94 Silicon Chip
In the January 1992 issue of SILICON CHIP, you described a “Baby
Room Monitor and FM Transmitter”
based on a BA1404 IC, made by the
Rohm Corporation, Japan. I have
been unable to find any information
on this IC, or the address of the Australian agent.
Could you please help me with the
following questions? Would you have
a data sheet available for this IC? If
not, could you please advise me as to
where I can obtain one, or give me the
address of the Australian agent?
Could you also tell me if it is possible to crystal-lock the IC at radio
frequencies? If so, how can it be done?
(W. W., Beresfield, NSW).
• The Australian distributors for
Rohm Co Ltd are: Fairmont Marketing, 57 St. Hellier Street, Heidelberg
Heights, Vic 3081. Phone (03) 457
7300 or fax (03) 457 7339. They can
supply data on the BA1404 although
we published most of the relevant data
in the October 1989 issue (no longer
available but we can supply photo
copies at the standard $6 fee).
The circuit could be crystal locked
but there is very little point since the
D2
D1
In my model railway control system I am using a number of NE555
timer ICs as switches. Also incorporated is the Traffic Lights Simulator
(again using NE555) and the Points
Controller published in the February
1993 issue. Separately, they work
fine; together, the Points Controller
triggers all others, while the Traffic
Lights Simulator triggers the NE555
switches. I already have 0.1µF capacitors as suppressors on all DC plus AC
power inputs of the modules. Can you
suggest a cure please? (M. W., Surfers
Paradise, Qld).
• When ever there is a problem of false
triggering in 555 circuits, the standard
cure is to install a 0.1µF capacitor in
the positive supply line to the chip
and, more importantly, con
nect a
0.1µF or larger capacitor from pin 5 of
each 555 to the 0V line. This capacitor
is already present in the traffic light
circuit.
Notes & errata
Woofer Stopper, May 1993: unfortunately, the uncorrected wiring diagram
(Fig.2) found its way into the article.
This contains several errors: (1) Q2 is
shown upside down; (2) the 100kΩ
resistor to the right of IC5 should be
deleted; and (3) the 100kΩ resistor
below D2 should be 220Ω. The correct overlay pattern is shown below
as Fig.1. The published PC pattern is
correct.
SC
22k
22k
0.1
220
1000uF
IC1
4060
Q2
IC5
4013
Q6
Q7
1
10M
Q8
33pF
1
Q4
Q1
D3
100k
10uF
0.1
Q5
100k
78L05
IC2
4518
100k
1
33pF
Q3
IC4
4024
IC3
4020
1
1k
Fig.1: corrected
parts overlay
pattern for the
Woofer Stopper.
Mutual interference in
model railway circuits
1k
1k
I have built the Digital Capacitance
Meter as published in the May 1990
of SILICON CHIP. It functions reasonably well, except that it has the
annoying habit of stepping back and
forth around the actual readout; that
is, with the standard 0.1µF capacitor
supplied, the nF scale reads back and
forth from 97 to 102.
I have replaced all the ICs one by one
but still the trouble persists. I would
Questions on the
BA1404
transmitter is very stable, provided
that the specified NPO capacitors are
used.
X1
Fixing jitter in the
capacitance meter
appreciate your assistance to help me
fix this trouble. I enjoy your magazine
and think it is very good value. (D. M.,
North Balwyn, Vic).
• The reason for jitter in the display
is possibly caused by the transformer
not being correctly earthed. Check for
continuity between the transformer
metalwork and ground. You may need
to scrape away the coating on the
mounting feet of the transformer for a
reliable earth contact.
2.2k
trimpot (20kΩ) but it doesn’t seem to
make much, if any, difference. I use
a fairly new Jaycar model QM-1400
digital multimeter to take readings
which should be fairly accurate.
In point of fact, I would like to be
able to bring the cut-off battery voltage
nearer to 1V per cell, which seems to
be a popular figure. The batteries I use
are Optronics OP-3S 6V for a Sony
AU-230 video camera.
The unit as a whole is very satisfactory and easily transported on
a trip but I would like to be able to
reduce the discharge battery voltage
a little lower if possible. (J. L., Big
genden, Qld)
• We are concerned about your difficulty in getting a suffi
ciently low
end-point voltage and while we hesitate to suggest it, wonder about the
accuracy of your digital multimeter.
Check the voltage across the LM3362.5 reference. The tolerance range is
2.39-2.59V and the range of adjustment
with the trimpot is ±70mV. The range
of adjustment can be increased to
±120mV by omitting diodes D1 and
D2 and connecting the trimpot directly
across the LM336.
If your multimeter gives a reading
outside the tolerance range for the
LM336-2.5, we would be inclined to
doubt its accuracy and, by extension,
the accuracy of all your voltage read
ings. If you want to reduce the endpoint voltage of the circuit to 1V per
cell, you will have to recalculate the
voltage divider string across switch
S1.
Note that you can also reduce the
end-point voltage of the circuit simply by omitting protection diode D4.
However, this will mean that you have
no reverse polarity protection for the
circuit and the reduction in end-point
voltage will be proportionately greater
for 12V batteries.
1
22k
D6 D4 D5
