A Very Useful Timed Beeper Circuit Schematic
This circuit is intended for alerting purposes after a certain time
is elapsed. It is suitable for table games requiring a fixed time to
answer a question, or to move a piece etc. In this view it is a modern
substitute for the old sandglass. Useful also for time control when
children are brushing teeth (at least two minutes!), or in the kitchen,
and so on.
- R1 = 220R
- R2 = 10M
- R3 = 1M
- R4 = 10K
- R5 = 47K
- C1 = 100nF-63V
- C2 = 22µF-25V
- D1 = 1N4148
- D2 = 3mm. Red LED
- Q1 = BC337
- P1 = SPST Pushbutton (Start)
- P2 = SPST Pushbutton (Reset)
- PS = Piezo sounder (incorporating 3KHz oscillator)
- B1 = 3V Battery (2 AA 1.5V Cells in series)
- IC1 = CD4081 Quad 2 input AND Gate IC
- IC2 = CD4060 14 stage ripple counter and oscillator IC
- SW1 = 4 ways Switch (See notes)
Pushing on P1 resets IC2 that start oscillating at a frequency fixed
by R3 & C1. With values shown, this frequency is around 4Hz. LED D2,
driven by IC1A & B, flashing at the same oscillator frequency, will
signal proper circuit operation. SW1 selects the appropriate pin of IC2
to adjust timing duration:
- Position 1 = 15 seconds
- Position 2 = 30 seconds
- Position 3 = 1 minute
- Position 4 = 2 minutes
When the selected pin of IC2 goes high, IC1C drives Q1 and the piezo
sounder beeps intermittently at the same frequency of the LED. After
around 7.5 seconds pin 4 of IC2 goes high and IC1D stops the oscillator
through D1. If you want to stop counting in advance, push on P2.
- SW1 can be any type of switch with the desired number of ways.
If you want a single fixed timing duration, omit the switch and connect
pins 9 & 13 of IC1 to the suitable pin of IC2.
- The circuit’s reset is not immediate. Pushing P2 forces IC2 to
oscillate very fast, but it takes some seconds to terminate the
counting, especially if a high timer delay was chosen and the pushbutton
is operated when the circuit was just starting. In order to speed the
reset, try lowering the value of R5, but pay attention: too low a value
can stop oscillation.
- Frequency operation varies with different brand names for IC2.
E.g. Motorola’s ICs run faster, therefore changing of C1 and/or R3
values may be necessary.
- You can also use pins 1, 2, 3 of IC2 to obtain timings of 8, 16 and 32 minutes respectively.
- An on-off switch is not provided because when off-state the circuit draws no significant current.