CrossRoads

Maybe ... The specs seem to say it has 21mA current draw at 4.5V
I think I'd measure its 2 leads, see if it has reading of around 200 ohm to confirm that.
Or get a current measurement while powering from 3 AA batteries for confidence first.
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retrolefty

#2
Feb 23, 2011, 07:20 am Last Edit: Feb 23, 2011, 07:25 am by retrolefty Reason: 1
Quote
Is it safe to drive directly from a pin?


Well the spec sheet says:  4.5 Volt 0.021 Amp. So that would on the surface say it would work great with an Arduino output pin. However (seems there is almost always a however) incandescent lamps have a property that initially there cold resistance will be lower then it's running resistance. So what is it's inrush current, and would it exceed the Arduinos absolute 40ma limit. I don't know, do you? I guess you could measure it's cold resistance to see how bad a situation it might be, but that doesn't tell you how fast it's resistance increases from inital turn on.

I would rather ask, why use an incandescent lamp at $2.73 a pop, marked down from $3.25? High brightness white leds are cheaper (.32 each in bulk, link below) then that and have no current inrush problem, and don't burnout like incandescent lamps.

http://www.sparkfun.com/products/9850

Lefty

Magician

No, it's not safe.
In cold state resistance approx. 10 times less than it in hot condition.
It would overload output when turn on up to 200 mA, that is too much.


smeezekitty

The measured current draw at 4.8v input is 26ma.
Quote


I would rather ask, why use an incandescent lamp at $2.73 a pop, marked down from $3.25? High brightness white leds are cheaper then that and have no current inrush problem, and don't burnout like incandescent lamps.


A. I already have one
B. It casts omni directional light
C. It can be PWM'd without flickering.
Avoid throwing electronics out as you or someone else might need them for parts or use.
Solid state rectifiers are the only REAL rectifiers.
Resistors for LEDS!

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