# LED Strips Display driven from 555 / 4017 counter

Discussion in 'LEDs and Optoelectronics' started by mick1027, Dec 13, 2015.

1. ### mick1027

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Nov 26, 2015
Hi All,

I am expanding my knowledge from 555 timers to something that is more interesting to look at ( also to get my kids more interested ). I am looking at leveraging a 4017 counter using a 555. I would like this to drive a LED strip ( 12v 2A ). The strip is 300 LED but will most likely use less. From my research, I assume I should be looking at MOSFET transistor to do the higher voltage switching controlled from the high/lows of decade counter. correct. ?

I am planning on throwing together some diagrams soon but wanted to get some high level direction on the transistor.

Thanks,
Mick

2. ### duke37

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Jan 9, 2011
A 4093 (4 gates) or 40106 (6 gates) Schmitt nand gate can make a very simple oscillator with one resistor and one capacitor on each gate.
You need to know the voltage and current consumption of the LEDs before chosing the MOSFET.

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3. ### mick1027

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Nov 26, 2015
I see a few tutorial / explanations of Shmitt triggers out there. Do have a recommendation? this will be a new concept. thanks!

4. ### duke37

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Jan 9, 2011
If you can understand the 555 as an oscillator, then a Schmitt trigger oscillator will come as a pleasant surprise.
Put a resistor from output to input and a capacitor from input to ground. You will get an oscillator with equal on and off times, just the job for flashing LEDs. A 4093 gate has two inputs, these should be connected together.
The frequency f = 2.7/(RC) so 10μF and 270k will give 1Hz approximately.
Any unused gates should have their inputs connected to something, usually ground. The CMOS will supply very little current unlike the 555 but can drive a FET easily.

Using one output from a 4017 will give a 9:1 on of ratio but more than one output can be used.

I have the book 'CMOS Cook Book' by Don Lancaster (1977) but I do not know if it is still in print.

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5. ### mick1027

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Nov 26, 2015
I have been studying the 4093 and getting familiar with how it works. It is much easier than the 555. I do have a question though, what is the theory / concept on why unused gate inputs should be connected to ground if not used?

thanks

6. ### duke37

5,364
769
Jan 9, 2011
The inputs to CMOS have very high impedance so they will switch the gate from stray voltages in the vicinity. If the gate goes into fast oscillation, the gate will consume a lot of power and perhaps overheat.
Connecting the gate to something stops this wild behaviour.

If you use a 4093 gate driven from the oscillator, then you have two outputs to drive two LED strings, one being on when the other is off. The 40106 has six gates and could be used as an alternative to the 4093.
I often use the 4093 since I bought what I thought was one at a radio rally and I was handed a tube with well over a dozen in.

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7. ### AnalogKid

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Jun 10, 2015
I know the 4093. The 4093 is a friend of mine. The 4093 is one of the all-time great CMOS parts, and I routinely suggest it as an alternative to the 555.

BUT - the circuit described in post #4, with a single resistor and capacitor forming a symmetrical square wave oscillator, can be done with a 555. The advantages are that a 555 has significantly more accurate transition levels, so the oscillator accuracy is much better, and it does not drift with temperature changes. The disadvantage is that there are no extra gates left over to do other things. If *all* you need is one oscillator, the 555 gets you there with the same parts count in an IC package that is half the size of a logic gate.

ak

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8. ### GPG

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Sep 18, 2015
Second that

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9. ### mick1027

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Nov 26, 2015
Ok. I am moving along with this project getting closer to a design. I am using this LED strip start http://amzn.com/B00EKEODA0 . It can be cut @ every third LED. However, I am planning on using approx 75 to 100 LED strip.. I assume this would bring the total amps down from the 2 amps ( for the whole strip of 300 LEDs ). Two questions at this point.

1. should I be using a MOSFET which will switch the 12 volt rail for the lights
2. since I am using a 555 + 4017, should I use a voltage divider to bring this two a lessor voltage for the timing / counting circuit ( 6 volts ),. If so, should I use a voltage divider or regulator?

thanks !
Mick

10. ### AnalogKid

2,425
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Jun 10, 2015
The 555 and 4017 can run directly off the 12 V rail. Both chips can tolerate up to 18 V.

ak

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11. ### cjdelphi

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Oct 26, 2011
Ok, so you cut 10 strips for the 4017?

Each 4017 pin out will require a mosfet capable of delivering the max load, use a multimeter and get the total current (in series) used per strip..

This will tell you the minum load and the cheapest mosfets to do the job, if the total load is under 500ma... i might even consider a cheaper power transistor over a fet...

(Eg tip31/npn or similar)

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12. ### AnalogKid

2,425
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Jun 10, 2015
Not all TIP's are created equal. By datasheet, a 4017 will not saturate a TIP31 at Ic=500 mA. Real world parts, almost certainly. But there's not much margin for the base resistor value between undercurrenting the base and overcurrenting the 4017.

ak

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13. ### cjdelphi

1,096
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Oct 26, 2011
Depends on the current draw... i guess if you wanted to save extra, buy 50 2n2222s for a dollar or so, then use the 2n2222 and TIP31 in a darlington pair configuration....

That's providing you need the extra current, i'm sure in the real world a 200ohm resistor from the 4017 out to the base of the TIP31 should do what you want...

Infact, when it cools down (38c in the kitchen, 110f or so? I have my setup in there) i'll try it myself...

What's the max current for 4017? I'll google it lol

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Sep 18, 2015
15. ### mick1027

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Nov 26, 2015
Hi, thank you all for the feedback. I am learning a lot on the process of building my first real circuit. I really appreciate all the responses..

Here is my schematic--first version.

A couple of notes:

1. The LED strips, from what i understand can be connected directly to 12 volt source.
2. The LED strips have 3 LED per segment which are in series. For the schematic, I only show 2 segments. I am planning on having approx. 10 segments per each count for the first 3 and on the 4th count all segments will be light.
3. I have not gotten the full information on the LED strips yet. I will be getting that soon. I am not concerned with cost and do have several N type mosfets laying around from something else.. here is the type http://www.mouser.com/ds/2/200/irlb8721pbf-87377.pdf

16. ### mick1027

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Nov 26, 2015
Please take a quick look. I think I am close. I have done some prototyping with success. Did I miss anything?

File size:
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315
17. ### Colin Mitchell

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Aug 31, 2014
The LED strip is 99 cents on ebay !!!!!

Last edited: Jan 24, 2016