Specifications

CONSTRUCTION
CONFERENCE TIMER
S.C. DWIVEDI
K. UDHAYA KUMARAN VU3GTH
tactile switches S2 and S3, with slide
switch S1 in 'set' position. Once the time
duration is preset, the same is displayed
in 7-segment LED displays (DIS.1 and
DIS.2).
As soon as the designated speaker
starts speaking, switch S1 is flipped
from 'set' position to 'start' position. The
displayed time will start decrementing
once a minute until it becomes 00, i.e
the unit digit (DIS.1) and tens digit
(DIS.2) both become zero. At this junc-
ture, the timer stops decrementing fur-
ther and an interrupted beep sound is
heard from the buzzer, indicating that
the time allotted to the particular
speaker is over.
In this circuit, IC5 (CD4060B, a 14-
stage binary counter with internal os-
cillator) is used for generation of the
basic timing pulses. Presets VR1 and
VR2 are required to be adjusted for ob-
taining approximately 1 Hz (1.0666 Hz,
to be more precise) pulses from pin 7
(Q4) of IC5, while the pulses from pin
15 (Q10) are available at the rate of one
pulse per minute. For countdown timer
D
uring a conference where speak-
ers are allotted different time
slots for completing their
speech, it is essential to use a suitable
conference timer which could be pro-
grammed for the given time slot. It
should not only provide indication as to
when the allotted time slot. It should
not only provide indication as to when
the allotted time is over, but also about
the leftover time at any given instant.
The conference timer presented here is
designed to incorporate all such facili-
ties and is expected to prove quite use-
ful.
This conference timer is just a 2-
digit (minutes) countdown timer which
can be preset from 01 minute to 99 min-
utes. The time duration is preset using
PARTS LIST
Semiconductors:
IC1, IC2 - CD4511B, BCD-to-7-
segment latch/decoder/
driver
IC3,IC4 - CD4510 BCD up/down
counter
IC5 - 4060B 14-stage counter/
divider/oscillator
T1-T4 - BC547 npn transistor
T5 - SL100 npn transistor
D1-D8 - 1N4007 rectifier diode
D9 - 5.1V zener
LED1 - Red LED
DIS1, DIS2 - LTS543 common-
cathode display
Resistors (all 1/4-watt, +_5% carbon, unless
stated otherwise):
R1-R14 - 470-ohm
R16-R18
R24, R28, R31 - 100-kilo-ohm
R19 - 100 ohm
R20, R27 - 33-kilo-ohm
R22, R23 - 10-kilo-ohm
R25, R30 - 22-kilo-ohm
R29 - 22-kilo-ohm
R26 - 470-ohm
VR1 - 50-kilo-ohm preset
VR2 - 1-mega-ohm preset
Capacitors:
C1 - 180pF ceramic disk
C2 - 47pF, 25V electrolytic
C3 - 001uF ceramic disk
C4 - 0047uF ceramic disk
Miscellaneous:
RL1 - Relay 6G, 100-ohm
S1 - DPDT slide switch
S2, S3 - Tactile switch
S4 - SPDT slide switch
PB - Piezo buzzer
Fig. 1: Circuit diagram of conference timer
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