Version 4
SHEET 1 880 680
WIRE 80 32 -48 32
WIRE 272 32 80 32
WIRE 80 80 80 32
WIRE 272 80 272 32
WIRE 272 192 272 144
WIRE 80 208 80 160
WIRE 208 240 128 240
WIRE 272 304 272 288
WIRE 320 304 272 304
WIRE -48 320 -48 32
WIRE 80 336 80 288
WIRE 272 400 272 384
FLAG -48 400 0
FLAG 80 400 0
FLAG 272 400 0
FLAG 320 304 SHUNT
SYMBOL res 64 64 R0
SYMATTR InstName R1
SYMATTR Value 820
SYMBOL diode 64 336 R0
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMBOL npn 208 192 R0
SYMATTR InstName Q1
SYMATTR Value BC847C
SYMBOL LED 256 80 R0
SYMATTR InstName D2
SYMBOL voltage -48 304 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 5
SYMBOL res 256 288 R0
SYMATTR InstName R3
SYMATTR Value 75
SYMBOL Pot&Sw\\pot 64 304 M180
WINDOW 0 36 32 Left 2
WINDOW 3 36 88 Left 2
SYMATTR InstName U1
SYMATTR Value Rt=1K set={VAR}
TEXT 112 48 Left 2 !.step param VAR 0 1.0 .01
TEXT 120 72 Left 2 !.op