guid_volume atenuator and source selection

8/4/2019 Guid_Volume Atenuator and Source Selection

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Volume Attenuator and Selector SourceAssembly and User Guide - v1.0

The Volume Attenuator and Selector Source is a hi-end controller source of volume attenuator

and selectable source of the audio signals.

The selection of volume and/or source selector is provided by the Atmega16 microprocessor.

The complete kit as well as the PCB version may be acquired fromhttp://vicol-audio.ro/

Document version mai 29/2010

The design of this circuit is protected under copyright, 2009-2010. It is available for sell atwww.vicol-audio.ro. It is not

allowed to use (parts of) the design for commercial use without explicit permission of the author.
http://vicol-audio.ro/http://vicol-audio.ro/http://vicol-audio.ro/http://www.vicol-audio.ro/http://www.vicol-audio.ro/http://www.vicol-audio.ro/http://www.vicol-audio.ro/http://vicol-audio.ro/


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Intro

The Volume Attenuator and Source Selector has two versions, R2R and Shunt, of adjusting the

audio signal. The configuration is selected by using three jumpers (J1 communicates with the

microprocessor, J2 and J3 are located on the relay board), followed by a resistance group of a certain valueselected according to the established set mode.

Tests conducted on the two types of volume adjustment options, R2R and Shunt, revealed that the

R2R or Shunt version is superior to any potentiometers commonly found in electronics stores.

The biggest problem is the deviation between the two sections of a stereo potentiometer.

In this design, by measuring the resistance, a lower than 0.1% dispersion can be achieved between the

two audio channels, left and right. Furthermore, by using vacuum sealed relays the operation rate extends

more than twice the average life of a common potentiometer. As a plus, the infrared remote control is a

searched facility by its builders.

Features

Designing the Volume Attenuator and Source Selector comes from repeated attempts of searching for

an optimal variant of microcontroller and memory that can be stored in it, as well as its realization on a

smaller scale.

By using this project any amplifier model can be equipped to compensate for volume control and audio

input selection. The circuit has an IR sensor, model TSOP1736 which allows reception of signals coded


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according to the RC5(Philips) protocol to remotely alter the volume, input source, mute, on/off the amplifier

that it serves.

Any universal remote which also supports the RC5 protocol, may be used. Keys ON/OFF, mute, Ch

(or the 1-4 buttons for direct access to the switched audio sources) and volume from the remote control,

work according to the given circuit.

******************************work in progress*******************************

Remote control configuration, source code, etc.


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The front panel has an Encoder which allows selecting the signal sources volume, 2 buttons,

one for the position ON/OFF source selection and one for adjustment selection, that if it regulates or

adjusts the volume of audio input with the use of the encoder.

Attention: Due to some designing errors, mounting buttons are made as shown above.

The volume attenuator may vary between 0dB-64dB. When using the Shunt option, there are 32

attenuation positions, tuning is sharp, has a higher linearity. R2R has 64 attenuation positions, finer tuning

and a greater logarithmic variation.

The resistances used for the volume attenuator are melf type (higher quality). Optionally you can add

another relay board for the balanced system sources or for obtaining 4, 6, 8 audio inputs. The used relays are

MP-5 or A4W-K (5Vcc coil voltage) with high quality contacts and a very low contact resistance as shown

below.


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This method of volume adjusting is superior to the conventional potentiometer that uses a system of

sliding the cursor on a resistive layer which deteriorates in a relatively short time and causes malfunctions.

Sealed relay contacts maintain their quality for a very long time without inducing parasites in the audio path.

Relay mounting block is recommended to be positioned on the back of the housing to be used, and the

connection is made with a braid//ribbon to the front side where the display block is.

The used models may be found on the site:

http://ro.farnell.com/molex/98267-0277/cable-flat-ffc-12way-152mm/dp/1079970

Ribbon connector on the main board and the relay one.


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The volume control and source selector circuit has been designed to efficiently obtain the signals to be

amplified by power amplifiers.

