wireless audio station

WIRELESS AUDIO STATION

FINAL REPORT

SENIOR DESIGN GROUP 246

ZAINAB SANUSIJOHN CHRISTENSEN

DIPTESH PATEL

TABLE OF CONTENTS

1.) Background…………………………………………………………………...3

2.) Requirements………………………………………………………………….4

3.) Block Diagrams……………………………………………………………….5

4.) Design Implementation Methods……………………………………………...9A.) Main Control Unit…………………………………………………….9B.) Dual Receiver Relay Board………………………………………….11C.) Packaging…………………………………………………………….11

5.) Schematics……………………………………………………………………12

6.) Technician’s Troubleshooting ……………………………………………….13

7.) Lessons Learned……………………………………………………………...14

8.) Appendix……………………………………………………………………...15A.) PCB Layout…………………………………………………………..15B.) Budget………………………………………………………………...16C.) Software Code………………………………………………………...17

Final Report: Group 246 2

Background:

The goal of this project was to take a cost effective wireless microphone system and add enhancing features which would normally only be found on very expensive high-end wireless systems. Then combine them into a portable easy to use package that provides quick setup and takedown times. The features that were added are as follows:

1.) Auto Channel Selection. System scans its 16 available frequency channels for interference and selects the best three for use.

2.) LCD Display3.) Convenient carrying case with system base station integrated into it for very fast

setup and takedown times

The system will be used during the ECE departmental meetings to supply high quality wireless audio from the speaker and the audience to a video camera and the PA (public address) system.

The graphic below illustrates how the wireless audio station will be used.

Figure 1: Operation Illustration


The person speaking will use a wireless lapel microphone and there will be a wireless handheld microphone in the audience. Both will send audio to the wireless audio station. Once sent, the audio will be sent through a mixer and then sent to a video camera which will be recording the meeting and also to a transmitter which will send the mixed audio wirelessly to the PA(public address) system.

Requirements:

The requirements of our project are as follows:

The collection site needs to be capable of receiving at least two sources.

Each audio source needs to be able to attach to an appropriate transmitter.

At least some of the transmitters need to be able to conveniently attach to something like a lapel microphone.

The transmitters need to be able to operate without causing interference to one another.

The transmitters connected to the audio sources need to be battery operated and should provide some indication of battery condition.

Transmission range must be reliable and noise-free up to 70 feet.

The frequencies used for the wireless ‘links’ should be flexible/changeable, should there be interference on the default frequencies

The transmitters need to meet FCC guidelines.

The audio at the collection site needs to be in an appropriate form so that it can be routed (under adjustable gain) to a recording device or to the input of other audio-type equipment such as a mixer.

The system should be easy to set up and take down because of time limitations.

The collection site needs to be able to selectively transmit any of the received audio sources or an external audio source to an auxiliary sound system.


Block diagrams:

During the beginning phases of our project we had three different design options to consider before we finally settled for the design below. One of the options involved more equipment than was necessary and one design option was determined to be not possible without running into interference problems. This left us with the design shown in the following block diagram. This option was also good because it was economical and required the least amount of setup.

Fig.2: Entire system block diagram. Un-bolded devices were provided, and bolded devices were obtained or produced as part of the project. (The dotted lines indicate wireless connections).

Final Report: Group 246

Mic 1

Transmitter 1

Receiver 1

Mic 2

Transmitter 2

Receiver 2

Audio Mixer

Recording Device PA Transmitter

Receiver 3

SpeakerSystem

Main Control Unit

Interference Detecting Receiver

5

The following flow chart in figure 3 is for just the main control unit.

Fig. 3: Main Control Unit Block Diagram


Interference Detecting Receiver

Sallen-Key Active Filter 2nd Order Low Pass Filter Cutoff Freq. = 1Hz, Gain=1

PIC 16F877A LCD SCREEN

UF2064 Receiver

UX16 Transmitter

16-Bit Shift Reg. Serial to Parallel

10 Reed Relays

Bilateral Switch IC

Bilateral Switch IC

6

Shown below in figure 4 is a flow chart for the scanning portion of the software.

