YaMoron
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Infrared Bird Box project resistors

Thu May 17, 2018 4:20 am

I am hoping to do the Infrared Bird Box Camera project ( https://projects.raspberrypi.org/en/pro ... d-bird-box), but am I unsure about which resistors to purchase. The instructions it lists them as, "Some 220 Ohm 1% Resistors" but does not give any details such as wattage. Could someone please advise me?

pcmanbob
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Re: Infrared Bird Box project resistors

Thu May 17, 2018 6:30 pm

Hi.

You probably don't even need 1% tolerance resistors

220 ohm 5% tolerance 1/4 watt will be just fine and is what I would use.
Remember we want information.......................no information no help
The use of crystal balls & mind reading is not supported

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Burngate
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Re: Infrared Bird Box project resistors

Fri May 18, 2018 9:11 am

I find it slightly annoying that on the "What you will need" page it says "some" resistors and "some" LEDs. How many is "some"? Two? Twenty? Four thousand eight hundred and twenty seven?

As for the resistors, they're being used to control the current through the LEDs. Almost certainly the LED won't die if you give it 10% extra, and won't be very much dimmer if you give it 10% less, so 1% resistors is over-kill, as pcmanbob suggests.
220Ω is one of those preferred values, so more easily obtained than, say 210Ω, so that's probably why it's suggested.

Power-wise, the voltage across the resistor will be in the region of 3½v (5v less the LED voltage) so the power dissipated will be about 56mW (3.5*3.5/220 W). So ¼W (250mW) will be fine, or you could use ⅛W ones
However, I've found in the past that the leads on smaller-power resistors won't fit snuggly into those female-female jumper leads, so don't go too small!

http://cpc.farnell.com/search?ost=220%c ... nce=220ohm
A pack of 100 5% ¼W from CPC will cost you 57p. 1% ones are 72p for 50 - almost three times the price! Don't waste your money!

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bensimmo
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Re: Infrared Bird Box project resistors

Fri May 18, 2018 11:28 am

There is a good reason 220 is suggested an commonly used, but that's historical and efficient*

Anyway, at the bottom and end of each project there is a feedback option, do feedback so they know any troubles or questions.


*EDIT, just remembered an article in HackSpace Mag
https://hackspace.raspberrypi.org/featu ... lues-we-do

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Burngate
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Re: Infrared Bird Box project resistors

Fri May 18, 2018 5:48 pm

Nice article. Thanks, bensimmo.

Odd musings ...
... In the good old days, when electronics glowed, the valve filaments, at least the E ones such as ECC83, were 6.3v, which isn't in any E-series (P valves had their filaments in series and needed a current of 300mA, also not in any E-series below E24), so why was that value chosen?
Car batteries at 12v appear in the E12 series, but that's due more to chemistry than design.
Then TTL logic came along, using 5v, which also doesn't appear anywhere. So why that value?

And was our well-loved 3v3 chosen so as to appear in E6?
How about 1.8v and 1.2v?

I did say I was odd.

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