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555cn led blicker making me mad

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LAN_403

811a vttc

Tue Aug 31 2010, 03:39AM

Registered Member #3097 Joined: Tue Aug 10 2010, 03:35PM
Location: Ontario Canada
Posts: 13

this is so stupid i can't get this to work. this is were i got the circuit

i'm not using cd4017 chip just the 555, i have the led coming out of pin 3 and going to ground, is this the right configuration, and i have 4.5 volts in because this setup will not osculate with anything more than that so i was told from this thread,

the led just stays on and does not blink?

i was gonna finish the circuit but i need to get the basic part running first any ideas?

Mike

Tue Aug 31 2010, 04:16AM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

my guess is that you have such a small time constant that the led is blinking but it is much too fast for your eye to see.

Either get a bigger cap for the 1uF cap (are you using 1uF actually?) on pin 6 or you could put the led on a long wire and wave it around and you might be able to catch it blinking

811a vttc

Tue Aug 31 2010, 01:19PM

Registered Member #3097 Joined: Tue Aug 10 2010, 03:35PM
Location: Ontario Canada
Posts: 13

its not osculating because i measured the voltage on pin 3 and set my multimeter to VAC it reads 0 but on VDC IT READS 4.5, and yes I'm using a 1uf tantalum capacitor is that my problem, because its not polorized?!?!?!?! my advice to electronic newbies don't buy stuff from radio shack its bad quality and they never have the right stuff so you end up getting something similar to compromise it but the the circuit doesn't work because its not exact and you just wasted lots of money!!!!!!grr

And my eyes can see VERY fast thing i can see a light bulbs flicker on 60hz, its drives me crazy!!

Renesis

Tue Aug 31 2010, 02:39PM

Registered Member #2028 Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319

I just ran a simulation on your circuit, and by adjusting the potmeter VR1 you should be able to get anything from 7Hz to 260Hz. Nothing wrong there. Now note that this circuit has a rather high frequency for led flashers, for you cant really distinguish anything over 30Hz. Since this circuit is designed to flash 10 leds in a sequence, and you are using only one led, then it would be reasonable to lower the oscillating freq by a 10fold. To do this simply replace C1 with a 10uF capacitor. (It does not matter if its polarized or not)

You say you measured 4,5V on the output. If you are powering the 555 with something near 9V, then this would most likely mean that the circuit is oscillating with 50% duty cycle at a high frequency. Dont trust your multimeters AC measurement to be able to detect the output of your 555, for the ac range on cheapo multimeters is designed only to read sinusoidal voltages at near line frequencies.

If you are absolutely, a hundred percent shure that the circuit is malfunctioning then you should go over and inspect every solder joint and look for short or open circuits. That could potentially cause the 555 to oscillate into the Mhz region, or even stop oscillating altogether.

MinorityCarrier

Tue Aug 31 2010, 03:12PM

Registered Member #2123 Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312

For the astable circuit, Pin 5 of the 555 typically has a .01uf capacitor 'tween it and ground.

811a vttc

Tue Aug 31 2010, 03:14PM

Registered Member #3097 Joined: Tue Aug 10 2010, 03:35PM
Location: Ontario Canada
Posts: 13

the input voltge is 4.5 volts, its not a cheap multimeter it cost $300, i checked all the connections and theres not unwanted bridges, and the connections are good.

klugesmith

Tue Aug 31 2010, 03:42PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Can you show us a -complete- schematic of your circuit, including the LED, current limiting resistor, orientation of tantalum capacitor, etc.? Maybe even a picture of your project, and a description of the 4.5V power supply. It's premature to whine about RS -- consider yourself fortunate to live in a country where you can buy resistors and capacitors over the counter.

Then, with a voltage reading on every pin (with respect to what?) the circuit can probably be debugged online. Don't forget to tell us the input resistance of your meter, and the measured resistance of VR1 as set.

The schematic you pointed to in OP is mostly high quality (for example, each component is given a reference designation). But it fails to show the critical connection between 555 pin 1 and the negative supply. There is one schematic "ground" symbol, on pin 1. Elsewhere, there is a net label with the name "GND". That would not automatically establish a connection in a CAD schematic capture program!

811a vttc

Tue Aug 31 2010, 04:56PM

Registered Member #3097 Joined: Tue Aug 10 2010, 03:35PM
Location: Ontario Canada
Posts: 13

you think its a bad schematic? i drew it out but just remembered my scanner doesn't work.~:-(

what would you suggest it looks like?

ok ran the circuit into circuit maker.

klugesmith

Wed Sept 01 2010, 12:15AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

OK, your problem is obvious.
[edit] no it's not, sorry, I was mistaken to say your ckt would give 99% duty cycle, which would be OK as a counter clock but look like LED was solidly on.

What is the average voltage (with respect to ground) on pin 5, and on the timing capacitor, and on the discharge pin?

p.s. Tantalum capacitors are a kind of electrolytic, and their polarity should be respected.

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