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ASK SILICON CHIP
Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line
and we’ll answer your question. Send your email to silicon<at>siliconchip.com.au
Decoding USB Cable
Tester messages
I have just completed the USB
Cable Tester (November & December
2021; siliconchip.com.au/Series/374).
What a great little gadget. I found a
few high-resistance cables, which
I disposed of. The ability to distinguish between power-only vs data
cables allowed me to exercise my
label maker.
However, even after re-reading both
articles again, as well as the June 2021
USB expose, I remain confused about
the meaning of several displayed
messages. I wonder whether you can
explain what these messages mean.
For example, when I plug both ends
of a particular cable in, it is reported
as “POWER ONLY”. On the next line,
the message “CHECK UFP” is present.
But the meaning of that is unclear, and
I am not sure what to do about it.
When the DFP (USB-A) is unplugged,
it now reports what appears to be a
single-ended UFP analysis: “UFP:
DP ,DM ,” What do “DP” and “DM”
mean, and what can be inferred from
the blank field following each? (R. M.,
Ivanhoe, Vic)
● You are correct that the display size
sometimes limits the amount of information that can be displayed, but we
thought we struck a reasonable balance. The DM and DP designation refer
to specific conductors in the USB cable
(also known as D- and D+). These can
be seen in the Fig.1 schematic in the
first article, where they connect to the
various USB sockets.
As noted on page 93 of the second
article, “Check DFP” (or UFP) is a
prompt that you can get more detailed
results by testing one end only. You
appear to have realised this.
The resulting “UFP: DP ,DM ,”
message indicates that the DM and
DP wires of the upstream-facing port
(UFP) are connected together. That
they are not shown elsewhere means
they are not detected at the other end
of the cable.
We didn’t see this type of cable in
108
Silicon Chip
our testing, but it is consistent with
some non-standard cables made for
charging only. The shorted pins are
detected by some chargers or power
supplies to produce a specific charging
current, usually more than 500mA. So
that cable is only suitable for power.
The blank fields simply make the
display more legible by aligning the
listed items.
In general, any DFP or UFP indication apart from GND and SHLD being
connected (in anything but a power-
only cable) is not a good sign. The specifics of that message will only be helpful if you intend to repair the cable.
USB Cable Tester is
only for passive cables
I have built the USB Cable Tester and
have a question about USB-C cables
containing an E-Marker chip. Does the
Tester work with these cables? I have a
USB-C to USB-C cable with a chip in
it, and the Tester tells me it is Power
Only and 0+ 0-. Both ends of the cable
are right-angle connectors, making it
difficult to try all the combinations as
the USB-C sockets are close together.
Thank you for another excellent
project. The SMD Test Tweezers are
useful for SMDs and also through-hole
resistors, with their tiny colour code
bands. (J. B., Blackwood, SA)
● We don’t have many cables with
chips, so we weren’t confident in
advising what the USB Cable Tester
would do when connected to one,
especially as different brands would
probably implement different features.
The Tester only applies a minuscule current, probably not enough to
activate any electronics in the cable.
If power is needed to allow the data
lines to work, they may not be detected
at all, as appears to be the case with
your cable.
Testing USB 2.0
Micro-B cables
Regarding the Micro-B connector
on the USB Cable Tester, I have some
Australia's electronics magazine
equipment that uses the USB 1.1-2.0
Micro-B plug. Will that fit into part of
the USB 3.x Micro-B socket? (A. F.,
Salamander Bay, NSW)
● As far as we know, all USB plugs/
sockets are backwards compatible. The
USB 3.x Micro-B socket is basically a
USB 2.0 Micro-B socket with an extra
socket (with more pins) alongside it.
So you would just plug the USB 1.12.0 Micro-B plug into that portion of
the socket and ignore the rest.
The USB Cable Tester can check
just about any passive cable. The only
thing it can’t do is verify signal integrity for high-speed transfers – that
would be hard to do without making
it much more expensive and complicated.
Finding an amplifier
kit for a beginner
I’ve read your magazine for a long
time, but I’m only at a beginner level
with electronics. I want to build an
amplifier project from your magazine
that I can buy in kit form from Jaycar
or Altronics. Ideally, I would like to
build a stereo amplifier with a bit of
power, but one that is not overly complex to build.
