NerdKits - electronics education for a digital generation

You are not logged in. [log in]

NEW: Learning electronics? Ask your questions on the new Electronics Questions & Answers site hosted by CircuitLab.

Support Forum » kit part list

November 10, 2009
by Michael
Michael's Avatar

I've enjoyed working through the NerdKits Guide pdf and getting my temp sensor up and running. Now I'm looking at the handful of other components which I'll be looking for inspiration to use.

Did I overlook an obvious parts list for my kit? P.20 in the pdf describes those needed for the temp sensor, but the others aren't mentioned. For example, I see my LEDs, and I know what color they are and which end is the anode, but I don't know what current rating they have. For that matter, I don't know what specs exactly define an LED. I've gathered from a forum post that this little 3-terminal blue thing is a potentiometer? I can't read the capacitance values on my capacitors, do I just need a magnifying glass? Or is it also listed somewhere?

November 10, 2009
by hevans
(NerdKits Staff)

hevans's Avatar

Hi Michael,

Glad you have enjoyed the NerdKit so far. There is currently not a comprehensive parts list included in the kit. It is definitely something we will consider doing. But if you have any questions about any of the parts, don't hesitate to ask here or vie email.

You are right, the blue guy with 3 terminals is a potentiometer. This is actually a remnant of an old version of our kit that used a potentiometer to vary the contrast on the LCD. We still include it just because they can be useful to have around, but it is not necessary for any of the projects in the guide.

The LEDs are 2.5V forwards voltage drop LEDs with a 30mA max current, although I would not recommend running them at more than 20mA. Below are links to the datasheets for the individual LEDs.

November 10, 2009
by mikedoug
mikedoug's Avatar

Humberto,

Can you link those in the members area with the rest of the datasheets? That way we don't have to search for them if we want to refer back at a later date!

Thanks!

MikeDoug

November 10, 2009
by mikedoug
mikedoug's Avatar

Here's what I see in the data sheets:

Red: 2.0V @ 20mA typical, 2.6V max; 30mA MAX
Green: 2.2V typical drop, 2.6V max, 25mA max (steady current) -- unclear
Yellow: 2.1V @ 20mA typical, 2.5V max; 30mA MAX

So if I were calculating, I would use:

    Red: 2.0V @ 20mA
  Green: 2.2V @ 25mA
 Yellow: 2.1V @ 20mA

Humberto, tell me where I'm going wrong -- because you state 2.5V -- but 'typical' sounds more like what you should engineer for. If the voltage drop is higher across the LED, then you'll get less current -- but if the voltage drop is LOWER than what you calculated for you will get MORE current and potentially enter into LED burn-out zones...

Correct?

MikeDoug

November 11, 2009
by hevans
(NerdKits Staff)

hevans's Avatar

You are right, I mistyped earlier. You should be designing for the "typical" voltage drop you would be expecting out of the LED, for these LEDs 2.1V is what you want.

If you want to be more correct you can look at the Forward Current vs Forward Voltage Drop graph. Then when thinking about what brightness you want, pick a current you want to run the LED at. Lets say I pick 10mA. Looking that graph (on the yellow LED datasheet) you would see that happens at about 1.95V. Quickly however, you realize that for most useful operating currents the voltage drop is about 2V, and you can just use that.

Summary: Sorry about the confusion. Use 2V as the LED forward voltage drop.

August 27, 2011
by bretm
bretm's Avatar

The datasheet for the green LED went away. Can we get these added to the download area?

Post a Reply

Please log in to post a reply.

Did you know that one NerdKits customer discovered that his hamster ran several miles in a night using his kit and a Hall-effect sensor? Learn more...