High fidelity reception requires high fidelity
transmission. The TX-AUDIO- 24’s audio frequency
response, dynamic range, separation, signal-to-noise, and
THD numbers match those of the RX-AUDIO- 24.
ASSEMBLING THE WIRELESS GUITAR
■ PHOTO 6. There isn’t much to talk about here as most
of the transmitter complexity and circuitry can be found
on the TX-AUDIO- 24 module proper. This would be a good
time to give you the Digi-Key part numbers for the power
connector (CP202A-ND) and the pushbutton (SW416-ND).
available from Mouser as part number 855-M22-7141042.
USING YOUR NEW WIRELESS
All you really have to do at this point is apply power
to the transmitter and receiver modules. If you leave the
RX-AUDIO- 24 jumper select pins open, you should see
the RX-AUDIO- 24 module’s LINK LED illuminate once
the automatic channel scan completes. Jumper the
TACT_SCAN pin to ground and play with the channel
select buttons on the transmitter and receiver while
observing the LINK LED. Do the same with the CTINU pin
grounded. You’ll be able to see the difference in manually
scanning for a channel button press by button press
and continually scanning for a channel with a single
I tested the audio capability of the wireless guitar
system using a Fender Stratocaster and a Fender Princeton
Reverb amplifier. I powered the TX-AUDIO- 24 and
RX-AUDIO- 24 with identical six-volt battery packs made
up of four AA batteries. The ABACOM radio link worked
as designed and as advertised.
When you download the wireless guitar system
ExpressPCB layout file, you’ll see that I
have mounted the receiver layout on
the same PCB as the transmitter. I’ve
done this to reduce the cost of
obtaining the boards from ExpressPCB.
Instead of having to place two separate
PCB orders, you now only need to
order one board and separate its
receiver and transmitter sections.
Every one of the 11 transmitter
support components are looking at you
in Photo 6. The power supply used by
the TX-AUDIO- 24 is identical to that of
the RX-AUDIO- 24. A couple of high
quality 1.0 µF ceramic capacitors
isolate the TX-AUDIO- 24’s LEFT and
RIGHT inputs. I don’t think you’ll have
any problem assembling this. So,
when you’re done you can mate the
TX-AUDIO- 24 module to its support
PCB as I have done in Photo 7. By
the way, the 20-pin 2 mm socket is
■ PHOTO 7. Again, please note that pin 1
of the TX-AUDIO- 24 is identified with a
silkscreen dot. This time, the pin 1
designator is directly above capacitor C3.
78 May 2009
I’ve presented just one possible
application for the ABACOM RX-AUDIO- 24 and TX-AUDIO- 24 modules.
These units can be used in most any
high-quality wireless audio application.
In addition, you can exploit the
simultaneous audio/data transfer
capability of the modules by adding
a microcontroller to the mix. The USER
_BIT pin can be driven with any microcontroller communications protocol
including RS-232, I2C, and SPI. You may
also invent and send your own protocol
over the USER_BIT digital data link.
Although the RX-AUDIO- 24 and
TX-AUDIO- 24 modules we discussed
did not contain amplifier or ID
selection circuitry, you are now able
to obtain versions of the modules
that do indeed include a headphone
amplifier and active ID selection
circuitry. The TX-AUDIO-24/AE variant
also differs from the TX-AUDIO- 24 in
its reduced power supply voltage
( 3. 3 volts DC), power consumption
( 68 mA), and external quarter wave