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.

Project Help and Ideas » led swap

December 03, 2010
by igondjo32
igondjo32's Avatar

Technical SpecificationsLite-On LTL-307EForward Voltage 2.00 V i was supply few LEDs with my leds array kit can i swap them with those i am discribing bellow ? if yes what resistor would i use the 10k or else thanks

Luminous Intensity 19.0 mcd Size-Diameter 5.00 mm Size-Height 8.60 mm Wavelength 635 nm Operating Temperature 100 °C (max)
Color Red Lead-Free Status Lead Free Lens Type Diffused Packaging Bag RoHS Compliant

December 03, 2010
by BobaMosfet
BobaMosfet's Avatar


Use a voltmeter with a diode function and connect one of your 635nm, 5mm LEDs to the meter. If the LED fails to light and it reads about zero, reverse the connection and see if it lights. If it does, the meter should tell you what voltage is required to fire the LED.

Beyond that, simply limit the amount of current through the LED (I usually don't allow more than about 20mA (That's 2 hundredths of an Amp, or 20 thousandths).

So, if your nerdkit's LM7805 provides about 5V, and the LED requires about 1.76V (typical), then you calculate your resistor size (to limit the current through the LED) this way:

R = E / I
R = (Supply Voltage - LED Firing Voltage) / .020 Amps
R = (5 - 1.76) / .020
R = 3.24 / .020
R = 162 Ohms.

Since there is not a 162 Ohm Resistor, and we don't want to exceed the 20mA, we'll use a 170 Ohm Resistor (resists more current). 170 Ohms is Brown Violet Brown. 4th band can be gold. This is if you're using carbon-film resistors (normally what you have).

See-- you can figure this out for any LEDs you have.


April 20, 2012
by RogerFL
RogerFL's Avatar

The library article that refers to this thread has a minor error in it. This page:

This sentence:

180 ohms is Black-Gray-Brown.

I think should read:

180 ohms is Brown-Gray-Brown.


April 20, 2012
by Ralphxyz
Ralphxyz's Avatar

Hi RogerFL, you are correct. Now the great thing about the Nerdkit Community Library is that it is WiKi based meaning the "community" is responsible for accuracy.

So this gives you a excellent chance to learn how to edit a Library page.

Become a registered user and then just click on "edit this page" in the lower right corner.

This error is a great illustration for anyone especially, a new inexperienced person, to not be intimidated about posting to the library for fear of making mistakes. bretm, the original posted is/was one of the most highly skilled programmers here in the Nerdkit forum but even he can make a mistake an anyone from the community can and should make corrections.

Perfect example, go for it, and thank you for pointing this out!


Post a Reply

Please log in to post a reply.

Did you know that you can connect a pushbutton to a microcontroller with only one wire? Learn more...