Cant get LED flasher to flash faster

[Mettam]

I built a LED flasher in Multisim which has a Potentiometer adjusting the timming of the flashing the problem is it doesnt matter what resistence I put on the POT it still flashes at the same timming.
Can someone tell me why I can't change the speed at which the LED flashes.

Thanks.

ps. I am unable to send as a attachment of the Multisim file, this forum wont accept files with a .ms9 extension

J.

[lacy]

I hate to state the obvious, but it is quite difficult to diagnose your problem without a circuit diagram or circuit file. I haven't posted any circuit files to this forum so I have no idea on how to do that.

[nestor-sg]

J., put your file inside a ZIP file (.zip)... or in case you cannot zip your file, just rename it to .txt and let us know...

[Mettam]

Here is the LED flasher circuit I built, I changed the .ms9 extension to .txt.
The problem is I cant see a visual differance in the flashing of the LED when I change the resitence.
Also I have seen Multisim comes with photo images of the components how do I get that feature turned on.

Thank you.

[nestor-sg]

J.,

I can't seem to be able to open your file correctly, with the change of extension it might have gotten corrupted. Anyways, I guess that was a bad idea...  can you put your file in a ZIP file?... that should do the job...

As far as the photo images, that's only a feature available in the academic versions of the product, and the components are available on the Master Database listed as 3D...

[Mettam]

Here it is again a a zip file.

[lacy]

O,K, First, be aware that I simulated this with 2001 version. Your LED does Flash faster as you crank the pot down, but it is just a slight variation. I calculated the frequency changes from about 15 Hz down to 13 Hz (if my math is correct). Not much of a difference, therefore may not be really noticiable with the LED, but you can see it with the O-scope (barely).

You may have to re-calculate your component values, especially the capacitor value, to get it to flash faster. Can you tell us at what flash rate and range of flash rates you would like to see? Maybe we can tinker with you values and come up with something to suit your need.

[Mettam]

Thanks for looking at this for me, I too noticed a slight variation of the flashing when I played with the POT but nothing like the variation when I built it on a bread board.
What components do I have to use to be able to see a much more noticable variation of flashing time.

Thanks again.

Justin.

[lacy]

Here's what I did. I used a 100K LIN Pot and reduced the capacitor to a .68uF. The .68uf will increase the frequency, but not too much while the 100K pot will give you a wider adjustment range. I calculated the frequencies as 16Hz-22Hz. This range is wider and is more noticiable in the simulator. If you need the a lower frequency range below 16 Hz, the pot may be sufficient to just increase the gap between the low and high frequency. Anyway, that is all I have and I hope this helps.

[Mettam]

Thanks Lacy, this you have been very helpfull.
Is there such a thing as an adjustable capacitor much like the potentiometer ?

Justin.