Version 4
SHEET 1 1536 680
WIRE 272 -192 272 -224
WIRE 384 -192 272 -192
WIRE 272 -160 272 -192
WIRE 384 -160 384 -192
WIRE -176 -80 -384 -80
WIRE 112 -80 -96 -80
WIRE 272 -48 272 -80
WIRE 384 -48 384 -96
WIRE 384 -48 272 -48
WIRE -384 -32 -384 -80
WIRE 272 -16 272 -48
WIRE -384 64 -384 48
WIRE -128 96 -432 96
WIRE 272 96 272 64
WIRE 272 96 -128 96
WIRE 832 96 832 80
WIRE -128 112 -128 96
WIRE -432 144 -432 96
WIRE -432 144 -480 144
WIRE 272 160 272 96
WIRE 832 192 832 176
WIRE -432 208 -432 144
WIRE -384 208 -432 208
WIRE -304 208 -320 208
WIRE -272 208 -304 208
WIRE -128 208 -128 176
WIRE -128 208 -192 208
WIRE -96 208 -128 208
WIRE 0 208 -96 208
WIRE 112 208 112 -80
WIRE 112 208 80 208
WIRE 144 208 112 208
WIRE 208 208 144 208
WIRE -96 272 -96 208
WIRE 144 272 144 208
WIRE -304 288 -304 208
WIRE -304 400 -304 352
WIRE -96 400 -96 336
WIRE 144 400 144 352
WIRE 272 400 272 256
FLAG 272 400 0
FLAG 144 400 0
FLAG -96 400 0
FLAG 272 -224 +V
FLAG 832 192 0
FLAG -384 64 0
FLAG 832 80 +V
FLAG -304 400 0
FLAG -480 144 in
SYMBOL npn 208 160 R0
SYMATTR InstName Q1
SYMATTR Value 2N3904
SYMBOL res 128 256 R0
SYMATTR InstName R1
SYMATTR Value 6k8
SYMBOL res 96 192 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 3k3
SYMBOL cap -112 272 R0
SYMATTR InstName C1
SYMATTR Value 100n
SYMBOL res -176 192 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R3
SYMATTR Value 22k
SYMBOL diode -144 176 M180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMBOL cap -320 192 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C2
SYMATTR Value 100n
SYMBOL res 256 -32 R0
SYMATTR InstName R4
SYMATTR Value 1k
SYMBOL res 256 -176 R0
SYMATTR InstName R5
SYMATTR Value 1k
SYMBOL LED 368 -160 R0
SYMATTR InstName D2
SYMATTR Value QTLP690C
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL voltage 832 80 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value 5
SYMBOL voltage -384 -48 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value PULSE(0 5 0 10n 10n 150u 300u)
SYMBOL res -80 -96 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R6
SYMATTR Value 33k
SYMBOL diode -320 352 M180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D3
SYMATTR Value 1N4148
TEXT 496 208 Left 2 !.tran 100m UIC
TEXT 504 400 Left 2 !.IC V(in) 5
TEXT 680 -96 Left 2 ;single-T latch by roelh on hackaday.io
TEXT 680 -64 Left 2 ;https://hackaday.io/project/7975-one-transistor-latch/discussion-104070
TEXT 496 304 Left 2 ;set IC to 5 for "reset" state
TEXT 496 352 Left 2 ;set IC to 0 for "set" state