This simple timer can be set to run for different time settings (30 seconds to 4.5 minutes). Also, a musical note is played at the end of the set timing. Timer ICNE555 (IC1)is wired as an astable multivibrator (AVM).The AVM is set to 0.033Hz frequency using preset VR1. It means that the time period is around 30 seconds. The output of IC1 goes high for around 20 seconds and low for around 10 seconds. As it changes from low to high, decade counter IC CD4017 (IC2) is advanced by one count. IC2 has ten outputs Q0 through Q9. Switch S2 resets the counter which takes Q0 to logic high. Counting starts when switch S2 is released. Output Q1 goes high on the next positive-going pulse from IC1. IC2 is then incremented on each clock.
Outputs Q1 through Q9 of IC2 go high one-by-one at interval of 30 seconds. The rotary switch S3 selects one of these outputs and provides 3.1V power supply to melody generator IC When rotary switch S3 is connected to Q1 output of IC2 and reset switch S2 is pressed, a musical note is heard after a few seconds for 30 seconds. For positions 2 to 9, the silent period increases by 30 seconds at each step. At position 10 of rotary switch S3, the delay will be of four and a half minutes, followed by 30 seconds of music.
The best way to think about this is that positions 1 to 9 add 30-second delay each. If you let the timer continue to run, it repeats the tune every 5 minutes, irrespective of the setting of S3. The circuit runs on 6V, provided by four AA cells in a battery holder. A PP3-type clip is used to connect this to the circuit. S1 is a simple single-pole, UM66 (IC3). UM66 produces a musical signal on its output pin 1. The musical signal is amplified by transistor T1 and drives the speaker to produce the musical note. single-throw (SPST) switch . Assemble the circuit on a general- purpose PCB and enclose it in a suitable box. If you have a multimeter with a frequency-measuring facility, it would be ideal for setting the frequency of IC1 at pin 3 at around 0.033Hz. Check that IC2 outputs run through the correct sequence (each high for 30 seconds). Wire the loudspeaker to its terminal pins using external wires.
Fix rotary switch S3 in the front panel for selecting the time. The positions of rotary switch S3 can be labeled with stick-on tape labels. A simpler technique is to punch small discs from insulating tapes of various colours and stick these around the knob.
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pls give some additional details abt dat
ReplyDeleterotary switch used....