Re: 555 Problem - New

> If I remove the LED to (-). The other LED blinks for a while
> hen goes steady on. If I put the (-) one back and remove
> the one connected to (+) it too blinks for a while then goes > to solid on.

> Any ideas?

I would check your battery voltage to make sure it's not dead or below
6 volts. Also you are wasting power using a 1 K resistor for R1. When
pin 7 goes low to discharge the capacitor, it supplies 9 milliamps into
R1, so you have about a constant 4.5 mA loss in R1. I would use 10K for
R1 and 100K for R2 and maybe 22uF for C. That will give you same times
and save 5 milliamps.

There is also another problem that the 555 output will not move all the
way to +9. It will only get within 2 volts, or about 7 volts on a 9
volt battery. This means when the 555 output moves high to 7 volts, you
still have 2 volts across the LED and resistor connected to +9 which
may turn it on. Also, you need a larger resistor for the LED connected
to +9. For 15 mA current, the resistor will be 470 ohms, not 330.

There is a CMOS version of the 555 (I forget the number) that moves all
the way from ground to +V on the output. The dual LED circuit may work
better with that part and both resistors can be 470 ohms.

Another idea is to use 2 LEDs in series connected to +9 with a 330 ohm
resistor. That way the two LEDs cannot light with only 2 volts applied.


Another idea is to use ultra bright LEDs that are bright at a few
milliamps so the little 9 volt battery lasts longer. Raise the LED
resistor values about 5 times and the battery will last much longer.

-Bill

.

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