E00c050.PDF

GENERAL INTEREST

Sound-to-Light PLUS

Microprocessor-driven lights effects

Design by Ron Wouters

Text by David Daamen

The use of lights effects units in conjunction with music is presently very

popular. Of course we don’t want to stay behind at Elektor. This design

uses a PIC16F84 and has sound-to-light, running lights modes and ‘beat

detection’.

Please note: prototype shown here differs slightly from the PCB layouts shown in Figures 3 and 4.

Most people will remember the running light

units which typically used a 4017, a digital

decade counter whose outputs go high in

turn when a clock signal is applied. And

what about the classic sound-to-light unit:

three lights, each flashing according to the

sounds in different bands of the audio spec-

trum. Those were sound-to-light

units in their most elementary form.

But in the age of the microprocessor

it all has to be faster, better and offer

more functionality. And that is

exactly what this circuit does.

This circuit certainly offers a lot of

functionality, since it combines the

running lights and sound-to-light

modes. The running lights do more

than just go forwards and back-

wards, there is also a choice of sev-

eral pre-programmed patterns. The

unit also has a beat-detection circuit.

Elektor Electronics

12/2000

GENERAL INTEREST

12V

Tr1

B1 = B80C1500

C18

R16

100mAT

IC4

100n

7812

12V

IC1

IC1 = LM324

C19

R15

47k

100n

C29

C27

C25

C23

68n

R14

1000µ 25V

100n

4µ7 63V

100n

BC547B

2x 15V

8VA

R27

C30

C28

C26

C24

10k

1000µ 25V

100n

4µ7 63V

100n

100k

R20

1µ

63V

IC1a

7908

IC5

C20

47k

R18

1k5

R19

47k

100n

R29

680 Ω

1µ5

R17

BC547B

1µ

1N4148

100n

R30

680 Ω

MCLR

RB0

RB1

RB2

RB3

RB4

RB5

RB6

RB7

R31

680 Ω

BF256C

RA4

IC2

1µ

R24

RA3

PIC16

R32

680 Ω

RA2

RA1

RA0

F84

R33

680 Ω

10k

R21

R22

10k

R23

47k

OSC2

OSC1

12V

R28

BC547B

1µ

100n

47k

22k

R26

1N4148

C17

C16

IC3

C13

R10

10k

R11

100k

47p

12V

7805

IC1d

IC1b

X1 = 4.096MHz

1µ

IC1c

1N4148

R34

1N4148

R25

R12

R13

C22

C21

D10

C10

C11

C12

C14

C15

4µ7 63V

100n

2µ2

470n

47n

1µ

BC547B

000107 - 11

Figure 1. The sound processing and control section.

The change of pattern of the running

lights is determined by the beat of

the music. All this can be can be

realised in a simple manner by using

a PIC16F84 to control the lights. This

microcontroller is inexpensive, fast,

has a large number of I/O pins and

can be programmed easily.

causes the lights to step through ﬁve

pre-programmed patterns.

Sometimes the music can have lit-

tle or no beat to it. When the detec-

tion-algorithm cannot find the beat

during six seconds, it causes the unit

to switch automatically to the

sound-to-light mode. In this case,

the unit is also prevented from

switching back to the running lights

mode. The running lights mode will

only be enabled again when the beat

returns.

It’s also possible that no audio

signal is present at all. When this is

the case there is obviously no point

in having the sound-to-light mode

on. When no music is detected for a

period of 30 seconds the unit starts

flashing the lights in a random pat-

tern. Of course the controller will

revert to its normal mode of opera-

tion as soon as the music signal

returns. This way we can guarantee that

some lights effects will always be produced.

And ﬁnally, we can choose to have the unit

work only in the sound-to-light mode.

Circuit

The circuit of the sound-to-light unit consists

of two sections. F igure 1 is the section which

deals with the signal processing and which

provides the signals for the lamp-drivers. The

sound source (for example a CD player or the

REC-out connection of an amplifier) is con-

nected to the circuit via K1. P1 is used to set

the sensitivity of the input. The amplitude of

the signal should be between 0.7 and 1.5 V pp .

After P1 the signal is amplified by IC1a and

T5. This combination of opamp and FET

forms an AGC (automatic gain control) unit

that keeps the signal at a more or less con-

stant level. The values of R5 and C3, which

determine the behaviour of the AGC, have

been chosen such that the beat of the audio

Operation

As we mentioned earlier, the circuit

consists of a running-lights as well

as a sound-to-light unit. The pro-

gram has been implemented such

that the PIC switches between these

two modes every four seconds. In

the sound-to-light mode, the lights

flash to the beat in three bands in

the spectrum of the connected audio

signal. The same audio signal is also

used in the second mode of opera-

tion. Here the beat of the music

12/2000

Elektor Electronics

GENERAL INTEREST

signal is kept intact.

The resulting signal is then fed to three

separate filters: a low pass filter at 160 Hz

(R21, C7, R22 and C8), a band pass ﬁlter set

between 225 and 1060 Hz for the mid fre-

quencies (C5, R17, R18 and C6) and a high

pass ﬁlter at 2340 Hz (C4 and R14). Following

each ﬁlter is an NPN transistor with base and

collector resistors, which converts the signal

to TTL levels. These signals can then

be fed to the PIC for processing.

