"Classic" 6-digit Arduino Nixie Clock Revision 5 LED questions

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1 month 1 week ago #12248 by Dkivett
As i said in the title I have a Classic Rev5 with WIFI
I have the kit fully assembled and its working great. I am finishing up the case and LEDs
I was running some tests on the leds I was doing a test, i know that your supposed to use separate 1k resistors for each leds in series and that you can run 6 leds total. Well I have a bit of a space issue and having 3 resistors for each led seems bulky and I would really like more then 6 leds so I did some tests with 4 leds in parallel hooked to 1k resistors on the R G B cathode leads and on average they pulled about .93 ma DC the anode (tick) reads about 3.11 ma.
My test is running 4 leds with about 1.0 mA (rounded up) so max power in the instructions says 200mA so then couldn't I run about at least 20 Leds Safely? (i think 800 if my math is right (its probably not)) and i don't understand based upon my test they all the resistors should be in series the wattage to run ea. LED is miniscule(.002 watt) so if ea. 1k resistor was 1/4 watt. Is your safety margin just that? Knowing that each customer wont get identical parts and that some LEDS may vary did you leave a factor of 10x in your safety margin and of course my math/understanding may be off by a factor of 100x.
so Simply Put can i run 5 parallel Leds (to each group of 3 1k (.25 watt) resistors (1per cathode)) and run 2 groups of theses( total of 10LEDS) (I'll try to attach photos tomorrow)

I am not sure this is making any sense i do have a lot of supporting photos that i will attach tomorrow.

BTW i did try to use the search function but wasn't successful i know your rebuilding it now can you make it group each item by the author (with the ability to expand them)
all i found was several pages of the most recent led issue. i was surprised to find several hundred pages of RGB LED issues. I doubt this is a unique question, and I don't want to waste any time so if there is a simple yes or no that would be great or yes i can do 10 LEDS, no they cant be in parallel? a quick answer like that would be great too
and please explain it like I am a 12y/o I'm 40+ but I successfully never grew up (no theory and equations)

I just want to say thank you the kit is great, but more importantly
Thank you for having this community. I bought a kit from another guy that said i should have an electrical engineering degree to safely build the kit (then in the suggested tools he listed toe nail clippers to use as wire cutters) I am just glad that kit worked with not problems cuz i am sure there was no support
Again
Thank you all so much
Dave
(no smoking crater) so far

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1 month 1 week ago #12249 by Ty_Eeberfest
Moved your post to the Kit Support forum where it will get more attention.

I'm having a hard time following your explanation so I will wait for the pictures before I say much. I will say that LEDs running at only 1mA sounds strange. LEDs typically want to be run at 10 - 20mA. Yeah they will light up at 1mA (sometimes) but I can't imagine they would be very bright at all.

I'm laughing at the "need EE degree but use toenail clippers to cut wire" kit. Gotta love eBay.

Look into it later when the dust is clearing off the crater.

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1 month 1 week ago #12250 by Dkivett
I used my meter and put it in line with the cathodes the pic with the 0.92
the 3.12 are on the anode. I know i didnt explain my question that good but hopefully these photos will show how i have it set up

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1 month 1 week ago #12251 by Ty_Eeberfest
Okay, I still can't make any sense of those meter readings. I can only guess that maybe the fact those LEDs are driven with a PWM signal is confusing the meter. The readings are low - almost absurdly low.

Getting back to your original questions. The 2N7000 FETs can sink 200mA which would be 10 LEDs at a really bright 20mA each. 20 LEDs at a somewhat less bright 10mA each. The choice of resistors sets the current and thus the max number of LEDs.Take a look at the attached sketch. Is this what you are wanting to do - 10 LEDs with minimal resistors? The circuit in the sketch will do it but it's a really awful design. It will probably work but it's dodgy. The right way to do it is to use 3 resistors on each LED. When you start skimping on resistors you are relying on the LEDs to share the current evenly amongst themselves. That may or may not go well depending on LED manufacturing tolerances. (I dunno... the Chinese do it all the time on strings of battery operated LED Christmas lights... doesn't make it right though)

I think you asked about wattage too, If you go with this dodgy design the 1K resistors on the clock board will need to be changed to 100 ohm 1/4 watt and the 100 ohm resistors shown on my sketch should also be 1/4 watt.


Look into it later when the dust is clearing off the crater.
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1 month 1 week ago #12252 by Ty_Eeberfest
Forum insists on scaling my image down to where you can't read the text. Here is an unmolested version:

i.imgur.com/FkOmqH4.png

Look into it later when the dust is clearing off the crater.
The following user(s) said Thank You: Dkivett

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1 month 1 week ago #12253 by Dkivett
I am going to scrap the idea of cheating and do it the right way and have resistors for ea LED, I believe i can run 9 leds and still have a small margin of safety, would I still use 1K resistors or would i use a 680 ohm?
I really appreciate all the help
Thanks
Dave

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