www.nutsvolts.com/index.php?/magazine/article/november2010_QA
■ FIGURE 2
some searching before I got your
reply. After some exchanged emails,
etc., I bought one just for the 68
series 52 pin from Tech-Arts in
Canada ( www.technologicalarts.ca)
for $32. With the software link to
download and furnish a 12V ext
supply to program, he said it would
more than meet my needs.
TIMER PROJECT
trying to solve problems of others
and to learn more. I enjoy your
magazine; lots of it is way over my
head, but slowly I am learning. I am
only 70, so I still have some time left
to experiment and learn.
— Morris Sandlin
AI first thought of using the SN74LS292 programmable frequency divider until I discovered that it costs
$14+ each. It would have been
neat because of digital precision
which would eliminate the
possibility of accidentally making
the pulse width greater than the
period (which results in a narrow
pulse instead of a wide one). I
decided to go with a less expensive
circuit (see Figure 2).
I used the CD4060B frequency
divider which has a provision for
a built-in R-C oscillator but it won’t
QI need a variable ratio timer set-up so that as you increase the relay ON time, you automatically reduce
the OFF time. The cycle should
repeat until the timer is turned off. It
needs to be set up using one
potentiometer to adjust the time
periods. The complete cycle is about
one minute and should operate from
a 12-volt DC automobile battery.
I have been successful in setting
up two timers for this purpose, but it
requires adjusting two
potentiometers.
As with a lot of your readers, the
first place I go when a new issue of
Nuts & Volts comes in is “Q & A,”
TIMER PROJECT PARTS LIST
PART
RESISTORS
R6
R7
C1, C3
C2
C4
IC1, IC2
IC3
IC4, IC5
IC6, IC7
VR1
D1
D2
Q1
K1
DESCRIPTION
METAL FILM, 1/4W, 1%, AXIAL
1 MEG POT, 1/8W
TRIMPOT, 20K, 1/8W
.01 μF, 100V, 5%
.1 μF, 100V, 5%
100 μF, 35V, ALUMINIUM
555 TIMER, 8-PIN DIP
DUAL D FLIP-FLOP, CD4013
14 STAGE COUNTER, CD4060
QUAD 2 INPUT NOR, CD4001
22V, 43V@5A
400V, 1A, 1N4004
ZENER, 15V, 1W, DO- 41
NFET, 60V, 300 mA
AUTOMOTIVE RELAY, 12V
■ FIGURE 3
MOUSER PART
271-VALUE-RC
31VC601-F
81-PV37W203C01B00
505-MKP20.01/100/5
505-MKP20.1/100/5
140-XAL35V100-RC
512-LM55CN
595-CD4013BE
595-CD4060BE
595-CD4001BE
650-ROV10-220L-S
512-1N4004
78-1N4744A
512-BS170
653-G8JN1C7TMFRDC12
November 2010 25
