Description
Schematic diagram
PCB layout

Part list:

U1 - MRDS192
U2 - 78L05

R1 - 33k
R2 - 16k
R3 - 8k2
R4 - 3k9
R5 - 2k
R6 - 1k
R7 - 820R
R8, R9 - 4k7 (2 k if driven by COM port)
R10 - trimmer 500R

C1 - 10n (ceramic)
C2 - 22n (plastic)
C3, C4 - 27p (ceramic)
C5, C6 - 100n (ceramic)

L1 - 330 uH (radial, 09P-331K)

Y1 - crystal 4.332 MHz