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

jim jim at systemateka.com
Mon May 21 15:04:20 PDT 2012

```    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
> 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.
>         >
>         >
>         >
>         >
>         > 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
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>
>
>
>

```