The project was designed to support another two configurations besides the basic stereo:

-Balancedwhich uses an additional relay board besides the equipped one, in which the relays are

mounted without the power connector, resistance R43( 240ohm), SMD-type LED, voltage stabilizer(

LM1117 or LM7805), bridge rectifier (B800S). One row of long pins are connected between Rel_In

balanced placed on the 2 boards, and a row of long pins (for stability) between the connector P18 from

both relay boards one above the other.


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- 8 stereo inputswhich use 2 relay boards, one fully assembled, the other one mounted on top with

only relays REl7Rel10 and related diodes. On the incomplete board several components wont be added:

the power connector, R43, the SMD type LED diode, U4, B1, Rel1Rel6. A row of long pins are mounted

between Rel_In balanced from both boards but only for pins 1 and 2(ground and +5V) , another row of long

pins (for stability) between the P18 connector from both boards and one row of long pins between the IN1connector from both relay boards( 4 long pins). On the second board (partially assembled one) pins 36

from Rel_In balanced are connected to xCon from the microcontroller board, in order.


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Comments on the schemeControl and Display

The attenuator includes 64 steps for volume setting, created by a series of 62 stages. For each of the 6

relays, each stage presents a contact and 2 resistances (melf model). Each contact has 2 states (NO/NC) so

that for each canal there are 2x2x2x2x2x2=64 volume positions.Resistances were calculated so that each

step is raised or lowered with 1dB.

Viewing can be done on theLCD (2x16 characters) or 2-digit 7-segment:

LCD version. IC4543 and R13R27 (220ohm) are no longer installed, the .hex file is loaded into the

microcontroller for the LCD version. When switching on, the LCD screen will display the software version

of the microcontroller and the programmers name ing. Dan Zup.


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Warning: For the proper functioning of the LCDs backlight, the last two pins must be reversed

between them, as shown in the picture below.


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LED version. The LCD connector is no longer mounted, as well as the adjustable resistance R13,

before powering on; the .hex file is loaded into the microcontroller and set for functioning with the LED

display. When powering on, the volume will be displayed on 2 digits, from 00 to 32-64.

Also, when powering the circuit, the volume minimum level is set for 10 for the R2R version and 7 for

the shunt version.

The S1 button (shown in the picture below) changes the functions of the remote control if you wish

to customize them.

Warning:this option is not present in the 1.0 software version.


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Relays block

The connection to the relay board is made by using a 12-wire ribbon. This buss controls the relays and

supplies the 5Vcc to the microcontroller. Through the RCS connectors, the signal is received and processed

for transmission to the power amplifier.As mentioned above, there are 2 methods of adjusting the volume, R2R and Shunt:

R2R version: red marked resistances are used with J2 and J3 jumpers mounted (resistances

R30LR41L are mounted for the left channel and R30RR41R for the right channel). The jumper

located near the ISP connector (3 pin R2R/Shunt) is switched on the desired mode according to the picture

below.

The ISP connector allows programming the SMD-type microcontroller.


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When exiting the R2R setting, a resistance can be mounted to the GND (in parallel) and experiment for

the volume threshold value for the minimum set value.


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Warning: To take into account the resistances values shown in the picture above, for R2R.

Shunt version: black marked resistances are used, the jumpers J2 and J3 are not mounted(for the left

channel resistances R30L ,R31L ,R33L,R35L , R37L ,R39L ,R41L are mounted with R32L,R34L,

R36L,R38L of 0 ohm, and for the right channel resistances R30R, R31R, R33R, R35R, R37R, R39R,

R41R are mounted with resistances R32R,R34R, R36R,R38R of 0 ohm).

The jumper situated next to the microcontroller switches to the Shunt version, as shown in the above

picture.

For obtaining the 0 ohm value resistances of 0 ohm (SMD type 1206) can be used or a copper wire

strapping the given areas.

Strapping method using a copper wire for obtaining a resistance of 0 ohm.


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Warning: To take into account the resistances values shown in the picture above(left), for the Shunt version.

Audio output may be endowed with a buffer(IC LME49600) for easily leading different interconnected

cables as well as assuring high output impedance.

The circuit provides the buffer through the connector P22situated on the microcontroller board, also

it supplies the necessary voltage, 15Vcc (external power).

This is where the BUFFER goes

The xRel0connectoruses the auxiliary function ON / OFF for the audio power amplifier.

