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NNTP-Posting-Date: Thu, 23 May 2024 20:06:46 +0000
From: john larkin <jl@650pot.com>
Newsgroups: sci.electronics.design
Subject: Re: An actual circuit
Date: Thu, 23 May 2024 13:06:46 -0700
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On Thu, 23 May 2024 15:35:00 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:

>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.


The jfet astable is cute.

I had a high-voltage supply and wanted to blink an LED when there was
potentially dangerous voltage. I used a Supertex depletion fet to
charge a cap, and a diac to dump into the LED at about 1 Hz. Five
parts, including the LED.



>
>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
>