I was thinking of building the Compact 12V 20W Stereo Amplifier (May
2010; siliconchip.com.au/Article/152)
using the Altronics kit, Cat K5136. I
don’t particularly need the 12V option,
but I thought this might be easy enough
to build. Do you have any other recommendations for amplifier kits that
I can buy off the shelf? (E. M., Hawthorn, Vic)
● We agree that this kit is an excellent
amplifier for beginners to build. Most
other kits would involve mains wiring,
whereas this one runs from a safe, low
voltage, but is still very useful. 20W
per channel can be plenty depending
on the speakers and the room.
If you ‘graduate’ to a more experienced level and want to build a
mains-powered amplifier, the recent
Hummingbird miniature power
amplifier is easy to assemble and can
siliconchip.com.au
deliver up to 100W. See the December 2021 issue (siliconchip.com.au/
Article/15126).
SMD Tweezers drawing
too much current
I ordered one of your Christmas
Ornament kits & the SMD Tester Tweezers kit (Cat SC5934, October 2021;
siliconchip.com.au/Article/15057). I
built the Test Tweezers kit first to check
I had the LEDs around the correct way
on the Ornament.
I have noticed that SMD Test Tweezers have a thirst for batteries. When
the display is on, the current draw is
about 6mA, but when it is idle, it only
drops to 3mA! That drains button cells
in just a few hours. I can run it off an
external 3V battery pack with no problems. I built it partly for the novelty,
and to test SMD parts before trying to
solder them in future kits.
Still, it’s a fun testing toy to have.
Thanks for all the hard work selling
these kits. (M. A., Artarmon, NSW)
● That definitely doesn’t sound right.
The expected sleep current is a few
microamps. We’ve built a few prototypes, and they all sit happily idle for
weeks at a time and wake up when
needed, which they wouldn’t do if
they were drawing that much current
all the time.
We suspect that either the OLED
is misbehaving or the micro is not
going to sleep. Check that the display
is completely blank after the five second timeout.
The 6mA drain during use sounds
quite high, so we think something is
continuously drawing an extra 3mA.
That would also explain the high sleep
current. While faulty PICs are rare, we
have come across them occasionally,
so that is possible. But we think more
likely it is the screen, and you should
be able to confirm that by unplugging/
desoldering it.
Spot welder for making
Li-ion batteries
Have you published any articles/
projects on spot welders for making
Li-ion battery packs? (Tom, via email)
● We haven’t, although we will be
publishing one in the near future.
While you can find many designs
for spot welders online. Do not make
one that uses direct mains power –
they are not safe.
siliconchip.com.au
Errors programming
newer PICs
I am trying to convert from the older
PIC series that I am used to, such as
the PIC16F88, to the more modern
(and lower-cost) devices such as the
PIC16F1455, but I have run into a problem trying to program them.
In July 2010, you published an article on using the PICkit 3 to program
micros which I have followed since. In
my setup, I use the PICkit 3 to power
the PIC.
When I went to program the
PIC16F1455, the programming software said that I would have to download new firmware for the programmer,
which it did automatically.
I then followed the standard procedure for programming in the past, and
received a message saying:
PK3Err0045: You must connect to a
target device to use PICkit 3.
PK3Err0035: Failed to get Device ID
I had definitely ticked the box saying power device from PICkit 3. I
repeated the process and received the
same result, this time using a DVM to
confirm that I had 5V on the device.
I changed back to a PIC12F617 that I
programmed before, and received the
same error message. So now I can’t
program at all. I am using MPLAB
IDE V8.91.
Have you come across similar problems and can you help me solve my
problem? (L. K., Ashby, NSW)
● We have run into problems like this,
especially programming newer PICs
with older programmers like the PICkit
3. The PICkit 4 seems to handle this
a bit better (although the PIC16F1455
is supported by the PICkit 3).
We usually use MPLAB X these days
since we need the latest version to
work with the latest parts. We tested
programming a PIC16F1455 using
MPLAB v8.91 (one of the versions just
before they switched to the X series),
and we also couldn’t get it to connect
to or read from the part (although it
updated the programmer firmware as
expected).
Retrying with MPLABX v5.05, it
worked straight away. MPLAB v8.91
is from 2013, and the PIC16F1455 is
about the same age, so it’s a bit of a
‘bleeding edge’ combination (that’s
now about eight years old).
