Component List

Resistors

R1,R2,R3 = 330 Ω, 0.25 W, 5 %
R4 = 4.7 kΩ, 0.25 W, 5 %
R5 = 0 Ω, place wire, see text
R6 = 0 Ω, place wire for 5 V or leave open, see text
R7 = 1.5 kΩ, 0.25 W, 5 %

Capacitors

C1,C2 = 100 nF, 50 V, 10 %, X7R, lead spacing 5 mm
C3 = 100 µF, 25 V, optional , not mounted, see text

Semiconductors

D1 = BAT85, DO-35
T1 = BC327, PNP, TO-92
LED1 = LED red, 5 mm
LED2 = LED yellow, 5 mm
LED3 = LED green, 5 mm
 

Other

MOD1 = 1x10 SIL header, female, split in 1x4 and 1x5 (see Text)
MOD1 = MH-Z19C, version 400-5000 ppm, pins on bottom
MOD2 = Wemos D1 mini with 2x  1x8 SIL header
S1 = switch with built-in LED (momentary on, self-reset, blue circle)
Enclosure PP73BL, Supertronic
BZ1 = DC buzzer, 5 V, pitch 5 or 7.62 mm, diam. 14 mm max
heat shrink tube, I.D 2.4 mm, 20 cm
LED housing, for 5 mm LED (LED1..3), Black
FAN 5 VDC, 30x30x10.5 mm
12-pin male SIL header

PCB 210043-1 v2.0

Thin stranded wire to connect LEDs and switch:

stranded wire, 0.25 mm², black (2x8.5+12 cm)
stranded wire, 0.25 mm², red  (8.5+12 cm)
stranded wire, 0.25 mm², yellow (12 cm)
stranded wire, 0.25 mm², green (12 cm)
stranded wire, 0.25 mm², blue (8.5 cm)