# Do-it-yourself Chanukiah (with LEDs?) **URL:** \ **Category:** Factual Questions\ **Created:** [December 19, 2005, 7:19pm UTC](https://boards.straightdope.com/t/do-it-yourself-chanukiah-with-leds/336330 "2005-12-19T19:19:12Z")\ **Posts on this page:** 4\ **Page:** 2
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [December 20, 2005, 1:28am UTC](https://boards.straightdope.com/t/do-it-yourself-chanukiah-with-leds/336330/21 "2005-12-20T01:28:22Z")
Oh, you want a switch on LED? Well that changes things a bit! > [@Q.E.D.](#): > > If you wish to able to control the LEDs individually, you’ll need to use something like **bouv** ’s schematic. In series with each LED, you’ll need a current-limiting resistor of the proper value. To determine the proper resistance, you’ll need to know the forward voltage drop across the LED (typically about 1.8-2 volts for gallium-arsenide red or green LEDs) and the driving current. The maximum forward current will be listed on the LED package, and is typically around 20 mA. Drop it down a few mA for safety, say, around 10 mA. To calculate the resistor, subtract the forward voltage drop from the supply voltage and divide the result by the driving current. For example, if you are using a 9 V batter, and you have a red LED with a forward voltage drop of 2 V to be driven at 15 mA, you’ll need a resistor of (9 - 2) / .015 or 466.6 ohms. The closest standard value would be 480 ohms, so use that. Yea, that will work. But as mentioned, I still prefer the LEDs to be in series (for a number of reasons). And using a constant current source is the way to go. If he wants each LED to be individually controllable, then use the LM317 & LED series arrangement (described above) and add a switch in parallel with each LED. When the switch is closed the LED will turn off. And no, it won’t hurt the constant current source to have all the switches closed. ---
**Author:** ![Kyla](https://avatars.discourse-cdn.com/v4/letter/k/eada6e/32.png) [@Kyla](https://boards.straightdope.com/u/Kyla)\ **Post date:** [December 20, 2005, 1:49am UTC](https://boards.straightdope.com/t/do-it-yourself-chanukiah-with-leds/336330/22 "2005-12-20T01:49:44Z")
> [@633squadron](#): > > BTW, the exact transliteration is **chanukah**. Tons of confusion here. Wikipedia gives a ton of alternatives. Not sure why. The Hebrew is [SIZE=3]חנכה[/SIZE} which would be ch-n-k-h (hebrew having no values traditionally). :dubious: I disagree; there are no “rules” on how to transliterate Hebrew into Latin characters. If you can get the meaning across, you’re transliterating it correctly. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [December 20, 2005, 1:51am UTC](https://boards.straightdope.com/t/do-it-yourself-chanukiah-with-leds/336330/23 "2005-12-20T01:51:26Z")
If you really want to get fancy, you can use something like a 4017 decade counter, set to recycle at 8. Wire a momentary switch between Vcc and the Clock In terminal, and you can turn each LED on in turn until they are all lit. ---
**Author:** ![633squadron](https://avatars.discourse-cdn.com/v4/letter/6/ee59a6/32.png) [@633squadron](https://boards.straightdope.com/u/633squadron)\ **Post date:** [December 20, 2005, 2:14am UTC](https://boards.straightdope.com/t/do-it-yourself-chanukiah-with-leds/336330/24 "2005-12-20T02:14:57Z")
> [@Q.E.D.](#): > > If you really want to get fancy, you can use something like a 4017 decade counter, set to recycle at 8. Wire a momentary switch between Vcc and the Clock In terminal, and you can turn each LED on in turn until they are all lit. Yeah, but I’m gonna leave that for next year. I’ll be lucky to get _anything_ working for this year! While it’s true that there aren’t any “official” rules for transliteration, writing it as hanukah when it starts with a “chet” is misleading. Yeah, yeah, this is a nit. So sue me! I’m just a bit sensitive to having my cultural heritage diluted by the vast sea of Western European Christianity. [Previous page](https://boards.straightdope.com/t/do-it-yourself-chanukiah-with-leds/336330.md?page=1)