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From: "Edward Rawde" <invalid@invalid.invalid>
Newsgroups: sci.electronics.design
Subject: An actual circuit
Date: Thu, 23 May 2024 15:35:00 -0400
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I was having a conversation with a younger person who seemed to be of the 
view that to make an LED flash you would need something to decide when it 
should be on or off. So that would be some kind of software or digital 
system.

This reminded me of when, in my teen years, I was curious about how slow I 
could make an LED flash without using any expensively large capacitors.

I built a circuit like the one below but it needed a kick starter (another 
resistor, larger capacitor and diode) to make it go at power on.

LTSpice says the circuit below starts up with only a little imbalance in the 
values of R2 and R6 but how can I be sure that a real circuit will do this 
when component tolerances are taken into account?

Watch out for line wraps and 0.1 uF character encoding issues.

Version 4
SHEET 1 1396 772
WIRE -144 -512 -384 -512
WIRE -16 -512 -144 -512
WIRE 496 -512 -16 -512
WIRE 624 -512 496 -512
WIRE -144 -432 -144 -512
WIRE -16 -432 -16 -512
WIRE 496 -432 496 -512
WIRE 624 -432 624 -512
WIRE -208 -272 -272 -272
WIRE -144 -272 -144 -368
WIRE -144 -272 -208 -272
WIRE -16 -272 -16 -352
WIRE 32 -272 -16 -272
WIRE 64 -272 32 -272
WIRE 176 -272 128 -272
WIRE 352 -272 304 -272
WIRE 448 -272 416 -272
WIRE 496 -272 496 -352
WIRE 496 -272 448 -272
WIRE 624 -272 624 -368
WIRE 688 -272 624 -272
WIRE 752 -272 688 -272
WIRE -384 -256 -384 -512
WIRE -16 -192 -16 -272
WIRE 496 -192 496 -272
WIRE 96 -128 32 -128
WIRE 176 -128 304 -272
WIRE 176 -128 96 -128
WIRE 304 -128 176 -272
WIRE 384 -128 304 -128
WIRE 448 -128 384 -128
WIRE -144 -48 -144 -272
WIRE 624 -48 624 -272
WIRE -16 0 -16 -96
WIRE -16 0 -80 0
WIRE 496 0 496 -96
WIRE 560 0 496 0
WIRE 176 16 176 -128
WIRE 304 16 304 -128
WIRE -16 32 -16 0
WIRE 496 32 496 0
WIRE -144 96 -144 48
WIRE 624 96 624 48
WIRE -384 208 -384 -176
WIRE -144 208 -144 176
WIRE -144 208 -384 208
WIRE -16 208 -16 112
WIRE -16 208 -144 208
WIRE 176 208 176 96
WIRE 176 208 -16 208
WIRE 304 208 304 96
WIRE 304 208 176 208
WIRE 496 208 496 112
WIRE 496 208 304 208
WIRE 624 208 624 176
WIRE 624 208 496 208
WIRE -384 240 -384 208
FLAG 32 -272 leftd
FLAG 448 -272 rightd
FLAG 96 -128 leftg
FLAG 384 -128 rightg
FLAG -384 240 0
FLAG -208 -272 leftled
FLAG 688 -272 rightled
SYMBOL njf 448 -192 R0
WINDOW 0 0 -11 Left 2
WINDOW 3 -59 98 Left 2
SYMATTR InstName J1
SYMATTR Value 2N3819
SYMBOL njf 32 -192 M0
WINDOW 0 7 -9 Left 2
WINDOW 3 -64 100 Left 2
SYMATTR InstName J2
SYMATTR Value 2N3819
SYMBOL npn 560 -48 R0
WINDOW 0 61 31 Left 2
WINDOW 3 61 69 Left 2
SYMATTR InstName Q2
SYMATTR Value 2N3904
SYMBOL res -32 -448 R0
SYMATTR InstName R2
SYMATTR Value 2.7k
SYMBOL res 480 -448 R0
SYMATTR InstName R6
SYMATTR Value 3.3k
SYMBOL voltage -384 -272 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 12
SYMBOL cap 64 -256 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName C2
SYMATTR Value 0.1µ
SYMATTR SpiceLine V=25 Irms=0 Rser=0.0173 Lser=350p mfg="Würth Elektronik" 
pn="885012207072 WCAP-CSGP 0805" type="X7R"
SYMBOL res 480 16 R0
SYMATTR InstName R7
SYMATTR Value 1k
SYMBOL npn -80 -48 M0
WINDOW 0 57 22 Left 2
WINDOW 3 55 56 Left 2
SYMATTR InstName Q3
SYMATTR Value 2N3904
SYMBOL res -32 16 R0
SYMATTR InstName R3
SYMATTR Value 1k
SYMBOL res 160 0 R0
SYMATTR InstName R4
SYMATTR Value 10Meg
SYMBOL res 288 0 R0
SYMATTR InstName R5
SYMATTR Value 10Meg
SYMBOL res 608 80 R0
SYMATTR InstName R8
SYMATTR Value 150
SYMBOL res -160 80 R0
SYMATTR InstName R1
SYMATTR Value 150
SYMBOL LED 608 -432 R0
WINDOW 0 31 -3 Left 2
WINDOW 3 33 77 Left 2
SYMATTR InstName D7
SYMATTR Value NSCW100
SYMBOL LED -160 -432 R0
WINDOW 0 -32 3 Left 2
WINDOW 3 -113 67 Left 2
SYMATTR InstName D6
SYMATTR Value NSCW100
SYMBOL cap 352 -256 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName C3
SYMATTR Value 0.1µ
SYMATTR SpiceLine V=25 Irms=0 Rser=0.0173 Lser=350p mfg="Würth Elektronik" 
pn="885012207072 WCAP-CSGP 0805" type="X7R"
TEXT -344 240 Left 2 !.tran 1000