On Sat, 17 Sep 2005 18:09:58 -0500, John Fields
wrote:


Aaarrghhh!!!

I forgot the fourth LED, and the 7555's RESET is negative true...

7555
+-------+
+--|TH OUT|O-+
| |___ _| |
+-O|DIS R|O----Vcc
| +-------+ | Vcc
| | Vcc |
+----[POT]---+ +-----+ | [100K]
| | | _| | |
| 1M | +----|D Q| | |
| | | | _| | |
[1µF] +------| S|O------+----+
| | | | _| | | |
| | | +--|Q R|O--+ | [0.1µF]
| | | | +-----+ | | |
| | | | HC74/2 | | GND
+-[LED]--[R]-----+ | |
| | | | | |
| | | | +-----+ | |
| | | +--|D | | |
| | | | _| | |
| +------| S|O------+
| | | | _| | |
| | | +--|Q R|O--+ |
| | | | +-----+ | |
| | | | HC74/2 | |
+-[LED]--[R]-----+ | |
| | | | | |
| | | | +-----+ | |
| | | +--|D | | |
| | | | _| | |
| +------| S|O--+ |
| | | | _| | |
| | | +--|Q R|O------+
| | | | +-----+ | |
| | | | HC74/2 | |
+-[LED]--[R]-----+ | |
| | | | | |
| | | | +-----+ | |
| | | +--|D | | |
| | | | _| | |
| +-|----| S|O--+ |
| | | _| |
+-[LED]--[R]---+----|Q R|O------+
| +-----+
GND HC74/2

Also, a better way to run the LEDs would be off of the Q's. The
starting (and running) sequence could be made the same as if they
were being driven by the Q's by complementing the SETs and RESETs,
but there'd no LED loads on the Q's and, consequently, no problem
with logic input thresholds being load dependent.

Wire it up the way it's shown and if you have problems with it, post
back and I'll be happy to help you get it right.

---
More problems.

HC74's aren't supposed to run on 9V, so you'd have to use something
like a 78L05 to get that 9V down to 5V if you used HCMOS, and
recalculate the LED series R's.

--
John Fields
Professional Circuit Designer