The Microchip Archive has at least
one newer MPLAB version pre-X
Australia's electronics magazine
(v8.92) and all the older MPLABX versions, which you can download from
siliconchip.com.au/link/abcc
We recommend that you try using
a newer version of the IDE. Even if
you insist on using the pre-X IDE for
development, you could still install
MPLAB X and use the programming
software (IPE) that comes with it to
flash the chips.
Universal Dimmer has
limited IR angle
I have been using John Clarke’s Universal Dimmer with Remote Control
since it was published in February
& March 2019 (siliconchip.com.au/
Series/332).
I recently converted a large room
into a home cinema and installed the
dimmer in place of an existing wall
switch beside the screen. The switch
controls four LED lamps and works
fine if not using the remote. But I
find that unless the remote faces the
switch directly (ie, perpendicular to
the touchplate at 5m), it is not recognised, implying a very narrow angle
of sensitivity.
The problem is that it does not
respond at my preferred seating position approximately 6m away from
and 30° to the face of the touchplate.
What, if anything, can be done to
enable me to allow the remote/touchplate combination to work from my
preferred seating? (N. H., Sanctuary
Point, NSW)
● You could use an infrared remote
control extender. This receives and
retransmits the infrared signal from
an infrared LED closer to the receiver
and from a different direction.
Alternatively, use an infraredto-433MHz transceiver. This eliminates the need for a wire between the
receiver and the IR retransmitting LED.
We described such a device in the
January 2022 issue (siliconchip.com.
au/Article/15182).
Sourcing 9mm pots
from overseas
I bought all your parts to make the
3-Way Active Crossover (September
& October 2017; siliconchip.com.
au/Series/318), including the SMD
pack and potentiometers VR3-6.
Now I am having difficulty sourcing
10kW potentiometers VR1, VR2 and
VR7-VR10.
February 2022 109
I am based in Canada, and I don’t
want to order from Jaycar; I would
prefer to find a local distributor. I am
guessing that these are Alpha units.
Do you have the part numbers? (N. M.,
North Saanich, BC, Canada)
● Digi-Key or Mouser should be able
to help you. They are both based in
the USA and have Bourns potentiometers that are equivalent to the Alpha
pots that we used. Search for the following Bourns part numbers on either
website:
PTD902-2015F-A103
10kW dual logarithmic, one required
PTD901-1015K-B103
10kW single linear, one required
PTD902-2015K-B103
10kW dual linear, four required
Inconsistency in SC200
current measurements
I just read the letter from R. S. in the
Ask Silicon Chip section of the October 2021 issue regarding an imbalance in the quiescent current of the
SC200 audio amplifier (January-March
2017; siliconchip.com.au/Series/308).
I was wondering if this was sorted
out because I built four modules and
all had exactly the same difference in
the positive and negative rail. I presumed it was OK as the modules seem
to work fine.
I’ve just purchased the parts to build
two Hummingbird amplifier modules
for my tweeters, and I’ll be following
that with the Three-way active crossovers. Thanks for the great work. (T.
B., Bumberrah, Vic)
● While looking into this enquiry, we
re-read the original letter and discovered a discrepancy. The SC200 articles
state that the safety resistors should be
68W 5W types, but R. S. noted that they
were 6.8W, and we took his word for it.
Now that we think about it, they probably were 68W, meaning the imbalance
was only 5mA, not 50mA.
There is a slight imbalance in the
current drawn by the SC200 amplifier,
on the order a couple of milliamps,
which is swamped by the module’s
quiescent current once the bias has
been set. But before the bias is set, the
difference would be apparent.
The difference has to do with 4mA
flowing from the positive rail to
ground, though the two 6.8kW series
resistors at the collector of Q6, and
the 2mA or so through the 22kW resistor at the collector of Q7 between the
110
Silicon Chip
negative rail and ground. The result is
an imbalance of about 2mA, so the positive rail safety resistor can be expected
to have a voltage drop about 140mV
higher than the other.
We aren’t sure why R. S. noted a
drop of roughly double that, but it
might come down to resistor tolerances, capacitor leakage or something
else we hadn’t considered. As long as
the imbalance equates to just a few
milliamps, the output sits near 0V and
the bias control responds as expected,
we think the amplifier modules should
work fine.
