Advertising Index
Altronics.................................35-42
Control Devices........................... 51
Dave Thompson........................ 111
Digi-Key Electronics...................... 3
ElectroneX................................... 17
element14................................OBC
Emona Instruments.................. IBC
Hare & Forbes............................. 47
Icom Australia............................. 13
Jaycar.................IFC, 11, 15, 18-19,
................................... 93, 95, 97, 99
Keith Rippon Kit Assembly....... 111
Lazer Security........................... 111
LD Electronics........................... 111
LEACH PCB Assembly................ 55
LEDsales................................... 111
Mastercut Technologies............. 16
Microchip Technology............ 7, 71
Mouser Electronics....................... 4
Oatley Electronics..................... 111
Rohde & Schwarz.......................... 9
SC Raspberry Pi Pico W............. 46
Silicon Chip Shop............ 106-107
Silicon Chip Subscriptions........ 72
Silicon Chip Test Tweezers..... 109
The Loudspeaker Kit.com.......... 12
Tronixlabs.................................. 111
Wagner Electronics....................... 8
Errata and Next Issue _____________
Active Mains Soft Starter, February & March 2023: the right-hand
column on page 71 of the March
issue says to use red or black wire
for Active. It should have said red
or brown.
Next Issue: the June 2023 issue is
due on sale in newsagents by Monday, May 29th. Expect postal delivery
of subscription copies in Australia
between May 26th and June 12th.
112
Silicon Chip
unit is similar to ours, a reading of 84
ADC steps corresponds to 0A, with
21 more steps per additional amp; ie,
105 means 1A, 126 means 2A, 147
means 3A etc.
We recommend adding a line
“Serial.println(p);” to the main sketch
loop() function; p is the sampled current sense analog value. This will
allow you to quickly check the calibration of your unit as you apply test
loads and possibly increase the current
limit with safety.
A simple fix might be to use a single-
diode rectifier, which should reduce
the inrush current by half. If the load
on the converter is relatively low, a
series resistor might work to limit the
inrush current at the cost of dissipation in the resistor. An NTC thermistor rated at a few amps would be even
better but more expensive.
Since the DCC signal is an AC
source, you could also use a capacitor
(in series) dropper. Simulations suggest that values around 100nF to 1µF
in one of the AC legs from the DCC
signal (ie, before the bridge) might be
in the workable range for the 220µF
capacitor on the XC4514 buck converter. Still, it will depend on the load
on your buck converter.
Choosing a transformer
for the Class-A amp
The Altronics transformer specified for the 20W Class-A Amplifier
(May-September 2007; siliconchip.au/
Series/58) is listed as 16-0-16V AC. I
have an 18-0-18V AC transformer on
hand. Is it OK to use this? If so, would
I need to change any circuit values? (R.
H., Berowra Heights, NSW)
● An 18-0-18V transformer would
result in a higher DC voltage than the
amplifier is designed for, and it isn’t
easy to change it to handle that. You
can use your transformer if you backwind the secondaries until you get an
output closer to 16V AC for each. If
you can’t get the 16-0-16 transformer,
a 15-0-15 transformer might be available and would only reduce the output power slightly.
Fixing the Automatic
Rain Gauge
Many years ago (in 2000), I built
your tipping bucket rain gauge (June
2000; siliconchip.au/Article/4325),
and it has been working without fail
Australia's electronics magazine
until recently. Now it wouldn’t record
rainfall. I have diagnosed the fault to be
the IR sensor in the bucket assembly.
Not having the original documentation that came with it, I am stuck
as to what the part is, but I have a
bucket assembly from a failed Bunnings wireless unit. This bucket uses
a reed switch and magnet. Would it
be possible to get a copy of the circuit
diagram so I can investigate if it’s possible to use a reed switch assembly?
(C. L., Allingham, Qld)
● The sensor used in the Rain Gauge
was the Jaycar Z1901 photo interruptor, which is still available. We still
have plenty of June 2000 back issues
if you need the circuit diagram, or
you can get online access, via the following links: Print: siliconchip.au/
Shop/2/319; Digital: siliconchip.au/
Shop/12/3138
Replacing the sensor with a reed
switch is easily possible. Just connect
the reed switch between pin 6 of IC1
and circuit ground. That is the same
connections as for the photo interruptor phototransistor collector (pin 6)
and emitter (GND).
If the bucket assembly from the Bunnings wireless unit tips the bucket
each time it collects 1mm of rain, it
should work with the Rain Gauge. Our
Rain Gauge had an 86mm diameter
collection area, so the volume of water
collected for 1mm of rain is 5.808cm3
or 5.808mL (π × 43mm2 × 1mm).
Optocoupler transistor
base connection
What do you connect the phototransistor base to when using an optocoupler like the 4N25, 4N26, 4N27
or 4N28? Leave it open, connect it to
ground? (F. C., Maroubra, NSW)
● Generally, the base is left open. A
resistor can be added between the base
and the emitter to speed up the output response. This allows the transistor to switch off faster in the absence
of light. However, it also reduces the
sensitivity of the optocoupler, so more
input current is required to switch on
the output transistor. Care should be
taken not to exceed the LED’s current
ratings.
When using a base resistor, its value
is a compromise between output
switch-off speed and input sensitivity.
10kW could be a good starting point.
For more information, visit:
siliconchip.au/link/abl5
SC
siliconchip.com.au
