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the base voltage of Q2 when switched
on is about 1V. Note that the 1.5kΩ
resistor between pins 6 and 7 of IC1
will need to be changed to a value
of about 1MΩ to extend the time to
measure this switching when using a
multimeter. Take the coil out of circuit
when doing this since it will draw
excessive current due to the long ontime.
DiscoLight
double triggers
I have a technical query regarding
the DiscoLight which was described
in the August 1988 issue of SILICON
CHIP. I have just built one which works
perfectly in all modes except it triggers
twice on each bass beat. Strobe seems
OK but the ALT and Chaser moves in
two steps and as there are only four
channels only two lights effectively
operate. It triggers fine via the Oscillator. Are there any errata for the trigger
or squaring circuit? Have you heard of
this problem? Any suggestions? (S. S.,
Melbourne, Vic).
• Double beating when used to trigger
from sound is probably caused by there
being too much signal. Try adjusting
the sensitivity down. You may also
find that decreasing the 1MΩ resistor
between pins 8 & 10 of IC1c to 180kΩ
will improve the result. This provides
a much greater hysteresis on Schmitt
trigger IC1c.
Overheating
Tarago
I have been trying to overcome a
long-standing heating problem in my
Tarago van. After checking thermostat
and repairing the radiator, the hoses,
clamps and the head and having the
auto transmission checked, all seems
to be OK. But I still have an unexplained loss of water and elevated
temperature after driving about 100120km. As a result I am forever topping
up the water after every second trip
and can never really have any peace
of mind when travelling.
I want some circuitry to monitor
K-type thermocouples to sense the
temperatures of the automatic fluid
and engine coolant, both leaving and
returning after cooling, as well as the
engine oil and ambient air temperature entering the radiator. I’d like to
display the readings in pairs using
the alphanumeric LCD (May 1993,
Poor gas mileage
in the Kingswood
I installed the programmable
ignition system (March 1996) in
my 1974 Holden HQ approximately four months ago. I though this
would be the solution I was waiting for, to allow me to change my
timing on the fly when changing
from petrol to gas and vice versa.
Overall, I am very impressed
with its operation, and I have noticed a marked increase in power.
But after playing with vari
ous
settings constantly for the last few
months, I am still experiencing
a fairly large drop in my gas fuel
economy. Before installing the system, I could drive from Melbourne
SILICON CHIP) and be able to recall the
maximum reading later.
I feel that by monitoring all the heat
sources simultaneously, I can observe
the thermal runaway building and
catch the offender. I think the trouble
is linked to the way the auto is cooled.
The engine radiator has a small heat
exchanger for the transmission fluid.
It seems that at a particular ambient
air temperature the radiator cannot
handle the load from the auto and this
starts the heating cycle off.
At least, I suspect that this is what is
going on as it appears to occur during
the warmer months of the year. I plan
to transplant the system to a friend’s
4-wheel drive when I have fixed my
problem. I will include the transfer
case and both differentials as he does
some very serious driving. (T. F., Bund
aberg, Qld).
• We have not published any circuits
to suit a K-type thermo
couple and
we do not have any plans to do so in
the near future. However, it may be
possible to modify the Digi-Temp, as
featured in the January 1997 issue of
SILICON CHIP.
As published, this circuit will read
the temperature at up to eight separate
locations at up to 99°C. We have spoken to the designer, Graham Blowes,
and he is confident that it could be
modified to read temperatures to about
120°C. This could make it suitable for
your application.
However, while it is not our normal
to Benalla and back on one tank of
gas, a round trip of approximately
420km. Now, I find that I can only
just make the one way trip. Anyway, I am hoping that someone
can provide me with some suitable
settings to allow for better timing
for gas. Please! The price of gas in
the country is double that of the
city! (R. B., Melbourne, Vic).
• Unfortunately we do not have
any information on ignition timing
for cars and especially not for use
with gas. We can only suggest you
take the car to a speed shop which
has a dynanometer and exhaust gas
analysis equipment. They should
enable you to obtain the best
compromise between power and
economy for your car.
province to give automotive advice,
we think that you have a leak in the
cooling system, not a mechanical
defect which will be revealed by a
temperature monitoring system.
The reasoning is this: if the engine
coolant is overheating and causing the
radiator cap to vent, no fluid should
be lost; it will all go into the overflow
bottle. The fact that you have to top
up the system frequently points to a
leak.
We think that the elevated temperature is caused by the loss of coolant,
not the other way around. We strongly suggest that you take your car to
the local Toyota service people for
a thorough investigation. Leaving it
unrepaired will eventually lead to a
failure of the alloy head and that will
be very expensive to repair.
Notes & Errata
Digi-Temp Digital Thermometer, January 1997: the designer of this project
has advised that the pinout diagram
for the DS1820 sensors is reversed;
the GND terminal should be on the
righthand side and the +5V on the
lefthand side. No damage appears to
occur when this wrong connection
is made.
Smoke Alarm Panel, January 1997:
one of the array of 100µF capacitors
on the circuit of page 29, January 1997
should be 10µF. The component overSC
lays are correct.
April 1997 93
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