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Topic: Will this PCB work for a 555 timer? (Read 4320 times) previous topic - next topic

alexgator

Hi all, first time posting, so apologies if I am doing something wrong.

I am designing a PCB that will blink 3 LEDs with an astable 555 timer. I followed the Instructables tutorial(http://www.instructables.com/id/555-Timer/step6/555-Timer-Astable-Mode-Circuit/).

Will this PCB design work?


Thanks in advance.


alexgator

I was planning on using a coin cell battery.

cmiyc

Looking at just a PCB is difficult to diagnose.   PCB and Schematic would be better.

Have you already built this circuit up on a breadboard (with the coin cell battery)?  I'm not seeing a current limiting resistors on the LEDs.  With a coin cell, that can only provide a few mA of current, you will probably only get a few minutes of life.

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7brian4

The 555 itself will need 4.5V min though, you will be using a few?

alexgator

Really only a few minutes?
https://www.sparkfun.com/products/338
"Blink an LED for weeks at a time"

Schematic:

Docedison

#6
Jul 08, 2013, 06:29 am Last Edit: Jul 08, 2013, 07:37 am by Docedison Reason: 1
There is a drop-in Cmos replacement for the NE/SE555 it's the ICM7555 radio shack sells them last I looked. I''ve attached the data sheet, It will work @ 3V according to the little I looked... I used them as clock generators for precision timers in the early 90's. National Semiconductor made a similar part at about the same time but for the life of me I can't remember the part #... Look for CMOS Timers and the 555 and that one, I think works to 2V. AT 2V operation your choices for led's are simple only the red will work at that low voltage and make very certain that you use the high output/high efficiency LED's because as I remember there isn't a 100 mA source sink current like the 555.    IHTH

Doc
--> WA7EMS <--
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I do answer technical questions PM'd to me with whatever is in my clipboard

7brian4

I'm curious about your switch also, you are just turning off the LED's but leaving the timer powered?

larryd

1. This PCB will not work as is. For example the battery + is shorted to -
2. Your circuit will not work, the schematic is wrong.
3. Before proceeding, always check your circuit out on a Prototyping board before you finalize you circuit/board.
4. Do not parallel your LEDs.
5. Use a TLC555 CMOS timer, should work at 3 Volts

As James C4S  suggests, you need resistors in series with the LEDS.
In this case one resistor for each LED (3Volt battery and 2V(led) at 10mA,  100 ohms should work).




No technical PMs.
The last thing you did is where you should start looking.

Docedison

After everything is said and done... Your board is a good first try. Whether it works or not depends on how important it is for it to work for you One thing I used to do was to draw a schematic from the board and then compare them... Mainly because sometimes netlisting software sometimes interprets symbols differently than we expect... And sometimes WE make errors. Sometimes it's useful to extract the netlist from the board to verify that autorouting did in fact go to 100% completion by comparing the two netlists. Sometimes the autorouter is a little optimistic... But that's because there are too many parts for the number of routing layers and ground-plane restrictions. Ground-planes are wonderful, Use them on both sides of the board. By making a ground plane you establish first the most difficult routing on the board and that is the ground.

Doc
--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

pwillard

#10
Jul 08, 2013, 07:45 pm Last Edit: Jul 08, 2013, 07:52 pm by pwillard Reason: 1
With proper parts placement, this could likely be a single sided board without too much extra effort.

I'm again reminded that using fritzing is like eating noodle soup with chopsticks... it sort of works... but kind of fails at the end.

polymorph

You really should have a fixed series resistor of at least 1k with the 10k potentiometer. Otherwise, you run the risk, nearly a certainty, that you'll turn the resistance down to the lowest setting and short pin 7 to V+.
Steve Greenfield AE7HD
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1ChicagoDave


MarkT

And there should be a decoupling capacitor on the supply near the 555 or 7555.  The 555 needs a lot of decoupling,
go with the CMOS 7555 if you can.
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