Economical Timebase Calibrator

An external timebase calibrator is a useful accessory for any oscilloscope it provides precise, visible time markers on the scopes horizontal sweep. Basically the circuit is a pulse generator with accurate time intervals between pulses i.e. the pulse repetition frequency. If the pulse width is made relatively small compared to the repetition rate and the pulse edges are steep then the output signal will look like a series of illuminated dots. These can be conveniently used to measure time periods on the screen just as you use the graduation marks on a ruler to measure length.

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Materials

994092-PCB.pdf

Component list

Resistors:
R1,R6 = 680Ohm
R2 = 5kOhm 6
R3 = 10MOhm
R5 = 6kOhm 8
R7 = 220Ohm
R8 = *
Capacitors:
C1 = 100pF trimmer
C2,C4 = 33pF
C3 = 10 pF
C5 = 100pF
C6 = 1nF
C7 = 10nF
C8 = 22nF
C10 = 220µ F 25V radial
C11,C13-C18 = 100nF
C12 = 47µ F 16V radial
Semiconductors:
D1 = 1N4001
IC1 = 74HC00
IC2,IC3,IC4 = 74HC390
IC5 = 74121
IC6 = 7805
Miscellaneous:
S1 = rotary switch, 2 poles, × 6 contacts
X1 = 1MHz quartz crystal
S2,S3 = toggle switch,1× change-over contact
K2 = 2-way PCB terminal block, lead pitch 5mm