Trouble getting LCD
BackPack to work
I have built your Advanced GPS
Computer kit, but the LCD screen
does not light up. It has 3.3V power
to it. I note in the August 2019 article
on the Micromite LCD BackPack V3
that there is a section on driving the
3.5-inch touchscreen; is this software
incorporated in the pre-programmed
software for the processor?
The LCD Touchscreen still doesn’t
work if I remove the GPS board. I
assume that the V3 Backpack should
work without the GPS board. Without
the GPS board plugged in, I am using
the USB to power the Backpack. The
LCD still does not illuminate.
The only change I made on the GPS
board was because I could not source
the IRLML2244 P-Channel Mosfet. I
have an IRLML2244 on order from RS
Components with delivery due on the
23rd of December, but the date keeps
slipping; I ordered it in August. So I
used an IRF9540N P-channel Mosfet
instead. (J. L., Tauranga, NZ)
● You cannot replace the IRLML2244
with an IRF9540N as it is not a logic-
level Mosfet (it’s also in a totally different package). The -3.3V gate drive
voltage will not be sufficient to switch
it on to any significant extent.
The parts situation is extremely frustrating, but element14 and RS both
have suitable parts in stock, such as the
BSS308PEH6327XTSA1 (element14
Cat 2432719, RS Cat 823-5500).
You mention that the screen has
3.3V power. Where are you measuring this? The LCD panel is only fed 5V
(from the USB socket) and has its own
3.3V regulator. The separate backlight
supply is also 5V. If you have some
photos of your assembled PCBs, that
may help us diagnose further.
Australia's electronics magazine
With the BackPack powered via the
USB socket, a quick way to test the
backlight is to short the two leftmost
pins of VR1 (MANUAL BACKLIGHT)
on the V3 BackPack PCB. You could
solder a jumper header for testing. This
should power the backlight directly,
even if the LCD is not initialised. The
pre-programmed PIC is set up to initialise the LCD, however.
The fact that it is not lighting up
points to a problem somewhere on the
BackPack PCB. Check around Mosfets Q1 and Q2. Q1’s gate should be
at +3.3V due to the pull-up resistor,
while Q2’s gate should be at 0V, being
pulled down by Q1.
Sourcing parts for CDI
project from overseas
Greetings from France. Some time
ago, I purchased components from
you for the Multi-Spark Capacitor Discharge Ignition (CDI) project (December 2014 & January 2015; siliconchip.
com.au/Series/279), including the
PCB, transformer components, ICs,
Mosfets etc.
It’s now wintertime in France, so I
wanted to assemble the kit and purchase the rest of the needed parts
locally.
I’m looking for the S14K275 VAC
metal oxide varistor (Jaycar RN3400,
Altronics R4408), but I can’t find that
exact part here. Same for the Vishay
BCC23922105 100nF class X2 275V
AC capacitor.
Are there any alternatives to these,
or can you suggest where I can purchase them? (P. H., Saint-Pierre-surOrthe, France)
● The S14K275VAC is a metal oxide
varistor (MOV) with the following
specifications:
• Disc diameter: 14mm
• Lead pitch: 7.50mm
• Operating voltage: 275V AC
• Clamping voltage: 710V AC
• Peak current: 4500A
• Maximum energy: 115J
Farnell in France (fr.farnell.com)
sell the EPCOS B72220S0271K101
(catalog code 1004363), which should
be a suitable replacement.
The 100nF 275V AC capacitor is an
X2-rated metallised polypropylene
(MKP) capacitor with a 15mm lead
pitch. Farnell also has an equivalent
to this, the EPCOS B32922C3104M000
(catalog code 1112840).
continued on page 112
siliconchip.com.au
Obsolete parts in older
projects
Could you please tell me whether
any hard-to-get parts are required
to build the Constant High-Current
Source from June 2002 (siliconchip.
com.au/Article/4065) or the 50W DC
Electronic Load from September 2002
(siliconchip.com.au/Article/4029)? I
realise that you probably don’t have
PCBs for these projects. (R. M., Melville, WA)
● For the Constant High-Current
Source from June 2002, the heatsinking arrangements might need to be
changed to suit available heatsinks.
The remaining parts are commonly
available.
