Morse Code Practice Oscillator
by Tony van Roon

Morse-code Practice

Parts List
 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
Additional Notes:
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