Author Topic: Simple electronics help  (Read 651 times)

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Marty Machine

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Re: Simple electronics help
« on: March 02, 2012, 10:59:12 PM »
The 555+4017 are a classic led chaser design from waaaaay back....

Your pinouts are correct, and outputs will only briefly pulse on/off then move to the next pin....

Since you are using all 10 outputs, there's no need to force a reset, as it will auto-loop and count 1-10 again & again....

If you wanted say 5 leds to chase and repeat, you would wire the 6th output pin back onto the reset pin, the chip will reset immediately after the 6th led flashed and resume at led #1 again.

The 4017 used to drive STANDARD (5mA) leds back in the day with no trouble at all, but these days all the high-bright leds needs 20-50mA and i don't think the 4017 can source that much current on it's outputs. (i don't have the exact specs on hand).

Instead of using 10x transistors, you could use a buffer IC, such as the (cmos) 4049 or 4050, although you'd need a couple to cater for 10 outputs, although once again you'd need to confirm their current drive.
I'd prefer to use a higher current drive from a ULN2803 (8 outs), at least then you could drive relays or hi-watt leds and/or globes with no troubles in future ;-)

Hope it helps.
MM.