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METRONOME
UPDATED:.11:55 29 June 2014
OPERATION NOTES

This circuit produces steady audible beats for keeping time when playing music.

The Tempo can be set from 41 beats per minute, up to an unusable 900.

The Pitch of the beat can be set on the second Astable

By adjusting the spike width on the Spike Generator with the preset, and changing pitch, a range of pops, taps, and wooden like hits can be created.

ASTABLE 1:
Set Range 1 - low frequency (0.7Hz-18Hz)
Use VR1 to alter the TEMPO of the beats.

+SPIKE GENERATOR:
Set the length of the beat with the preset - best setting is near minimum.

ASTABLE 2:
Set Range 3 - high Frequency (700Hz-18KHz)
Also try Range 2 - (31Hz-850Hz)
Use VR1 to atler the PITCH and produce a wide variety of sounds.


BLOCK DIAGRAM
CIRCUIT BLOX
EXPLANATION
Astable 1 is set at a low frequency to provide the Tempo, the output is about 2:1 mark/space ratio.

The Spike Generatpr creates a brief positive pulse on every rising edge of the first astable.

This pulse is connected to the "-Reset" input of the second Astable which is normally low, preventing any oscillation. The high pulse briefly enables the astable which is set at a high frequency to produce an audible tone.

This audible tone is amplified by the Darlington driver and in turn to a speaker. The tone is very brief so although there is a high current running through the speaker, its average current is actually quite low.

WARNING: Do not use a high quality speaker such as that for a home entertainment system as damage could occur. This is only suitable for small 0.3 to 1W loudpeakers.


TEACHING OPPORTUNITIES: DEVELOPMENT
Topics covered could be:
  • Sound generation using astables
  • Modulating signals and sound
  • Oscillators and associated termninology
  • Square, Sine, Triangle wave astables
  • Speaker design using electromagnetics.

Adding LEDs using a driver connected to the output of the Spike Generator. This can be used to observe the beat as well as hear it.

Projects developed:


    www.edutek.ltd.uk - Working Electronics For Students & Teachers