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Hang problem with
mixture meter
I recently purchased and built
the Digital Fuel Mixture Meter, as
published in the September & October 2000 issues. It has a problem
in which at power-up, it will sit
for a few minutes, reading (L) for
low and no matter what input level
you put into it (0-1V), it will hang.
This problem often goes after two
minutes but may remain in a hang
state for longer.
It is not yet in a vehicle and is
being fed constant 13.5V and a constant input at 0.5V. (F. N., via email).
• This is indeed an unusual problem. It is possibly caused by pin 4 of
Zero voltage switch
for wall oven
Some 15 years ago I redesigned our
kitchen wall oven to something akin to
‘burst firing’ electronic control of the
heating elements. I used a combination
of an Analog Devices AD595 Ther
mocouple Amplifier with a ramp-driven 14-pin CA3059 zero voltage switch
IC to control a suitably-sized Triac. It
has proved to be accurate to ±1° and
quite reliable.
Recently though, the CA3059 failed
and I have not been able to locate a
replacement. Harris and then OnSemi
manufactured them but discontinued
about a year ago. I was wondering if
you could help with the name of a
supplier. (J. N., Tauranga, NZ).
• We do not know of a substitute for a
CA3059 but if you want a zero voltage
switching power control circuit, have
a look at the Heat Controller published
in the July 1998 issue. This used the
IC1 being open circuit, either within
the IC socket or where soldered to
the PC board.
Alternatively, the crystal may be
a slow starter, causing the software
to latch up as it will not be reset
properly. Try using smaller value capacitors from the crystal to
ground at pins 15 and 16. Values
ranging from 10pF to 15pF should
be suitable.
The other problem could be with
the power supply you are using.
If this supply rises slowly to 12V
at switch-on, the circuit could exhibit the problem you experience.
Try connecting the circuit to the
power supply terminals after it is
powered up.
1988 and October/November 1998.
We can supply the 1998 back issues
for $8.80 each, including postage and
the 1988 articles as photostats, again
for $8.80 each, including postage.
Braking system for
a wheelchair
readily available MOC3041 zero voltage switching Triac optocoupler.
We can supply the July 1998 issue
for $10 including airmail postage.
I am a Year 12 student starting my
Major Design Project. My project is a
wheeled walker for the disabled.
My current need is for a braking system and an easier way of going about
it. I want to create a one-off braking
system using electronics and two
motors with a simple on/off sequence
and a button on each handle to easily
apply the brakes.
What do you suggest? (D. G., via
email).
• We suggest you build a speed
control with inbuilt braking. Have a
look at the 50A speed control published in the May 2000 issue. We can
supply this issue for $8.80, including
postage.
Audio frequency power
meter wanted
Notes & Errata
I am in need of an audio frequency
power meter. I’m thinking of something that reads in dB and mV and
takes an electrical input (rather than
including a microphone). It needs to
be accurate across the audio spectrum.
While the option of a microphone
input would be nice, this is a considerably harder proposition, since
the characteristics of the microphone
would have to be compensated for and
accurate calibration would probably
require specialist equipment. (A. M.,
via email).
• We have published two AC milli
voltmeters which would suit your
application, in August/September
RIAA Preamplifier, March 2002: the
10µF across the ±15V rails should be
35V not 16V.
Smart Card PIC Programmer Interface, February 2003: the clock connection from the card socket should
go to pin 12 of the 18-pin socket, not
pin 16.
PortaPAL Portable PA Amplifier,
February and March 2003: there is a
circuit error concerning both the microphone MIC1 and MIC2 inputs. The
circuit shows two 10kΩ resistors in
parallel connecting from pin 2 to
ground whereas one of these resistors
should connect to pin 3 instead. The
SC
PC board is correct.
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92 Silicon Chip
www.siliconchip.com.au
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