Fig 4: Scanning Software Flowchart


Start

i =0

i < 16

Increment i

Read A2D

Save A2D read

Compare all 16 channels

Select lowest 3 channels

Set receiver1 & 2 and Transmitter 3 to selected channels

Display selected channels on LCD

Stop

No

Yes

7

Receiver 1, receiver 2 (receiver 1 and 2 are part of a dual receiver box), the interference detecting receiver, the PA transmitter, the mixer, and the main control unit were all placed together in a convenient and portable package. For this project all of the devices were packaged into a medium size duffle bag. All together, the devices and bag make up the wireless audio station. The wireless audio station is shown below in the following pictures.

Ready for Transport

Ready for Operation


Design Implementation:

The project design implementation can be divided into four main sections:1.) Main Control Unit2.) Dual Receiver Relay Board3.) Packaging

A.) Main Control Unit

Figure 5: Main Control Unit

The main control unit is the heart of the project, or brain if you prefer. It contains the microprocessor and other IC (Integrated Circuit) chips used to control the wireless audio station. The main board’s purpose is to control the channels of the dual receiver, the interference detecting receiver, and the PA transmitter. It has the ability to accomplish this in several different ways. It has the ability to scan through all sixteen available channels, select the best three, and set them to the dual receiver and the PA transmitter. Also, it has a manual mode feature which allows the channels of the dual receiver and PA transmitter to be selected manually by the user. For user convenience the main control unit sets the interference detecting receiver, the dual receiver, and the PA transmitter to the same four channels every time it starts up. This reduces setup time if interference is known not to be a problem.

Inside the main control unit lies a PIC16F77A microcontroller, two quad bilateral switch IC’s, an op-amp, and a 3V DC (Direct Current) voltage regulator for powering the PA transmitter without the need for two AA batteries. The bilateral switch IC’s are used as an electronic replacement for the original 4 DIP switches used to set channels on the


interference detecting receiver and the PA transmitter. The op-amp is set up in an active Sallen-Key 2nd order low pass filter configuration.The main control unit receives a DC signal from an IC chip inside of the interference detecting receiver that was identified as an “FM (Frequency Modulation) IF (Intermediate Frequency) System”. This IC chip is listed as having several abilities included quadrature detection which can be used to demodulate FM signals. This chip has a “signal power” output that ranges from 0-5 volts depending on received signal strength. This “signal power” output serves as the input to the main control unit. Once inside the main control unit this input signal goes through the low pass filter to filter out noise and achieve a cleaner DC signal which is then sent into the PIC16F877A A/D converter.

During scanning mode the main control unit goes through all 16 of the interference detecting receiver’s channels, taking an A/D reading for each, comparing, and setting the dual receiver and PA transmitter to the channels with the lowest A/D reading.

Figure 6 below shows the PIC16F877 pin connections.

Figure 6: PIC16F877 Pin Connections


B.) Dual Receiver Relay Board

The dual receiver has the ability to be set to sixty-four different channels but in order to work with the other sixteen channel equipment only the sixteen common frequencies are used by the wireless audio station. Having more channel options means that there is more manual switches to replace with switches that can be controlled by the PIC16F877A. A second PCB was made to be placed inside of the dual receiver enclosure. This PCB contains a 16-bit serial in parallel out shift register and ten 5V mechanical reed relays. The shift register allows the PIC16F877A to expand its output ports and the reed relays are used to replace the manual mechanical switches that originally controlled the dual receiver channels. The shift register outputs 1-10 control the 10 relays.

C.) Packaging

The bulk of the packaging work was the process of constructing the internal frame for the wireless audio station duffle bag. The material used for construction was sheets of five eighths inch black plastic and quarter inch white plastic. All frame pieces were machined using a mill to achieve great precision.

The main control unit is housed inside of a 4.88”x6.88”x1.5” enclosure made of black ABS plastic. The holes for the LCD screen, buttons, and connectors were also made using a mill to achieve great precision.