The signal from the AGC doesn’t

only go to the three filters for the

sound-to-light effect, but also to a

beat-detection circuit. IC1d ampliﬁes

the signal by a factor of 4.7 and is fol-

lowed by a low pass ﬁlter with a roll-

off of 18dB. This filter is designed

with a cut-off frequency of 34 Hz,

using R9, C9, C10, R10, C11, R11 and

C12. The output of the ﬁlter goes to

IC1c, which is the actual beat-detec-

tor. The inverting input of the opamp

is driven by a slightly delayed signal

via C14 and R12, which causes a

series of pulses to appear at its out-

put, with a frequency depending on

the audio signal. If the right type of

signal is present, the output will fol-

low the beat of the music.

These pulses are integrated by D3

and C15 and then go to IC1b. This

opamp is used as a comparator,

where P2 sets the sensitivity of the

beat-detector. The pulses from the

comparator drive T4 via D4 and R25.

This transistor also converts the sig-

nal to TTL levels.

So now there are four signals

available, of which the ﬁrst three are

used in the sound-to-light mode. The

fourth signal determines when the

lights change pattern in the running

lights mode.

The program in IC2 selects the

active mode. A ready programmed

PIC can be ordered from Elektor

Electronics Readers Services (order

code 000107-41 ). For those of you

who wish to program the PIC them-

selves, a diskette is available con-

taining the program (order code

000107-11 ). Please note that the pro-

ject software is not available as a

Free Download from our website

because the author receives royalty

payments on every copy sold of the

disk and programmed PIC.

The processor section is very

simple. The only external compo-

nents used by the PIC are R28, X1,

C16 and C17, which are used to

generate its clock signal. S1 is used

to switch between the fixed sound-

to-light mode or alternating

between the two modes. R27 is

used to keep the signal at the input

12V

IC5

D17

D18

1A T

T HR5

1N5408

CNY65

TIC

106M

R10

D19

D20

12V

IC4

D13

D14

1A T

T HR4

1N5408

CNY65

TIC

106M

D15

D16

12V

IC3

D10

1A T

T HR3

1N5408

CNY65

TIC

106M

D11

D12

12V

IC2

1A T

T HR2

1N5408

CNY65

TIC

106M

12V

IC1

Tr1

1A T

100mA T

IC6

12V

T HR1

1N5408

7812

CNY65

TIC

106M

15V

4VA5

1000µ 25V

100n

4µ7 63V

100n

B1 = B80C1500

000107 - 12

Figure 2. The lamp-driver section.

Elektor Electronics

12/2000

GENERAL INTEREST

of RA4 (pin 3) at a defined level

when the switch is open.

Five outputs of the PIC (RB0-RB4)

are used to drive the lamps. Each

output is connected to K2 via a resis-

tor and LED. These signals are con-

nected to a separate board that

finally drives the lamps. We’ve

designed a separate board since it is

more convenient to place it near the

lamps, or even in the same enclosure

as the lamps. An ordinary low-volt-

age cable (with a minimum of 6

cores) can be used to make the con-

nection.

The lamp-driver board ( Figure 2 )

has an optocoupler (IC1-IC5) for each

channel. In the event of a fault the

control board and any connected

audio equipment will remain isolated

from the deadly mains potential.

When the control board is connected via

K7, the LED in each optocoupler will be con-

nected in series with the LED on the control

board. LEDs D5-D9 will therefore not only

show which lamp should be on, but also that

100mA/T

PIC16F84

Yet again, a microcontroller of the

PIC family from Microchip is used

in this circuit. It’s not surprising

that it is a 16F84. This part is ideal

for design and development work,

because it can be (re)programmed

very easily. There is no need to

erase the device under UV light.

The ﬂash memory is simply over-

written when the device is in its

program mode. Once the design

has been completed, a different

processor can be used for mass

production (for example a cheaper

version without the ﬂash memory).

This is something that we pur-

posely didn’t do. It is always inter-

esting to experiment a little and

this circuit is perfect for that.

There are enough spare inputs left

to use. And you’re not restricted

to switching lamps; many other

mains-powered appliances can be

connected. You could connect a

microphone to the input and use

the high pass ﬁlter and some modi-

ﬁed code to make a whistle detec-

tor to switch appliances on and off.

And there are probably many

other (and more original) applica-

tions. For those who want to ﬁnd

out more about the 16F84 or

other Microchip processors, their

website is at www.microchip.com .

On www.thepicarchive.cwc.net

you’ll ﬁnd a wide range of PIC-pro-

grammers, programming software,

program examples and projects.

There are also descriptions of ‘in-

circuit’ programmers, so you no

longer have to remove the PIC

from the circuit in order to pro-

gram it.

C18

R10

C13

R11

R12

R25

R14

R15

R22

R23

R19

R17

R18

R33

R32

R31

R30

R29

R16

R20

R27

C20

Figure 3. Copper track and component layout of the control PCB.

12/2000

Elektor Electronics

GENERAL INTEREST

100mA/T

1A/T

IC1

1A/T

IC2

D12

D11

D10

1A/T

IC3

D16

D15

D14

D13

1A/T

IC4

D20

D19

D18

D17

1A/T

IC5

Elektor Electronics

12/2000

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