For the 50W DC Electronic Load
Advertising Index
Altronics.................................37-40
Dave Thompson........................ 111
Digi-Key Electronics...................... 3
Emona Instruments.................. IBC
Jaycar.............................. IFC,53-60
Keith Rippon Kit Assembly....... 111
LD Electronics........................... 111
LEDsales................................... 111
Microchip Technology.................. 5
Mouser Electronics..................OBC
Ocean Controls............................. 7
PMD Way................................... 111
SC RTV&H on USB...................... 75
SC USB Cable Tester.................. 91
SC Vintage Radio Collection...... 10
Silicon Chip Subscriptions.......... 6
Silicon Chip Shop.................... 101
The Loudspeaker Kit.com............ 9
Tronixlabs.................................. 111
Vintage Radio Repairs.............. 111
Wagner Electronics..................... 87
112
Silicon Chip
from September 2002, the STW34NB20
200V, 34A N-channel Mosfet is obsolete, so an alternative will be required.
Suitable parts that are currently available include the IRFP240PBF, IRFP250(N)PBF, IRFP260(N/M)PBF and
IXTH26P20P.
Searching for another
discontinued part
I am trying to build the Sound
Level Meter from your Electronics
Test Bench book but I am having
difficulty finding a three-position,
two-pole switch with the correct pin
placement. This project is probably
over 20 years old. Is there some way I
can mimic what the switch does with
jumper pins, perhaps? Failing that,
where would I get such a switch? (S.
N., Clayton North, Vic)
● You are right that switches with the
contact arrangement used in that project are no longer available. Switches
are available with a similar layout, but
you will have to wire it to the board
using flying leads. You could use a
DP4T slide switch from Altronics (Cat
S2040) and wire the switch terminals
to the PCB, with the third and fourth
positions wired in parallel.
You could also use the Altronics
S2033 (4P3T) slide switch and ignore
the third pole. It would also be possible to wire up a rotary switch like
Altronics S3008 or S3022, or Jaycar
SR1212.
The PreChamp is an
old design
I am building several PreChamp
pre-amplifiers (July 1994; siliconchip.
com.au/Article/5252) to increase the
signal output from the line output jack
(not the headphone jack) on a TV, and
plugging the resulting increased signal into a Bluetooth transmitter then
to Bluetooth headphones.
It works OK, but I’m not happy with
the resulting audio quality when compared to another pair of wireless headphones that I have.
Using a signal generator and a
Hantek USB scope, I have discovered
that the frequency response of the
PreChamp is not flat. With a constant
input level at all frequencies, I found
that at 100Hz the output level was
85mV but at 10kHz, the output level
climbed to 200mV, and at 15kHz, the
level was 225mV.
Australia's electronics magazine
I have altered the Preamp’s gain by
changing the two resistors to 1500W
and 150W using the formula printed in
the magazine, giving a gain of approximately 11 times, which is around
21dB.
Would this have altered the frequency response of the PreChamp? I
suspect not. Can you suggest any components that I can change the value of
to get the frequency response flatter?
(N. L., Christchurch, NZ)
● The PreChamp is quite an old design
and we would not design something
like that today.
As a result, it has relatively poor
frequency response flatness. Still, it
should not be behaving in the manner
you have described.
Our circuit analysis of the original
design shows that it has a plateau-type
response with -3dB points at around
60Hz and 100kHz, and -1dB points at
around 115Hz and 37kHz. So it suffers a fair bit at the lower frequency
end, but should be pretty flat at the
high end, up to about 20kHz. Changing the gain-setting resistors doesn’t
have much effect on the calculated
response.
Note that we published a new
design in January 2013 – the Champion (and Pre-Champion). That circuit has a much flatter frequency
response. We even published frequency response and distortion
graphs in that article, unlike the original Champ/PreChamp.
Still, we aren’t sure why you are
getting an increased response at
higher frequencies. That points to an
increase in feedback impedance with
frequency, but the only non-resistive
element in the feedback network is the
1.5nF capacitor, which should have
the opposite effect.
The only explanations we can come
up with are that your input coupling
capacitor is too low in value or faulty,
which would cause lower frequencies to have more attenuation and
thus give you a rising response with
frequency. It could also be a similar
problem with the output coupling
capacitor.
SC
The March 2022 issue is due on
sale in newsagents by Monday,
February 28th. Expect postal
delivery of subscription copies in
Australia between February 28th
and March 11th.
siliconchip.com.au
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