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

OPERATION

Audio is picked up by the microphone and fed

to the opamp IC1a. This is connected as a non-

inverting 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

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

QUASAR CODE # 3126 - SOUND ACTIVATED RELAY SWITCH

which function as a half-wave voltage doubler.

These rectify the audio signal to produce a DC

voltage across the 2.2uF ecap, C2 which is

directly proportional to the input audio sound

level.

This DC voltage is fed to pin 5 the second

opamp IC1b. This is connected as a

comparator. A resistive voltage divider applies

about 2V to pin 6. Once the DC voltage across

the 2.2u eCap rises above the voltage at pin 6,

pin 7 pulls high. This turns on transistor Q1

which activates the relay and the LED turns

on. Q1 remains on while the DC voltage at pin

5 is above that at pin 6. Because of the high

opamp gain of IC1a, and with the voltage

doubler gain the circuit has a fast response

time. However, the release time takes about 3

seconds determined by the time constant of

C2, R5 (the 1M resistor) and the pin 6

threshold voltage. D1 across the relay coil

protects Q1 from back-emf when the relay

turns off.

Power the board using a 9-12Vdc battery or for

extended periods a mains adaptor like our

660.446UK. D4 acts as protection for the

circuit in case power is connected the wrong

way. Current drain when off is 5-7mA. It is

about 35mA when activated. Sensitivity may

be varied with the 200K Koa potentiometer. A

good working VOX level is about R6+R9 of

150K. But if you want more sensitivity then

you can reduce R9 to 22K or less and turn the

trimpot R6 to maximum sensitivity (fully

clockwise).

Connect the microphone using 2-core screened

cable up to 1 metre away from the board.

Connect using the EXT MIC terminal block

taking care to observe the MIC polarity (M-

pin goes to the case).

The OFF delay time may be adjusted by

varying R3 and R4. Reducing R3 will result in

a longer release time.

You could change the ON duration (governed

by C2 & R5) to say 30 seconds and use the

VOX as a light switch with this delay time

before turning off. Increase C2 to say 10u and

R5 to 3M3.

support@quasarelectronics.co.uk if you have

any questions.

See our full kit and module range at

www.quasarelectronics.co.uk.

SCHEMATIC

QUASAR CODE # 3126 - SOUND ACTIVATED RELAY SWITCH

Warning! Risk of Electric Shock!

This information concerns kits and modules with relay outputs. TO USE THE RELAY OUTPUTS

SAFELY YOU MUST OBSERVE THE MAXIMUM VOLTAGE AND CURRENT LIMITS QUOTED

IN THE PRODUCT DOCUMENTATION (this is because the board design may not be rated to

switch the maximum voltage and current limits printed on the relay itself or specified in the relay

manufacturer’s data sheet).

Controlling mains equipment with relay outputs must be treated with extreme caution. Electric

shocks can cause severe and permanent injury or even death. Construction, installation, testing and commissioning

should only be attempted by suitably qualified persons, or under the supervision of a suitably qualified person. These

products are not suitable for children. Before connecting mains powered equipment to the relay outputs please check

with the relevant authorities in order to ensure compliance with all current safety regulations.

Many areas of the assembly may operate at mains voltage. A suitable isolating enclosure must be used. Exposed screw

terminal blocks on some products must be insulated to prevent contact with exposed metallic parts at mains potential.

Connected equipment should be suitably fused.

You will find relay outputs on many of the kits and modules that we sell. A relay is an electrically

operated on/off switch. The voltage and current limits specified in the product documentation generally

relate to resistive or light inductive loads.

Relay Terminals

Most boards have SPDT (Single Pole Double Throw) style relays. These have three outputs:

C = Common

NO = Normally-Open contacts connect the circuit when the relay is activated; the circuit

is disconnected when the relay is inactive. It is also called a Form A contact or "make"

contact.

NC = Normally-Closed contacts disconnect the circuit when the relay is activated; the

circuit is connected when the relay is inactive. It is also called a Form B contact or

"break" contact.

Connecting the Device you want to Control

You must provide an external power source to the device you want to control. No voltage

is present at the relay terminals (remember it is just a switch). The relay is normally connected in

series with the positive (+) power wire of the device you want to control.

In this case, the positive wire from the power source should be connected to Common. Then either the

NO or NC terminal (as appropriate for your purpose) is connected to the positive (+) wire going to the

device you want to control. The negative (-) wire does not connect to the relay at all. It goes directly

from the power source negative output to the device negative (-) terminal.

Typical SPDT Relay Connection Diagrams

Anti-Spark SPDT Relay Connection Diagram

Sometimes the connected equipment can cause arcing across the relay contacts. This must be

corrected by installing a resistor and capacitor (not supplied) between the two contacts of the relay as

shown below. Component values are for 230Vac mains.

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