Discussion in 'General Electronics Chat' started by abhimanyu143, Jun 2, 2015.

1. ### abhimanyu143 Thread Starter Member

Aug 25, 2014
211
1
Hello
how to blink led 10 times for 30 second without MCU ? Is this possible ? simply when we use MCU. we use registers and counter.
look my incomplete diagram . tell me how to create delay for 30 second

2. ### ErnieM AAC Fanatic!

Apr 24, 2011
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First let's think of a way to blink a LED continiously. If you want 10 times in 30 seconds a clock of 1/3 Hz will do this. A '555 can make close to a square wave so you can use that as the "time base."

Now make a counter, 4 bits wide so it can count up to 10. When it reaches 10 you want to stop counting and stop the LED blinking; that signal is simply an AND gate to go hi on the count of 10, or 1010 in binary. A singly 2-input AND will do this as all you need do is test when the 2nd and 4th bits are high.

Use that signal to both inhibit the clock to the counter and the signal to the LED. Note the logic for both is the same so the same gate can do both, just don't deive the LED and counter directly; use something for a driver for the LED so you don't load the logic. OR... load down the logic all you want but just use two gates, one for the clock and one for the LED.

You don't say how this thing is supposed to start, either by a button or by turning it on. Both have complications, like what is it supposed to do when the power goes on (with a button you may not want a blink at first). Either way, if you have a RESET to the counter you clear that to start a new sequence. Alternatively, you can LOAD a value of 10 to keep the counts off.

There are some ideas to get you going. One clock, one counter, and some gates.

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3. ### abhimanyu143 Thread Starter Member

Aug 25, 2014
211
1
Thank you for reply. I understood your idea. One clock,one counter, and some gates
can we replace gates by registers. because when we use 8051, simple we load the two registers than we create loop DJNZ

4. ### AnalogKid Distinguished Member

Aug 1, 2013
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The loop is just another way of incrmenting or decrementing a counter,and the 8051 non-zero test is the same as decoding the output of a counter to see when to reset it; gates do it in both cases. If you don't want to go through that, you can use a 4017 decade counter. It has a different construction, and can reset itself on any count without external gating.

ak

5. ### ian field Distinguished Member

Oct 27, 2012
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It never ceases to amaze me how some people reach for a micro just to blink a LED!

Someone even had a project published in one of the magazines (may have been the April issue) to programme a PIC to emulate a 555.

6. ### MikeML AAC Fanatic!

Oct 2, 2009
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Especially when you can buy these:
Flashing LEDs

7. ### abhimanyu143 Thread Starter Member

Aug 25, 2014
211
1
we can design circuit in different way. I am not really going to make LED blinking project without MCU. I am asking for basic concept . how to incrment or decrement a counter, ? when we make LED project using 8051 MCU they use counter , and two registers.
I just want to follow architecture of 8051.thats why I use one clock, one counter and two registers

8. ### AnalogKid Distinguished Member

Aug 1, 2013
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1,251
Something to consider is that the 8051 uses registers not because they are the best way, but because registers are all it has to work with. This is an excellent example of Abraham Maslow's comment about tunnel vision. Emulating microcontroller methods with discrete components rarely teaches anything useful, and misses an opportunity to experience diversity.

ak

9. ### ErnieM AAC Fanatic!

Apr 24, 2011
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At Digikey, single quantity I can get an LM555 for 45 cents. For another nickle I can get a PIC and not worry about the RC timing network.

You do the math.

10. ### ian field Distinguished Member

Oct 27, 2012
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There are a few things a 555 can do that a micro can't. If you think outside the box you can get the 555 to do tricks its designer never imagined. A micro is far less robust generally and won't take much in the way of abuse.

11. ### Stuntman Active Member

Mar 28, 2011
181
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Ha, you beat me to it.

I do, however, empathize with Ian's point.

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12. ### ian field Distinguished Member

Oct 27, 2012
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A PIC can be as small as a SMT transistor, albeit with at least 5 pins - its horses for courses, obviously the capabilities of a flash micro leave a 555 in the dust, but I've done projects that simply wouldn't have happened with a micro.

I still think the project to emulate a 555 with a PIC was probably published in an April issue.

13. ### Stuntman Active Member

Mar 28, 2011
181
47
In re-reading, I didn't mean for my post to sound condescending.

What I was hinting at, is I am absolutely dumbfounded with how cheap they can sell an mcu with that much functionality. That said, I try to stay up on some analog magic when I can.

And I agree, doing everything in software is not necessarily the right answer.