We started with 20 LEDs now we are up to 60? Where was it suggested to run a single LED from 12 V? From post 11 average current should be about 40 mA .

Hey thanks.. I don't know what it is about today but I replied early this morning and my replies are not here.. the schematic pretty much as [panic mode] said for 4017 driving leds via a transistor.. so I think the only question is how many leds can a BC548 drive at one time.. If the leds are from a 1 M white led light strip (60 leds) with smallest seperable group being 3 and total draws about 1 amp at 12V so to drive 6 should only draw 100 mA.. which I am told is ok for a BC548.

The project objective is a line of reasonably bright white LED's do some eye catching flash patterns or chases around the edge of a grad mortar board hat. Ok that said I wanted at least 10 LED's on each side. I bought a LED light chaser kit (555 -> 4017 -> 10KR ->BC548 -> 2 //leds <- 330R <- 12V bus) = 20 in total arranged interleaved as 2-10 right and 11-20 left.. but it only had red leds of low brightness. So my best buy was a 1 meter LED Light strip with 60 led's. But then I found I could not separate individual leds (easily in the time), they are grouped in 3's. So I thought if one BC548 could drive two groups of 3 white LEDs (6 total in parallel), I could use the whole 60 in two strips of 30 and get 15 per side with two chaser patterns, left half and right half.. all running from the 4017.

My battery is a DM 12 - 1.3 and I see 1.3AH on the side.. so at 100 mA I should expect to get 13 hours yes..

 

cmon, just use 4017 decade counter /decoder, clock it whatever you want (555), for each output connect two LEDs. in fact you can connect more than 2 LEDs if supply voltage is high enough...
http://www.allaboutcircuits.com/vol_6/chpt_7/6.html

Thanks.. yea I read that article.. its all good stuff here.. just a question of how many and for how long.

 

But you don't need a scanner for a schematic of the circuitry being used to drive the LEDs. Or take a picture with a smart phone and attach it. Multiple pictures if necessary.

Thank you.. I am sure I now have the solution I am seeking.. the 6 led's are just two groups from a led light strip... because they are stuck together to use the strip of led's how i want to I need to drive 2 groups of 3 from a single BC548.. x 10 times from the 4017. The LED bus voltage is 12V. Thanks again.

 

Anyone like to check my #12 question?

 

cmon, just use 4017 decade counter /decoder, clock it whatever you want (555), for each output connect two LEDs. in fact you can connect more than 2 LEDs if supply voltage is high enough...
http://www.allaboutcircuits.com/vol_6/chpt_7/6.html

Over 30 years ago, I bought a kit similar as that circuit, and they arrange the leds to be a circle, so we can play a guessing game to guess that which leds will be lighting when the time is up.

 

Over 30 years ago, I bought a kit similar as that circuit, and they arrange the leds to be a circle, so we can play a guessing game to guess that which leds will be lighting when the time is up.

Yea.. I am actually doing this thing for young school kids Christmas event.. I am the MC so I just want to jazz myself up a bit.

 

Your plan seems feasable. 10 strips on each side = 20 strips or 60 LEDs. Only 2 strips on at a time, 20 mA / strip = 40 mA, which is also average current. Battery , 12V @ 1200 mA h @ 40 mA drain = 30 hours. Normal base resistor closer to 2.7K rather than 10K, but I do not think that the difference would be noticed.
#12, 3 X 3.2V LEDs = 9.6V X .o2 mA = 192 mW; 12 X .o2 mA = 240 mW, so strip efficiency about 80 %.

 

Bernard, where did you get the 40ma average draw? The TS and I calculate 100ma. This would effect the battery life. 6 LEDs out of 60 is 10%. 10% of 1 amp is 100ma. Where'd we go wrong?

 

Your plan seems feasable. 10 strips on each side = 20 strips or 60 LEDs. Only 2 strips on at a time, 20 mA / strip = 40 mA, which is also average current. Battery , 12V @ 1200 mA h @ 40 mA drain = 30 hours. Normal base resistor closer to 2.7K rather than 10K, but I do not think that the difference would be noticed.
#12, 3 X 3.2V LEDs = 9.6V X .o2 mA = 192 mW; 12 X .o2 mA = 240 mW, so strip efficiency about 80 %.

Are you assuming the 3 LED's are in series.. I think they are in parrallel (I actually don't know for sure but there is one resistor for each diode on the strip of 3) so if the LED V drop is 3.2 V. Assuming the surface mount resistors connect each LED to the 12V bus. If the R is dropping (12 - 3.2 = 8.8V) then even though I don't know the current or R value my power comparison just becomes 3.2/12 = 26.6% power used and 73% waste..?

 

There is a lot of assuming going on, time to measure current of one strip of 3 LEDs operating on 12 V.

 

I found a sourse ( sinonled ) for parallel connected LEDs, 60 LEDs / meter that operate on 5 V.

 

There is a lot of assuming going on, time to measure current of one strip of 3 LEDs operating on 12 V.

Your right.. just doing it.. I connect my DVM on V-DC, I get 12.9V from the battery.. I connect the battery to the LED strip and all three light up fine.. then I set the DVM to mA, lead plugged in to mA socket, connect the battery and get nothing..!! just 000 on the DVM. I think I am missing something.. I try to measure the resistance value accros the terminals of the LED strip both ways and I get 000.. but maybe that's ok? So just as a check I connect the DVM in mA mode in series to one of the 10K resistors and get a reading of 0.37 mA.. which seems a bit strange.. should be 1.3 mA.? The R measures 10.01 K. No I don't have an oscilloscope and cannot check both V and A at the same time.

 

The GND(earth link) is the common pin, so you can cut if off, the only thing you can do is cut the 12V pin.

Unless you separate them to 10 different pieces.

You are correct.. I discovered I can leave the earth common and split them at the 12V bus but only in groups of 3.