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Alternative PCB joiner for Linear MIDI Keyboard
Since designing the Linear MIDI
Keyboard (August 2021; siliconchip.
com.au/Article/14997), we realised
there is another way to join the PCBs.
The cut-down pin headers described
in that article are inexact and tricky
to fit, so we designed a small PCB to
make it easier.
We wrote that the pin headers should
be fitted before the switches, but the
Joiners are much easier to work with,
allowing fully assembled Keyboard
PCBs to be joined.
Two of these Joiner PCBs are needed
to join a pair of Keyboard PCBs; this
means a total of 14 Joiner PCBs for a
full 64-note Keyboard.
The Joiner PCBs have a tight solder
mask on one side to stop the solder
spreading and bridging the pads, so
this side should be against the Keyboard PCBs. The side with large solder pads goes on the outside.
Place the Joiner PCB onto the Keyboard PCB. It should line up with
the edges of the silkscreen printing
on the Keyboard PCB. Like any surface mounted part, tack one pad to
correctly locate the Joiner and adjust
as needed.
Unlike the pin header, you can
apply the iron from directly above.
Feed a generous amount of solder into
each pad hole. Surface tension should
pull the solder into the hole and onto
the pad, as long as all surfaces are
parallel and flush against each other.
Gently flip the Keyboard PCBs over
and repeat for the other side using a
second Joiner.
Now test for continuity between
adjacent PCBs. The pads on CON1,
CON3 and CON5 should bell out in
sequence, while those on CON2 and
CON4 will match and also should
connect to different pads on CON6.
If you are unsure, you can also check
the troubleshooting tips at the end of
the MIDI Keyboard article.
Tim Blythman,
Silicon Chip.
Compact reed relay module
Most of the relay modules available
on the internet, although quite inexpensive, are very large due to uncertain
voltage and current requirements. I
needed something smaller, suitable for
use on a breadboard. As many relays
have very short pins, the only option
was to design my own module.
Reed relays are my best option, not
only because of their small size, but also
for their characteristics. Reed relays
have hermetically-sealed contacts, protected against possible oxidation.
They also provide more consistent
switching at low signal levels, requiring less power to operate and with a
better on-resistance.
This is because reed relays use the
magnetic field from the coil to pull sets
of ferromagnetic reed switch contacts
together, which are already in very
close proximity. Thus they do not need
a larger and more complicated armature arrangement.
The relay module has four reed
relays in 4-pin SIL packages along
with SMD driver transistors, hidden
on the underside, plus a set of telltale LED indicators. The driver base
resistors and LED current-limiting
resistors are also SMD parts, keeping
siliconchip.com.au
the module very compact.
The two sets of relay contacts and
the driving connections are each broken out to 4-pin headers, while power
is supplied to the module via a 2-pin
Australia's electronics magazine
header. EAGLE and Gerber files for the
PCB are available from siliconchip.
com.au/Shop/6/6084
Gianni Pallotti,
North Rocks, NSW. ($75)
January 2022 63
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