1. CIRCUIT
IDEAS
VARIABLE TIMER WITH MUSIC S.C. DWIV
EDI
 R.K. GORKHALI pulse from IC1. IC2 is then increment-
ed on each clock. Outputs Q1 through
T
his simple timer can be set to Q9 of IC2 go high one-by-one at inter- UM66 (IC3). UM66 produces a musical
run for different time settings val of 30 seconds. signal on its output pin 1. The musical
(30 seconds to 4.5 minutes). The rotary switch S3 selects one signal is amplified by transistor T1
Also, a musical note is played at the of these outputs and provides 3.1V and drives the speaker to produce the
end of the set timing. power supply to melody generator IC musical note.
Fig. 1: Circuit diagram of variable timer with music
Timer IC When rotary switch S3 is con- single-throw (SPST) switch .
NE555 (IC1) nected to Q1 output of IC2 and reset Assemble the circuit on a general-
is wired as an switch S2 is pressed, a musical note purpose PCB and enclose it in a suit-
astable multivi- is heard after a few seconds for 30 able box. If you have a multimeter
brator (AVM). seconds. For positions 2 to 9, the silent with a frequency-measuring facil-
The AVM is set period increases by 30 seconds at each ity, it would be ideal for setting the
to 0.033Hz fre- step. At position 10 of rotary switch frequency of IC1 at pin 3 at around
Fig. 2: Pin configurations
of UM66 and BC548 quency using S3, the delay will be of four and a half 0.033Hz.
preset VR1. It minutes, followed by 30 seconds of Check that IC2 outputs run
means that the time period is around music. through the correct sequence (each
30 seconds. The output of IC1 goes The best way to think about this high for 30 seconds). Wire the loud-
high for around 20 seconds and low for is that positions 1 to 9 add 30-second speaker to its terminal pins using
around 10 seconds. As it changes from delay each. If you let the timer con- external wires. Fix rotary switch S3 in
low to high, decade counter IC CD4017 tinue to run, it repeats the tune every the front panel for selecting the time.
(IC2) is advanced by one count. IC2 5 minutes, irrespective of the setting The positions of rotary switch S3 can
has ten outputs Q0 through Q9. of S3. be labeled with stick-on tape labels.
Switch S2 resets the counter which The circuit runs on 6V, provided A simpler technique is to punch small
takes Q0 to logic high. Counting starts by four AA cells in a battery holder. A discs from insulating tapes of various
when switch S2 is released. Output Q1 PP3-type clip is used to connect this to colours and stick these around the
goes high on the next positive-going the circuit. S1 is a simple single-pole, knob. 
1 1 2 • S E P T E M B E R 2 0 1 1 • E L E C T RO N I C S F O R YO U W W W. E F Y M AG . CO M