Need help adjusting times on 555 strobe.

[Deeg]

I've built a pretty standard LED strobe with the 555 IC using **broken link removed**. I'm using these resistors/caps:

R1 - 1k
R2 - 1k + 1M pot
C - 0.1uF
V = 9V battery

It works as it should and I'm pretty pleased with the results (I'm a electronics neophyte). I'd like to adjust the circuit so that the high signal is always ~ 0.01 seconds. According to the schematics in the link I can place a 1N4148 diode across the 7 and 6 pins of the 555. When I do this, however, the LED remains on and never flashes. I've tried different resistors/caps for R1 and C but the result is always the same.

Does anybody have a hint at what I might be doing wrong? I'm sure it's difficult without seeing my circuit but I'm hoping there's some common problem known to veterans.

 

[AllVol]

I've built a pretty standard LED strobe with the 555 IC using **broken link removed**.

When I click on your schematic, I'm seeing a monostable, or "one-shot" circuit. If that's what you have built, the use of a diode as you say will disrupt the action of the 555 and cause your problem.

Diodes are generally used with astable circuits to provide a near 50% duty cycle.

A single flash of .01 second duration will be pretty hard to see, don't you think?

 

[Thunderchild]

why not have a read of the 555 datasheet ? its full of example circuits, the rest is up to the imagination of the designer

 

[Deeg]

When I click on your schematic, I'm seeing a monostable, or "one-shot" circuit. If that's what you have built, the use of a diode as you say will disrupt the action of the 555 and cause your problem.

When I click on the link it displays the "basic astable oscillator" circuit. After the basic circuit there are two examples of circuits with different duty cycles. I've built the "120 seconds off/1 second on" circuit (but with the R1/R2/C values I listed above) but the LED doesn't turn off. I've double-checked my circuit multiple times and I've looked up different 555 schematic sources but haven't found anything that would indicate my problem. I'm hoping that it's something obvious to electronics experts, .e.g. I need to use a different diode at the frequencies I'm using.

A single flash of .01 second duration will be pretty hard to see, don't you think?

I'm planning on using my strobe in a demonstration of how a strobe can "freeze" rotational motion (like fan blades). The problem is that with a 50% duty cycle the "on" time is too long and the motion of items are blurred. I want to try with a shorter, fixed on time. I also want to dabble in multiple exposure photography.

 

[audioguru]

The "120 seconds off/1 second on" circuit will work fine if the 555 is a normal one, not a Cmos one, if the output of the 555 drives an LED connected to ground through a current limiting resistor, if the 9V battery is new and if the supply has a 100uF bypass capacitor.

Maybe you connected the diode backwards.
What is the part number of your 555?