Quasar 3126 User Manual
QUASAR CODE # 3126 - SOUND ACTIVATED RELAY SWITCH
General Guidelines for Electronic Kits and Assembled Modules
Thank you for choosing one of our products. Please take some time to carefully read the important
information below concerning use of this product. The assembly and operating instructions are on the
following pages. Help with component identification can be found on our website at
www.quasarelectronics.co.uk/componentid.htm. If you are unsure about any aspect of the assembly or use of
this product please contact our Support Team before proceeding.
WEEE Directive (Waste Electrical and Electronic Equipment)
Notice To All European Union Citizens. Important environmental information
about this product.
The crossed out wheeled bin symbol on this product, package or documentation
indicates that disposal of this product after its lifecycle could harm the environment.
Do not dispose of this product (or batteries if used) as unsorted municipal waste. It
should be disposed by a specialized company for recycling.
The unit should be returned to your distributor or to a local recycling service. Please
respect the local environmental rules. If in doubt contact your local authorities about
waste disposal rules.
Safety: General rules concerning safe use of our Kits or Modules.
To ensure your safety, please observe these safety measures. In no way are these complete. As safety
requirements vary, please check with your local authorities, in order to comply with local requirements.
If in doubt, seek the help of a qualified person.
Battery or wall-adaptor operated devices are safe devices. They do not require special attention unless
mains voltage is connected to an output e.g. a relay.
To ensure electrical safety, and also protection from fire or personal injury, make sure your mains
operated equipment complies with these safety hints:
Use a suitable plastic enclosure. If a metal enclosure is used, make sure it is properly earthed.
Use a power switch if the device consumes more than 10W. Use a double pole switch for mains
operated, transformer-less kits.
Mount a fuse in series with the mains switch. Use a slow blow (T) 50mA fuse for transformers up to
10W and a 100mA fuse for transformers up to 20W.
Use a mains input connector, or a robust power cord with a clamp.
Internal wiring carrying mains voltages must have a minimum cross-sectional area of 0.5mm2.
If supplied, attach the power rating label near the power cord of the device and fill-out the mains voltage,
frequency, power consumption and fuse values.
Troubleshooting and Support
90% of non working kits are due to poor soldering.
We operate a Get-You-Going service for non-working kits but there is a charge based on the time and
components needed to complete the repair. Quite often it is not economically viable for us to repair and it is
cheaper to supply a new ready made product at full cost.
Disclaimer
Quasar Electronics reserves the right to change product specifications or to discontinue products without
notice. Quasar Electronics cannot be held responsible for any loss or damage, direct or indirect, which might
occur from the use of a product. Quasar Electronics Kits or Modules are intended for educational and
demonstration purposes only. They are not intended for use in commercial applications. If they are used in
such applications the purchaser assumes all responsibility for ensuring compliance with all local laws. In
addition, they are not suitable for use as or as a part of life support systems, or systems that might create a
hazardous situation of any kind.
QUASAR CODE # 3126 - SOUND ACTIVATED RELAY SWITCH
The Sound Activated Relay Switch is based on
a circuit published in Silicon Chip magazine,
9/1994, p31. The idea behind a VOX SWITCH
is that instead of the user pressing a switch to
activate a relay, the sound of the users voice
itself activates the relay. This gives hands-free
control over devices like tape recorders.
We have improved the original design by
adding an on-board potentiometer so you can
adjust the trigger sensitivity. The 3126v41
board also features:
1. Screw terminal blocks for all input and
output connections
2. The output is rated to switch up to 120Vac
or 24Vdc @ 1 Amp maximum current. The
relay itself may be rated to switch higher loads
but the PCB tracks limit the amount of current
and voltage that can be safely switched. The
output should NOT be used to switch mains
electricity directly but can instead be used to
switch a higher capacity off-board relay or
switch. The Common (C), Normally
Connected (NC), and Normally Open (NO)
connections are taken to a 3-pole terminal
block on the right hand edge of the board. For
more information please see our relay FAQ
sheet at
www.quasarelectronics.co.uk/pdf/relay-faq.pdf
3. MIC pin spacing increased to make the
MIC body stand off the board. This helps to
reduce a feedback loop that causes the relay to
not turn off (see Note 4 below)
4. “EXT MIC” terminal block input added.
This allows you to mount the supplied
microphone (MIC) away from the board for
convenience or if you are experiencing
feedback that causes the relay to continuously
reactivate or not turn off. Attach using
screened cable no more than 1 metre long. . If
you purchased the pre-assembled version you
will need to carefully unsolder the MIC from
the board first. NOTE: Only use an electret
type MIC as supplied
ASSEMBLY
Check of the components against the Listing.
Follow the overlay for component positions
and orientation. Mount the MIC about 3mm
above board. Note that if the relay is
triggering continuously then it may be
necessary to located the mic some distance
away from the board (like 0.5-1 metre) using
2-core screened cable (not supplied). This
problem is caused by vibration from the relay
itself retriggering the circuit.
Also note that C4 is located under the IC so the
IC socket has to be used. Make sure to get C3
(104) and C4 (101) in their correct places. If
you mix the 101 with the 104 the kit will not
work. Ensure diodes, electrolytic capacitors,
MIC, Q1 and IC1 are inserted with correct
orientation.
COMPONENTS
Resistors 5%, 1/4W:
R1, R7 1K brown black red 2
R3 2K2 red red red 1
R2, R4, R8 10K brown black orange 3
R9 39K orange white orange 1
R5 1M brown black green 1
R6 200K (204) Koa
potentiometer
Capacitors
C4 100pF (101) monoblock 1
C3 0.1uF (104) monoblock 1
C2, C5 2u2 mini electrolytic cap 2
C1 10u mini electrolytic cap 1
Semiconductors
D1, D4 1N4004 2
D2, D3 1N4148 2
Q1 BC548 1
IC1 LM358 1
Miscellaneous
8 pin IC socket 1
RL1 Relay AZ-SH-112L (or
equivalent)
X1, X2 2 pole terminal block 2
X3 3 pole terminal block 1
L1 3mm LED
MIC Electret microphone
PCB # 3126v41 1
OPERATION
Audio is picked up by the microphone and fed
to the opamp IC1a. This is connected as a noninverting amplifier with a gain of 151 or
+43.6dB. The 100pF capacitor across the 150K
feedback resistor rolls off the high frequency
response above 10kHz to eliminate RF. The
output at pin 1 feeds two diodes, D2 and D3
1
1
1
1
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