[Noisebridge-discuss] Shameless Frantisek Impersonation (Re: LED Calculations help)

Christoph Maier cm.hardware.software.elsewhere at gmail.com
Mon May 21 18:07:37 PDT 2012


As Miloh already mentioned, the 2-wire blinky LEDs are not just LEDs, but
an analog circuit with built-in current limiter;
probably something even better than a resistor.
I'd expect the LEDs to turn on and start blinking at some voltage, then
draw current that increases only very little,
and finally get fried and fail as you turn up the voltage. I would guess
that the LEDs can handle more than 5V.

Still greetings from Seoul, where I'm learining the concept of "love motel".

Christo^H^H^H^H^H^H^HFrantisek

On Tue, May 22, 2012 at 7:04 AM, jim <jim at systemateka.com> wrote:

>
>    Good advice! Thanks.
>    I believe that no LED works on less than
> 1.5+ volts (1.7VDC comes to mind), and generally
> LEDs turn on at about 5mA and get brighter as
> the current increases until they fry. I believe
> they fry open not shorted and that any LED ought
> to take at least 20mA without frying.
>    If the things are scarce, get a lab supply
> that measures both voltage and current and start
> with 1.5V and see what the current is and judge
> the brightness; raise the voltage until 10mA
> current flows and judge the brightness; raise
> current to 15mA and judge; go as high as 20mA
> current and hope that's bright enough. 25mA is
> in the risky area.
>    Note that each LED may have a distinct ratio
> of current to brightness; if so, that argues for
> a separate current limiting resistor for each
> LED (or for the outlying cases).
>
>
>
> On Tue, 2012-05-22 at 04:20 +0900, Christoph Maier wrote:
> > Another Frantisek Apfelbeck impersonator here, hailing from Seoul:
> >
> > For electrical purposes, these circuits are not LEDs, but integrated
> > two-terminal blinkylight integrated circuits.
> > As such, they have built-in current limiting and can be operated
> > directly off a battery.
> >
> > As they apparently don't have a datasheet that is 1. not in Chinese
> > and 2. available,
> > it might make sense to sacrifice one or two of the LEDs by hooking
> > them up to a laboratory power supply that displays both voltage and
> > current,
> > then to ramp up the voltage from 1.0V in small increments until the
> > LEDs get fried, while measuring current and observing brightness.
> >
> > If I recall correctly, Jimmie Rodgers gives away these blinky LEDs
> > with a battery [http://en.wikipedia.org/wiki/CR2032_battery] when he
> > gives basic soldering instruction.
> >
> > Greetings from Seoul,
> >
> > ... Frantisek?
> >
> > On Mon, May 21, 2012 at 11:48 PM, jim <jim at systemateka.com> wrote:
> >
> >
> >            What kind of LEDs? Different types have differing
> >         voltage drops and current ranges.
> >
> >
> >
> >         On Sun, 2012-05-20 at 22:16 -0700, Phil Spitler wrote:
> >         > Hi,
> >         > For simple LED projects, I usually use an online LED
> >         calculator to get
> >         > the values for the needed resistors.
> >         >
> >         >
> >         > I have just ordered some LEDs online but the specifications
> >         don't list
> >         > the forward voltage, just the current draw.
> >         >
> >         >
> >         > http://www.adafruit.com/products/679
> >         >
> >         >
> >         > How would I figure out how to power the LEDs and what
> >         resistors to
> >         > use?
> >         >
> >         >
> >         > I am thinking of using 10 LEDs and having them all powered,
> >         all the
> >         > time.
> >         >
> >         >
> >         > I would love to know how to calculate my needs.
> >         >
> >         >
> >         > Any ideas?
> >         >
> >         >
> >         > Cheers.
> >         >
> >         >
> >         > Phil
> >
> >
> >         > Phil Spitler |   Associate Creative Director  |  Bonfire
> >         Labs |  t :
> >         > 415.394.8200  |  c : 415.571.3139  |  Bonfirelabs.com
> >         _______________________________________________
> >         Noisebridge-discuss mailing list
> >         Noisebridge-discuss at lists.noisebridge.net
> >         https://www.noisebridge.net/mailman/listinfo/noisebridge-discuss
> >
> >
> >
> >
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.noisebridge.net/pipermail/noisebridge-discuss/attachments/20120522/001b6fe8/attachment.htm 


More information about the Noisebridge-discuss mailing list