led Flash unit single flash

Toss all parts of the circuit and use a switch to drive a NPN one-shot which drives the LED. Parts: one capacitor, two resistors, one switch and one 3V battery.

--- Since the circuit the OP references is a dual array with one set of LEDs ON while the other set is OFF, chances are that he meant to flash for one _cycle_, which would mean both sets of LEDs were OFF before the switch was made, then, when the switch was made, one set would light,the second set would light as soon as the first set went OFF, then when the second set went OFF both sets would stay OFF until the switch was once again made.

If that's the case, your circuit wouldn't work since, after the timeout, one set of LEDs would light and stay that way.

Try this: (View in Courier)

Vcc>-+-----+---+--------------+----+ | | | U1a | | U1b | | | +------+ | | +------+ [RtA] [10k] | | _ | [RtB] | | _ | | | +-|1R | | +-|1R | | | | | | | _ | | +----O|1A 1Q|-+---|-----O|2A 2Q|-+ | | | | | | | | | +-----|-----|1Rt | | +------|2Rt | | | | | | | | | | | | | +--|1A | | | +--|2A | | [CtA] | | | | | [CtB] | | | | | | O +--|1Ct | | | +--|2Ct | | | | O | +------+ | | | +------+ | | S1| | 4538/2 | | | 4538/2 | GND>-+-----+--+------+----|---+---+------+ | | | | | | [1k] | [1k] E | E | NPN B--+ NPN B--+ C C | | |K |K [LED] [LED] | | [R] [R] | |

+V>------------------+-------------------+

--- JF

Google "555 one shot" or "555 monostable"

Ed

Ed,

Maybe you should have looked at the link first, it already uses an 555.

:-\

h

PS: To the OP, use a PIC.

--
Oops, haste makes waste...


Vcc>-+-----+---+---------------+----+
     |     |   |     U1a       |    |     U1b
     |     |   |  +------+     |    |  +------+
   [RtA] [10k] | 3| _    |   [RtB]  |13| _    |
     |     |   +-O|1R    |     |    +-O|2R    |
     |     |     4| _    |8    |     12| _    |10
     |     +-----O|1A  1Q|-+---|------O|2A  2Q|-+
     |     |     2|      | |   |     14|      | | 
     +-----|------|1Rt   | |   +-------|2Rt   | |
     |     |     5|      | |   |     11|      | |
     |     |  +---|1A    | |   |   +---|2A    | |
   [CtA]   |  |  1|      | | [CtB] | 15|      | |
     |   | O  +---|1Ct   | |   |   +---|2Ct   | |
     |   | O  |   +------+ |   |   |   +------+ |
     |   S1|  |    4538/2  |   |   |    4538/2  |
GND>-+-----+--+-------+----|---+---+-------+    |
                      |    |               |    |
                      |   [1k]             |   [1k]
                      E    |               E    |
                   NPN  B--+            NPN  B--+
                      C                    C
                      |                    |
                      |K                   |K
                    [LED]                [LED]
                      |                    |
                     [R]                  [R]
                      |                    |
+V>-------------------+--------------------+

So, reconfigure it into one-shot mode.

No, no, no! No "Use a PIC" posts allowed without a full schematic and program listing. ;-)

Cheers! Rich

OK, if the OP is still follow this thread.

"to make it flash only once instead of repeating the flash? "

Please tell us how does this "flash only once" get triggered ?

The original schematic was to flash the LEDs as soon as the power is turned on.

Is this how you want yours to "flash only once" as well ??

1) POWER is OFF 2) POWER is applied (specify time to wait) 3) First row of LEDs turns ON (specify time wait) 4) First row of LEDs turns OFF (specify time wait) 5) Second row of LEDs turns ON (specify time wait) 6) Second row of LEDs turns OFF (specify time wait) 7) wait in IDLE loop ( waits forever )

Please answer these questions and I will create your PIC timer for you.

hamilton

Actually, I did, before posting my reply. I figured that he already has a 555, and might want to use it as a one-shot for his project. I wonder what made you think I didn't look? Perhaps you weren't aware that a

555 could be configured to produce a single pulse?

Ed

Sorry Ed,

I know you know, but some answers are just too simple.

As my earlier post to the OP, how does the "to make it flash only once instead of repeating the flash? " really works.

h

Well, you've completely lost me. Your first sentence refers to ... what? Are you saying that using a 555 as a one shot is "just too simple"?

Your second sentence is not understandable. Are you asking how a 555 configured as a one shot works?

Finally, you mention your earlier post to the OP, but all I see from you are posts to me and to Rich Grise. Can you paste it into your reply so I can see it? Perhaps the newsgroup provider I use (news.eternal-september.org) dropped it.

Ed

Here is the post where I asked the OP for more info about his application.

But, it looks like the OP is gone.

h

No mods required...hook it to a 12V battery, might flash once...