Random Blink LEDs (Total 36w) Raise Amps Help Please!

Thread Starter

JKC111

Joined Jun 1, 2014
1
Hi everyone. My issue is my chip not supplying the amps I require.

I'm trying to make two 6w bulbs and a single 30w LED strip all blink/flash randomly (completely randomly, but I'll need to adjust the frequency of the change) independently, in the same style as a broken fluorescent tube that can't quite start.

This is the kind of effect I'm trying to achieve:
http://www.youtube.com/watch?v=OU9XZZdA_sA
(00:19-00:22)

Using this circuit:
http://rookieelectronics.com/sequential-random-led-flasher/

My issue is the chip (4026 counter and display driver) only supplies 100mA to each of the 8 channel, where as I need 2x 500mA and 1x 2A channel, all blinking independently. Perhaps there is a better way of doing what I am trying to achieve. Also, this is all held within a small wooden box unit (it's an art installation piece) so I'm worried about the size and heat dissipation of using multiple transformers, if that's what I should use.

Here are the diagrams for the circuit in which I need to raise the amps on 3 of the channels:




Here is a guy that's done it, but I don't understand the circuitry he's used (description under photo, scroll left/right for other photos)
http://s1006.photobucket.com/user/jwheat058/media/Fluorescent Light Prop/P8030317.jpg.html?sort=3&o=5

Thanks for all your help!
 
Last edited:

AnalogKid

Joined Aug 1, 2013
8,467
One big problem that leads to other issues. The 4026 does not have any internal current limiting other that the nature of CMOS transistors. The outputs are *not* designed to drive LEDs directly. The circuit you have works without the 4026 burning up because of device physics, not because of conservative circuit design. No way will it supply 100 mA.

The 4026 data sheet shows both emitter follower and common emitter segment driver examples. Since you are (correctly) concerned about heat, go with common emitter drivers, otherwise known as open collector switches. If size is an issue, you can use a small transistor like a 2N4401 for the 100 mA outputs and a TIP120 for the bigger ones. It should stay cool enough without a heatsink.

ak
 

#12

Joined Nov 30, 2010
18,210
You are going to have to add some current drivers. The slow speed and the high current needed in this design make this an ideal candidate for mosfets. Unfortunately, I don't know where to buy parts in London, so that's going to have to be the subject of another post in this thread.

Here's a drawing of how to arrange the parts.
 

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Bernard

Joined Aug 7, 2008
5,526
You can make fairly good random blinking with a LED tea light as source. I think Bill Marsden found a repeating pattern at about 300 bits. Use a seperate blinking LED for each channel with app. drivers.
What is power source?
 

AnalogKid

Joined Aug 1, 2013
8,467
Back to the original circuit, note that a) the LEDs do not all blink the same number of times in a 10-count cycle; b) sometimes there are more than 1 LED on at the same time, sometimes only 1; c) Sometimes an individual LED is on for 2 or three counts in a row, making it apppear brighter than the other ones.

If you want something more evenly weighted, change the 4026 to a 4017. Each LED comes on only once in every 10-count cycle, and only 1 LED is on at any given time. You can physically arrange the LEDs for a pseudo-random appearance.

ak
 

AnalogKid

Joined Aug 1, 2013
8,467
Yeah. I wouldn't use the Carry output. It is the only one that blinks steadily, and acts as a visual trigger to see the repeating pattern in the rest of the lights.

Another trick, this time for a decoded 7-segment display, is to pass BCD through a gray code converter. It is easier to see the repeating pattern emerge because people automatically look for patterns in numbers, but not in an unlabeled string of blinking dots.

ak
 
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