The auxiliary design will be as follows:


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Power source

The Br1 SMD-type represents the bridge rectifier that converts AC voltage to DC voltage. C12 and

C14 provide a supply filter assuring voltage linearization in order of how best to pursue the maximum load

voltage (max. Rs).C13 and C15 filter the high frequency power circuit.

L7805 (LM1117) is a voltage stabilizer of 5Vcc, with a maximum current of 1A.

The minimum AC voltage for stabilization is +2V in comparison to the voltage that needs to be

stabilized, in our case a minimum of 7Vac. The board design supports both the LM1117 capsule and L7805,

mounting can be made on either side of the board depending on the model.


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Given that the wiring has been fitted with a separate ground(GND) for left/right and power/

microcontroller power, resistances R42L and R42R of 0 ohm are not installed when using the audio

amplifiers ground(if the source selector and volume controller share the same premises as that of the audio

power amplifier).


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Solder and connectionsFor a professional soldering we recommend using the hot-air soldering station.

Examples:


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Project in a final stage

Finite boards


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Parts list

Warning: each jumper contains 50 pins.

Components can be bought from:http://www.tme.eu/ro/ or

http://www.vishay.com
http://www.tme.eu/ro/http://www.tme.eu/ro/http://www.tme.eu/ro/http://www.vishay.com/http://www.vishay.com/http://www.vishay.com/http://www.tme.eu/ro/


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Atmel programmer and software

The first step in programming the microcontroller consists in writing the fuse bits:

"Internal oscilator 8Mhz" "Disable JTAG "

continued by writing the program in the microcontroller.

Parallel-port programmer: http://www.embeddedtronics.com/avrprog.html

Schematic


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STK200 compatible 10 Pin programming header port.

Power requirements:

Requires external 5 Volt DC supply. This is usually supplied by the microcontrollers 10 pin programming

header. Any STK200 compatible programming software can be used to program the AVR.

Parts list

AVRprog Revised: Thursday, August 28, 2003AVR STK PROGRAMMER Revision: A

Bill Of Materials August 28,2003

Item Quantity Reference Part PCB Footprint

_____________________________________________________________________

1 1 C15 .1uf =>>AC100\1002 1 D5 IN4007 =>>D400(CA,AN)

3 1 D6 LED =>>LED_14 1 JP25 HEADER 5X2 =>>J\10P

5 1 P3 MALE DB25 =>>DSUB/RP.318/TM/25

6 2 R1,R2 10k =>>7 1 R8 100k =>>R400

8 1 R10 330 =>>R4009 1 U14 74HC244 =>>DIP20


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USB programmer:http://www.fischl.de/usbasp/

Schematic
http://www.fischl.de/usbasp/http://www.fischl.de/usbasp/http://www.fischl.de/usbasp/http://www.fischl.de/usbasp/


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Software

AVRDUDEsupports USBasp since version 5.2.

BASCOM-AVRsupports USBasp since version 1.11.9.6.

Khazama AVR Programmeris a Windows XP/Vista GUI application for USBasp and avrdude.

eXtreme Burner - AVRis a Windows GUI Software for USBasp based USB AVR programmers.

Fuse bit in Bascom

CKSEL = 0100 (CKSEL3 CKSEL2 CKSEL1 CKSEL0)

SUT = 10 ( SUT1 SUT0 )

Significance: 0 is programmed and 1 is unprogrammed .

written by Aureliu Raducu Macovei
http://download.savannah.gnu.org/releases/avrdude/http://download.savannah.gnu.org/releases/avrdude/http://www.mcselec.com/http://www.mcselec.com/http://khazama.com/project/programmer/http://khazama.com/project/programmer/http://extremeelectronics.co.in/avr-tutorials/gui-software-for-usbasp-based-usb-avr-programmers/http://extremeelectronics.co.in/avr-tutorials/gui-software-for-usbasp-based-usb-avr-programmers/http://extremeelectronics.co.in/avr-tutorials/gui-software-for-usbasp-based-usb-avr-programmers/http://khazama.com/project/programmer/http://www.mcselec.com/http://download.savannah.gnu.org/releases/avrdude/

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