Connecting cables were made using CAT-5 networking cable. The connectors used on the connection cables were 8-pin mini DIN connectors.

The DC power supplies for the devices within the wireless audio station are all plugged into an AC power strip that was mounted in the left pouch of the audio station as shown below in figure 7.

Figure 7: Wireless Audio Station Power Supplies


Schematics:

Shown below is the schematic for the main control unit PCB.

J1

HDR1X14

J2

HDR1X7

J3

HDR1X2

J4

HDR1X6

J5

HDR1X5

J6

HDR1X5

U3

741

3

2

4

7

6

5 1R1

1.0k

R2

1.0k

R31.0k

R4

1.0k

C11.0uF

C2

1.0uF

U4DIP14Quad Bilateral Sw itch

2345 17

14119 1210

6

138U5DIP14

Quad Bilateral Sw itch

2345 17

14119 1210

6

138U28DIP28

PIC16F877A

2

19

3

16

4

17

5

20

1

18

714 811 912 10 613

21 22 23 24 25 26 27 2815

U1DIP12

2345 1

8 119 1210

67

R5

100R6

1.0k

R7

100R8

100 R9

100

R10

1.0kR11

1.0k R12

1.0k

J8TEST_PT1Signal Input

J7

HDR1X5Voltage Regulator

C3

1.0uF

X1HC-49/U_1.5MHz

C4

22pF

C5

22pF

Fig 8: Main Control Unit PCB Schematic

The following figure 9 shows the schematic for the dual receiver relay board. The socket in the upper left of the schematic is for the shift register and the other sockets are for the ten reed relays and the input/output wires.


U1

DIP14

2345

1

7

14

11

9

12

106

13

8

U2

DIP14

2345

1

7

14

11

9

12

106

13

8

U3

DIP14

2345

1

7

14

11

9

12

106

13

8

U4

DIP14

2345

1

7

14

11

9

12

106

13

8

U5

DIP14

2345

1

7

14

11

9

12

106

13

8

U6

DIP14

2345

1

7

14

11

9

12

106

13

8

U7

DIP14

2345

1

7

14

11

9

12

106

13

8

U8

DIP14

2345

1

7

14

11

9

12

106

13

8

U9

DIP14

2345

1

7

14

11

9

12

106

13

8

U10

DIP14

2345

1

7

14

11

9

12

106

13

8

U11

DIP24

2

19

3

16

4

17

5 20

1

187

14

8

11

9

12

10 15

6

21222324

13

U12

DIP6

23 4

51 6 U13

DIP10

2345

1

78910

6

Fig 9: Dual Receiver Relay PCB Schematic

Technicians Troubleshooting

Problem – No audio is heardWhat to do – Check all cable connections to make sure they are making contact. Check power lights on receivers to make sure that they are on and units are receiving power. Make sure that audio mixer battery is not dead. Check status light on receivers to make sure that they are receiving the microphone signal. If status light is not turning on double check to make sure the transmitter and receiver are on the same channel. Make sure transmitter batteries are charged.

Problem – Audio is distortingWhat to do – Make sure that receiver gain knobs are set to the 1 o’clock position and the mixer gains are set at one eighth and then adjust the PA transmitter gain until distortion is gone.

Problem – No matter how wireless audio station gains are set the microphones do not get loud enough.What to do – Turning up the gain on the microphone transmitters should solve this problem


Note: For microphone specific problems see the Gemini UX-16 and Gemini UF-64 manuals that came with the wireless microphone systems.

Project Comments

Throughout the designing and building process there were several important problems encountered and corresponding lessons learned from them. The following is a list of these problems and the lessons that were learned.

Quad bilateral switches worked with sixteen channel units but not with sixty-four channel unit. After building our secondary dual receiver PCB using bilateral switches we discovered that the bilateral switches would not work because they do not make a perfect closed connection and they do not make a perfect open connection. The bilateral switches were later replaced with the mechanical reed relays.Lesson Learned – Test, test, test, before building. Much time can be saved that way. Even if it seems like the test is not necessary it should probably be done anyway.

