Version 4
SHEET 1 940 680
WIRE -176 -64 -176 -80
WIRE 384 16 384 -16
WIRE 192 32 176 32
WIRE 288 32 272 32
WIRE 176 80 176 32
WIRE 208 80 176 80
WIRE 160 96 128 96
WIRE 208 96 208 80
WIRE 288 96 288 32
WIRE 288 96 256 96
WIRE 384 96 384 80
WIRE 128 112 128 96
WIRE 160 112 160 96
WIRE 288 112 288 96
WIRE -64 128 -176 128
WIRE 96 128 16 128
WIRE 192 144 160 144
WIRE 288 144 272 144
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 -176 -64 0
FLAG 160 112 0
FLAG 128 176 V+
FLAG 384 -16 V+
FLAG 288 112 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 sw 288 144 R90
SYMATTR InstName S1
SYMATTR Value Switch
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 18k
SYMBOL res 0 208 R0
SYMATTR InstName R3
SYMATTR Value 1k
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 32 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 -32 56 VBottom 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value PULSE(0 5 0 0 0 50µ 100µ)
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 2 0.1