Version 4
SHEET 1 1016 680
WIRE -16 -80 -176 -80
WIRE -176 -64 -176 -80
WIRE -16 -64 -16 -80
WIRE 384 16 384 -16
WIRE 384 96 384 80
WIRE 128 112 128 96
WIRE -64 128 -176 128
WIRE 96 128 16 128
WIRE 176 144 160 144
WIRE 288 144 256 144
WIRE 320 144 288 144
WIRE 96 160 80 160
WIRE 80 208 80 160
WIRE 384 208 384 192
WIRE 384 208 80 208
WIRE 16 224 16 128
WIRE 288 224 288 144
WIRE 384 224 384 208
WIRE -176 304 -176 208
WIRE 16 304 -176 304
WIRE 208 304 16 304
WIRE 288 304 208 304
WIRE 384 304 288 304
WIRE 208 336 208 304
FLAG 208 336 0
FLAG -176 -160 V+
FLAG 128 176 V+
FLAG 384 -16 V+
FLAG 128 96 V-
FLAG -176 16 V-
FLAG -16 -64 0
SYMBOL Opamps\\UniversalOpamp2 128 144 M180
SYMATTR InstName U1
SYMBOL LED 368 16 R0
SYMATTR InstName D1
SYMBOL voltage -176 112 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value {X}
SYMBOL npn 320 96 R0
SYMATTR InstName Q1
SYMBOL res 368 208 R0
SYMATTR InstName R1
SYMATTR Value 1
SYMBOL res 32 112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 680k
SYMBOL res 0 208 R0
SYMATTR InstName R3
SYMATTR Value 39k
SYMBOL res 272 208 R0
SYMATTR InstName R4
SYMATTR Value 1k
SYMBOL voltage -176 -176 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value 5
SYMBOL voltage -176 -80 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value 5
SYMBOL res 272 128 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 1k
TEXT -208 360 Left 2 !.tran 0 0.1 0.01 0.01
TEXT -216 400 Left 2 !.model Switch SW(Ron=2.5 Roff=10Meg Vt=0.8 Vh=-.5 Lser=10n Vser=.6)
TEXT 656 344 Left 2 !.step param X 0.44 1.96 0.52