The original design involved taking a high frequency signal from the interference detecting receiver and amplifying it on the main control unit PCB. Our original main control unit PCB did not have a ground plane and there was a fair amount of “cross talk”.Lesson Learned – Always use a ground plane when high frequencies are in play

A lot of constructive criticism and ideas were received during faculty review day. After which we discovered that we did not need to be manipulating the high frequency intermediate frequency signal from the interference detecting receiver. It turned out that a chip in the interference detecting receiver had a received signal strength output which already ranged from our desired voltage.Lesson Learned – Be careful to consider all design options and look for shortcuts that may have been missed.


Appendix:

1. PCB Layout

Fig 10: Main control unit PCB layout

Fig 11: Relay switches PCB layout


2. Budget

The items below are the items we had paid for:

Qty Part Name Unit Price ($) Total Price($)2 UX-16L Wireless Mic System 89.99 179.981 UF-2064ML Wireless Mic System 219.99 219.991 16-bit Shift Register (digikey-74F675APC-ND) 9.66 9.668 Bilateral Switch IC(s) .50 4.001 Plastic Enclosure Box 9.73 9.731 Power Supply 12.95 12.951 5-pin DIN Female Panel Mnt. 1.35 1.353 8-pin Mini DIN Female Panel Mnt 1.53 4.593 8-pin mini DIN Male In-Line connectors 1.32 3.961 3-VDC Voltage Regulator 2.14 2.14

Total 448.36

The items in the table are the items we got for free from Bart and from ourselves:

Qty Part Name Unit Price($) Total Price($)1 20 x 4 LCD Display 29.17 29.172 PIC 16F877 9.68 19.362 LT5537 Chips 4.20 8.402 Chip Holders 3.98 7.9612 Resistors 0.42 5.045 Capacitors 0.45 2.251 20MHz Crystal 2.78 2.782 PCB Boards 20.00 20.004 Normally Open Momentary Buttons 1.25 5.00

Total 99.96


3. Software Code

// --- wireless audio-------------------// // SENIOR DESIGN GROUP 246// MEMBERS:// ZAINAB SANUSI// JOHN CHRISTENSEN// DIPTESH PATEL// // This program reads the RF power detected by the RF Detector from the // 16 channels of our scanning receiver,compares all the 16 channels and selects // the lowest three of the RF power read,then sets the PA transmitter, and the // dual receiver to these channels////// I/O connections:// RA0 = analog A/D input read// RC0..RC3 = outputs 0/1 to change channels on RF Interference Receiver// RD0..RD3 = outputs 0/1 to set the PA Transmitters channels// RE0..RE2 = outputs 0/1 to the shifts registers for the dual receivers////--------------------------------// Revision History// 1/30/2006: Starting program (ZYS).// 4/10/2006: Added subroutine to change channel on RF interference receiver.// 4/18/2003: changed all output and input pins due to change of PIC from // PIC 16F7876 to 16F7877. More output pins were needed to and PORTA// can only supply so much,so we needed PORTS D and E on a bigger PIC.////------------------------------

// Global Variablesunsigned int Data1; unsigned int Data2; unsigned int Data3; #define NUM_CHANNELS 16#define NUM_MIN 3

// Subroutine Declarations#include "a2d.h"#include <pic.h>#include <string.h>#include "lcd_20x4.h"


#include "function.h"#include <math.h>

// Subroutines#include "a2d.c"#include "lcd_20x4.c"#include "lcd_msg.c"#include "function.c"#include "bootloader.c"

void Timer2_Init(void){ T2CON = 0x47; // 10ms interrupt rate PR2 = 100; TMR2IE = 1; PEIE = 1; TMR2ON = 1;}

