Greetings! well i found this knight rider schematic on the net, built it in multisim and it doesn't work, i have no idea why. could someone shed some light onto this for me. i am stumped

link to schematic:

http://www.uoguelph.ca/~antoon/gadgets/bfflash2.htm

attached is the multisim file i have zipped. thanks in advance for yourr reply!

warmest reguards,
Zac

 

Hi Zac, welcome aboard. Do you have a 'scope or logic probe? They'll help you trace the pulses from the oscillator [555]. Pay particular attention to the IC pins; make sure your 5V, common & appropriate signal pulses are connected or routed to the proper pins. If you used a "ready made, tried & true" PC board, the chance of wiring errors is much less & more likely a faulty part but also check for solder bridges & cold solder connections. Good luck.

 

Hi,

If you're using a non-CMOS based logic family, like 74LS, thn inputs taken high need to have a resistor in series. Use something like 10K to pull up pin 10 on the 74LS190, for instance.

The schematic is inadequate, too, in that all unsued inputs must be tied high or low to prevent the usused sections from going into destructive oscillation.

The 74LS190 is ok, with the exception of needing the resistor on pin 10. The 74LS76 needs pins 1 & 6 taken high (disables the clock inputs) and pins 4, 9, 12, & 16 tied to ground (disables the J & K inputs). Remember the resistors for pins 1 & 6.

Another note - if you're concerned with battery life, increase the size of R2 - R11. Taking them up to 360 ohms will still give you decent LED brightness, and cut battery drain significantly.

 

thank you both for your replies. you have been a big help to this newbie