help with a school project

[telephoneman]

what i am trying to do is take a steady 12 volt supply and make seven LEDs turn on one at a time and then go out one at a time at 1/2 hz cycle. attached is the schematic that i made. I was unable to find a lm3915 chip to simulate on multisim but i built one for the drawing. Any ideas on how to make this thing work would be greatly appreciated

 

[audioguru2]

Hi Telephone Man,
Are all the LEDs lighted all the time?

Look at a tutorial about how the 555 works and you will see that the voltage on the capacitor will go from 1/3rd of the supply (4.0V) to 2/3rd of the supply (8.0V).

Look at the datasheet or at a tutorial about the LM3915 and you will see that you have it starting to light the 1st LED when the input voltage is slightly above 0V and lighting the 10th LED when the input voltage is at 1.25V. You need to change the voltage when the 1st LED lights to 4.0V and change the voltage when the last LED lights to 8.0V.

 

[telephoneman]

yeah, all the leds are lit. I put in a voltage diver circuit and placed my ref low on 4 volts and ref high on 8 volts and it didn't seem to make a difference.

 

[telephoneman]

like this?

 

[audioguru2]

You saved your schematic as a fuzzy JPG file type instead of a very clear GIF or PNG file type.

Pin 7 is the output of an adjustable voltage reference. Pin 8 is its adjustment terminal.
The two resistors are calculated similar to the LM317 adjustable voltage regulator.
You are forcing a voltage and current on these outputs which might have destroyed the LM3915 IC.

Look at the many example circuits and circuit explanations on the datasheet.
I think I calculated the resistors correctly, but the LEDs are the 1st and 10th instead of the ones in the middle you want.

 

[telephoneman]

yeah... i figured that the chip was fried. I am very new to this stuff so bare with me. i will try your resistor set up and post my results in a day or so. Thank you. and sorry about the JPG quality.