//---------- this is the A2D subroutine----------

void a2d_Init(void){ ADCON0 = 0x81; TRISA = 0x01; ADCON1 = 0xB4; }

unsigned int a2d_Read(unsigned char c){ unsigned int result; c = c & 7; ADCON0 = (c << 3) + 0x81; ADCON0 += 4; do {} while ((ADCON0 & 4) > 0); result = (ADRESH << 8) + ADRESL; return(result);}

//------------this is the LCD message subroutine-----

void lcd_msg(void){


unsigned char A[20];unsigned char i;

lcd_move(0,0);strcpy(A, "SET DEVICE CHANNELS");for (i=0; i<19; i++) lcd_write(A[i]);

lcd_move(1,0);strcpy(A, "LAPEL MIC: CH");for (i=0; i<13; i++) lcd_write(A[i]);

//lcd_move(1,14);//strcpy(A, "CH");//for (i=0; i<2; i++) lcd_write(A[i]);

lcd_move(2,0);strcpy(A, "HANDHELD MIC: CH");for (i=0; i<16; i++) lcd_write(A[i]);

//lcd_move(2,17);//strcpy(A, "CH");//for (i=0; i<2; i++) lcd_write(A[i]);

lcd_move(3,0); lcd_write('P'); lcd_write('A'); lcd_write(' '); lcd_write('R'); lcd_write('E'); lcd_write('C'); lcd_write('E'); lcd_write('I'); lcd_write('V'); lcd_write('E'); lcd_write('R'); lcd_write(':');

lcd_write(' '); lcd_write('C');

lcd_write('H');

}

//-----------functions subroutines-----------


// Generally useful functions//// void hex2dec(unsigned int X, unsigned char *A[5])// separate an unsigned integer into decimal// A[4] * 10E4// A[3] * 10E3// A[0] * 1//// void Wait_ms(unsighed int X)// wait approximately X milliseconds and return

void hex2dec(unsigned int X, unsigned char *A[5]){ unsigned int Y; unsigned char a4, a3, a2, a1, a0;

a4 = X / 10000; Y = a4; X -= 10000 * Y;

a3 = X / 1000; Y = a3; X -= 1000 * Y;

a2 = X / 100; Y = a2; X -= 100 * Y;

a1 = X / 10; Y = a1; X -= 10 * Y;

a0 = X; A[4] = a4; A[3] = a3; A[2] = a2; A[1] = a1; A[0] = a0; }

// ---- WAIT_MS ----------------

void Wait_ms(unsigned int X){ unsigned int Y;


do { Y = 500; do { Y -= 1; } while (Y > 0); X -= 1; } while (X > 0); }

// - ASCII ------------------------

unsigned char ascii(unsigned char c) { c = c & 0x0F; if (c < 10) return (c+48); else return(c + 55);}

void Display_Data(unsigned int Data) { lcd_write('0'); }

unsigned char switch_channel(int channel){

PORTC = ((PORTC &0xC3) | (channel <<2));

}

// Main Routine

void main(void){

unsigned int a2d;int channel[NUM_CHANNELS];int minimum[3];int i = 0;int j = 0;int k = 0;char min;


TRISC = 0xC3; // make init routine and put it in there TBD

a2d_Init();lcd_init(); // initialize the LCD

Wait_ms(1000); lcd_msg();

Timer2_Init(); // initialize Timer2 for 10ms

do{

for (i = 0; i < NUM_CHANNELS; i++){

switch_channel(i);Wait_ms(10000);channel[i] = a2d_Read(0);

}

do{

for (k = 0; k < NUM_MIN; k++){

minimum[k] = 0;min = channel[0];for (i = 0; i < NUM_CHANNELS; i++){

skip = 0;for (j = 0; j < k; j++){

if (i == minimum[j]){

skip = 1;break;

}}

if (skip != 1 && channel[i] < min){

min = channel[i];minimum[k] = i;

}}

}


Data1 = minimum[0];Data2 = minimum[1];Data3 = minimum[2];

lcd_move(1,13); lcd_write(ascii(Data1));



} while(1>0); }


wireless audio station

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