Transcript Lab3

Counters
4017 decade counter (1-of-10)
What is a Counter?
• In digital logic and computing, a counter is a
device which stores (and sometimes displays)
the number of times a particular event or
process has occurred, often in relationship to
a clock signal
Types of counters
• Counters can be implemented quite easily using register-type
circuits such as the flip-flop, and a wide variety of designs exist, e.g:
• Asynchronous (ripple) counter – changing state bits are used as
clocks to subsequent state flip-flops
• Synchronous counter – all state bits change under control of a
single clock
• Decade counter – counts through ten states per stage
• Up–down counter – counts both up and down, under command of
a control input
• Ring counter – formed by a shift register with feedback connection
in a ring
• Johnson counter – a twisted ring counter
• Cascaded counter
Decade counter
4017 decade counter (1-of-10)
• A decade counter is one that counts in decimal digits,
rather than binary.
• The count advances as the clock input becomes high
(on the rising-edge). Each output Q0-Q9 goes high in
turn as counting advances.
• The reset input should be low (0V) for normal
operation (counting 0-9). When high it resets the count
to zero (Q0 high). This can be done manually with a
switch between reset and +Vs and a 10k resistor
between reset and 0V. Counting to less than 9 is
achieved by connecting the relevant output (Q0-Q9) to
reset, for example to count 0,1,2,3 connect Q4 to reset.
4017 decade counter (1-of-10)
• The disable input should be low (0V) for
normal operation. When high it disables
counting so that clock pulses are ignored and
the count is kept constant.
• The ÷10 output is high for counts 0-4 and low
for 5-9, so it provides an output at 1/10 of the
clock frequency. It can be used to drive the
clock input of another 4017 (to count the
tens).
4017 decade counter (1-of-10)
Traffic Light Project
Parts Required:
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resistors: 470 ×3, 22k, 100k
capacitors: 0.1µF, 1µF 16V radial, 10µF 16V radial
diodes: 1N4148 ×6
LEDs: red, amber (or yellow), green
1M preset, horizontal
555 timer IC, such as NE555
4017 counter IC
DIL sockets for ICs: 8-pin, 16-pin
on/off switch
battery clip for 9V PP3
stripboard: 20 rows × 21 holes
Traffic Light Project(cont..)
• This project operates red, amber and green
LEDs in the correct sequence.
• The time taken for the complete red - red &
amber - green - amber sequence can be varied
from about 7s to about 2½ minutes by
adjusting the 1M preset
• The 555 astable circuit provides clock pulses
for the 4017 counter which has ten outputs
(Q0 to Q9).
Traffic Light Project(cont..)
• Each output becomes high in turn as the clock
pulses are received. Appropriate outputs are
combined with diodes to supply the amber
and green LEDs.
• red LED is connected to the ÷10 output which
is high for the first 5 counts (Q0-Q4 high), this
saves using 5 diodes for red and simplifies the
circuit.
Traffic Light Project(cont..)
Circuit diagram