Use caution with Ra. I recommend as a "rule of thumb" to always have at a minimum 100 Ohms per 1v of Vcc. If Vcc=6v, use 600 Ohms or more. If you go much lower than that, you will let the magic smoke out of the 555 timer.

1N914 diodes are equivalent to 1N4148 diodes. They have a maximum current rating of 100mA. As the current through them increases, so does their Vf (forward voltage).

See the attached graph, which illustrates the Vf of a typical 1N914/1N4148 over a range of current flow.

 

I changed the power supply from a 6v batt to a 9v batt. It still doesnt pulse but it is a lot brighter.

 

The LED resistor needs to be around 150Ω or 180Ω with a 9V battery. Did you use a variable resistor on one of the 555's for Rb? You will need to.

 

So use the 1K variable trim pot for Rb and the 1K for Ra or would i need a different value for Ra.

 

BRB, I'm drawing the new schematic. Words tend to confuse where pictures do not.

*******

OK, Note I showed two ways of laying out the variable resistor network.

R4 should be a 10 turn pot for best results.

 

I rebuilt everything using the new schematic and it is still doing the same thing stays on bright. Im using the 9v for power supply. I have adjusted the trim pot both ways and still no change.

 

These oscillators are well within the hearing spectrum. If you probe them with any kind of audio detector (such as headphones) you can hear the tone on pin 3, which should be the same for both.

Also, some newer DVMs have freq counters. These oscillators will be basically the same frequency, somewhere around 650 Hz, with a difference of about ½ Hz from each other.

Which variation did you use, R6=9.1KΩ, or R6=10KΩ with R5 in parallel? You used the 556 variation?

 

i used the 556 with R6 as a 10k. I even tried swapping R6 out with a 9K like the variation and it still does the same thing.

 

Shouldnt the frequency be around 65hz to be seen by the human eye for the pulse rate?

 

OK, I just finished building the sucker myself. I'm embarrised as to what the problem is. The oscillators are coupling to each other, that is to say, they get close enough to the same frequency they lock in on a common tone.

The answer is bypass capacitors, using .1µF to 1.0µF on Pins 3 and 11 to ground, and add a large capacitor to the battery, 220µF as too small, but a 1000µF worked. I'm going to have to take a long hard look at that circuit again, it looks like it could use a voltage regulator to clean up the power. 9V batteries are good sources, but they don't have much omph, so any noise shows up on the power supply lines extremely easily.

I apologize for the hassle.

As for theory, you don't actually see these frequencies, you see the difference between them. If one oscillator is 670Hz (measured frequency) and the other is 670.5Hz, you see the .5Hz difference.

 

No problem Thanks for the help. So a 1uf cap at pin 3 and 11 and then 1000uF at Vcc.
I have a 1amp voltage regulator (radio shack Pn 276-1770) would that work to help clean the voltage up? if so what the best way to integrate it into the circuit.

 

No problem thanks for the help. so a 1uF cap at pins 3 and 11 with another at Vcc sould cure the problem? What about using a 1amp Voltage regulator (Rc Pn 276-1770) would this work to clean up the voltage?
i need to get a few more caps tomorrow all i have left are 10uF what would i need to change to add 2 more leds in series or parallel with this one?

 

On Intersil's datasheet for their ICM7555 Cmos 555 they show a graph of the 400mA supply current spikes caused by an ordinary 555 and the very low supply current spikes caused by their Cmos 555.
No wonder the ordinary 555 oscillators lock to the same frequency.

 

It sounds like using two 555 timers may be better than using one 556. It might help to put a 10 ohm resistor in series with power coming to the 555. Then use a large valued capacitor say 10 uF and a 0.1 uF cap as bypass filters right across each of the two 555 timers. That will give a bit more isolation between the two 555 timers.

hgmjr

 

When it wasn't working like I was trying for. the same output freq made me think in the back of my head that they were canceling each other out. I havent messed with alot of 555/556 so this was a new project for me. I will have some pics of this when it working.

 

Truth, AudioGuru's circuit is looking better and better. There are lots of ways to do this, and I do mean lots.

I think I've run into an interesting difference between theory and practice. It can work, but it needs tweaking. I liked hgmjr's idea, I hereby steal it and make it my own.

But seriously, I reviewed the thread, I didn't see how long you were thinking a cycle would take. I'll sketch up a few more ideas for you so you can use the existing parts you already have. Until you define it I'm thinking a cycle every two seconds.

 

two second would be cool. I have 1 10uf cap left and resistors from 1ohm all the way up. im going to make a second trip to radio shack tomorrow to get some more caps.

 

Here is another idea:

R1 and R2 can be reduced to 1KΩ if the caps are upped to 2,200µF.

R1 is the cycle rate (how many seconds a flash lasts), and R2 is the fade rate. If R3 is adjusted to 91Ω it can go down to 6V with no problem, it may even manage 5V (R3=39Ω). It will go to 3 seconds per flash to faster than the eye can see, Set both pots for max before powering up, and don't take R1 to it's minimum value or the 555 will get hot.

This is a variation of the 555 Hysteretic Oscillator, R2 and C2 both slowly charge and discharge, Q1 and Q2 are basic transistors, 2N2907 or 2N3904 (almost any PNP transistor) will work.

 

Truth, AudioGuru's circuit is looking better and better. There are lots of ways to do this, and I do mean lots.

I think I've run into an interesting difference between theory and practice. It can work, but it needs tweaking. I liked hgmjr's idea, I hereby steal it and make it my own.

But seriously, I reviewed the thread, I didn't see how long you were thinking a cycle would take. I'll sketch up a few more ideas for you so you can use the existing parts you already have. Until you define it I'm thinking a cycle every two seconds.

Bill,

I am honored that you think one of my ideas is worth adopting as your own. I hereby relinquish all claims to it. Take it and run with it.


hgmjr

 

/hijack mode on/

The basic idea of the dual oscillator is definately going to make it the 555 projects. It is an excellent way to introduce someone to the concept of hetrodyne, as well as being interesting visually. It could be one of the better ideas I've had. You'll note the diode bridge strongly resembles a balanced modulator.

/hijack mode off/