Actually recosindering it doesn't have to be reset (although if it
does, it doesn't matter). All that's important is that it generates
only a single one shot several second or so pulse and then should drop
to low, even though the trigger remains high. Once the trigger drops
to low, it should be able to generate another pulse when triggered
again. Alternatively, it could generate a single several second pulse
and then nothing until reset. It doesn't matter which as long as it's
capable of only generating one pulse while trigger remains high.
---
As long as your input pulse is longer than your output pulse, this
will work, and your output pulsewidth will be:
T = 1.4 Rt Ct
View in Courier:
+V
|
+-------+
|8 |
+---+---+ [1M]Rt
2|_ Vcc |3 |
IN>---+--[10K]--+--O|T OUT|---|----> OUT
| | | |6 |
| [1nF] | 555 TH|---+
| | 4|_ _|7 |
+---------|--O|R D|O--+
| | GND | |
| +---+---+ |+
| |1 [2.2µF]Ct
| | |
+-------+-------+
|
GND
Here's the LTSPICE circuit list, and if you don't have LTSPICE you
can download it for free from:
http://www.linear.com/designtools/software/
Version 4
SHEET 1 880 680
WIRE 304 48 -512 48
WIRE 416 48 304 48
WIRE 416 112 416 48
WIRE 32 176 -128 176
WIRE 304 176 304 48
WIRE 304 176 256 176
WIRE -336 240 -384 240
WIRE -224 240 -256 240
WIRE 32 240 -224 240
WIRE 320 240 256 240
WIRE 416 240 416 192
WIRE 416 240 320 240
WIRE 32 304 -32 304
WIRE 320 304 320 240
WIRE 320 304 256 304
WIRE 416 336 416 240
WIRE -384 368 -384 240
WIRE 32 368 -384 368
WIRE -32 416 -32 304
WIRE -512 432 -512 48
WIRE -384 432 -384 368
WIRE -224 432 -224 240
WIRE -512 560 -512 512
WIRE -384 560 -384 512
WIRE -384 560 -512 560
WIRE -224 560 -224 496
WIRE -224 560 -384 560
WIRE -128 560 -128 176
WIRE -128 560 -224 560
WIRE -32 560 -32 496
WIRE -32 560 -128 560
WIRE 416 560 416 400
WIRE 416 560 -32 560
WIRE -512 592 -512 560
FLAG -512 592 0
SYMBOL Misc\\NE555 144 272 R0
SYMATTR InstName U1
SYMBOL voltage -384 416 R0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PULSE(0 12 0 1e-6 1e-6 5 10 2)
SYMBOL res 400 96 R0
SYMATTR InstName R1
SYMATTR Value 1e6
SYMBOL cap 400 336 R0
SYMATTR InstName C1
SYMATTR Value 2e-6
SYMBOL voltage -512 416 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 12
SYMBOL res -48 400 R0
SYMATTR InstName R2
SYMATTR Value 1000
SYMBOL cap -240 432 R0
SYMATTR InstName C2
SYMATTR Value 1e-9
SYMBOL res -240 224 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R3
SYMATTR Value 10k
TEXT -464 592 Left 0 !.tran 20
