Morse Code Practice Oscillator
by Tony van Roon
R1 = 3K3 IC1 = 555 Timer IC
R2 = 15K S1 = Morse Keyer
P1 = 500 ohm LS = Loudspeaker, 8 ohm
C1 = 0.047uf (47nF)
C2 = 0.01uF (10nF)
C3 = 4.7uF/16v
The speaker (LS) can be any 8-ohm type up to 2-watts. C1 and C2 are ceramic capacitors. C3 is an electrolytic type.
IC1 is a CMOS MC1455P or equivalent. The cmos type consumes a lot less current when used
with the 9-volt battery, but if you don't want to spent the money then the LM555, NE555, etc. are fine too and are pin-for-pin
compatible with each other.
And obviously, S1 is your Morse-keyer. To get a more precise duty-cycle replace the components within the shaded gray area
from Fig. 1 with the ones in Fig. 2. The diode can be 1N4148 or equivalent. The zenerdiode is between 5.2 and 5.8 volt.
Ra and Rb are experimental to suit your personal taste. C is about the same.
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Copyright © Tony van Roon