Version 3
SHEET 1 892 692
WIRE -84 340 -84 400
WIRE 136 336 136 324
WIRE 136 352 136 368
WIRE 128 348 40 348
WIRE 136 368 136 372
WIRE 112 340 128 340
WIRE 112 340 112 312
WIRE 144 344 164 344
WIRE 164 312 164 344
WIRE 164 312 148 312
WIRE 128 312 112 312
WIRE -84 268 -12 268
WIRE -84 268 -84 260
WIRE -12 268 -12 288
WIRE -12 388 -12 396
WIRE -12 400 -44 400
WIRE -84 400 -84 416
WIRE -12 348 -12 356
WIRE -12 348 -12 308
WIRE 112 312 52 312
WIRE 40 348 -12 348
WIRE -12 356 -12 368
WIRE -12 396 -12 400
WIRE -44 400 -44 504
WIRE -44 400 -64 400
WIRE -44 524 -12 524
WIRE -12 504 -44 504
WIRE -44 504 -44 524
WIRE -12 544 -44 544
WIRE -44 544 -44 524
WIRE -84 320 -84 268
WIRE -12 400 52 400
WIRE 52 400 52 388
WIRE 52 368 52 312
WIRE 52 288 52 268
WIRE 52 268 -12 268
WIRE 52 312 52 308
WIRE -64 408 -64 400
WIRE -64 400 -84 400
WIRE 52 400 204 400
WIRE 204 400 204 384
WIRE 164 344 172 344
WIRE 172 344 204 344
WIRE 204 344 204 364
FLAG -84 260 v+
FLAG -84 416 v-
FLAG 136 324 v+
FLAG 136 368 v-
FLAG -64 408 GND
FLAG 172 344 out
FLAG 40 348 in
FLAG -12 356 in
FLAG -12 396 v-
SYMBOL VOLTAGE -84 316 R0
WINDOW 0 6 4 Left 0
WINDOW 3 10 14 Left 0
SYMATTR InstName Vbatt
SYMATTR Value 5V
SYMBOL RES 124 316 R270
WINDOW 0 19 14 Left 0
WINDOW 3 9 15 Left 0
SYMATTR InstName R2
SYMATTR Value 500k
SYMBOL res -16 284 R0
WINDOW 0 9 10 Left 0
WINDOW 3 9 19 Left 0
SYMATTR InstName R_adj
SYMATTR Value {R_ADJ}
SYMBOL bi -12 368 R0
WINDOW 0 -21 9 Left 0
WINDOW 3 -40 -5 Left 0
SYMATTR InstName B1
SYMATTR Value I=(V(in,v-) / {R_NTC} )
SYMBOL bi -12 504 R0
WINDOW 0 -21 9 Left 0
WINDOW 3 18 10 Left 0
SYMATTR InstName B2
SYMATTR Value I=(table({T_NTC}, 24.5, 22.5k, 32.3, 16.31k, 34.3, 14.46k, 36.1, 13.69k) )
SYMBOL bi -12 524 R0
WINDOW 0 -21 9 Left 0
WINDOW 3 18 13 Left 0
SYMATTR InstName B3
SYMATTR Value I={B_const}
SYMBOL res 48 284 R0
WINDOW 0 9 10 Left 0
WINDOW 3 9 19 Left 0
SYMATTR InstName R3
SYMATTR Value 20k
SYMBOL res 48 364 R0
WINDOW 0 9 10 Left 0
WINDOW 3 9 19 Left 0
SYMATTR InstName R4
SYMATTR Value 20k
SYMBOL res 200 360 R0
WINDOW 0 9 10 Left 0
WINDOW 3 9 19 Left 0
SYMATTR InstName R1
SYMATTR Value 20k
SYMBOL Opamps\TLC272_5_2 136 328 R0
WINDOW 0 4 8 Left 0
WINDOW 3 4 24 Left 0
SYMATTR InstName U1
SYMATTR Value TLC272_5_2
text 6 474 Left 0 ;.step param T_NTC list 24.5 32.3 34.3 36.1
text -160 436 Left 0 ;measured NTC data:\n \nB=3940K\nR_25=22k \n \nT [Celsius], R_NTC [Ohms]\n24.5 , 22.5k room\n32.3 , 16.31k hand\n34.3 , 14.46k\n36.1 , 13.69k
text 6 482 Left 0 !.step param T_NTC 24.0 40.0 0.1
text -34 382 Left 0 ;NTC
text -34 416 Left 0 !.params R_ref=22.5k T_ref=24.5 R_ref2=13.69k T_ref2=36.1\n.param B_const = (Log(R_ref / R_ref2)) / (1 / (273.16 + T_ref) - 1 / (273.16 + T_ref2))\n.param T_NTC = 20\n.param R_NTC = R_ref * Exp(B_const / (T_NTC + 273.16) - B_const / (T_ref + 273.16))
text 6 466 Left 0 !.op
text -58 236 Left 0 !.param R_ADJ=16k
text -58 248 Left 0 !.step param R_ADJ list 14k 16k 18k
text 70 222 Left 0 ;temperature bio-feedback amplifier
text 6 500 Left 0 ;I(B2) is R_NTC calculated (interpolated) from lookup table
text 6 524 Left 0 ;I(B3) is the B constant of the NTC in units of Kelvin (usual range from 2000..6000K)