e013026.PDF

GENERAL INTEREST

MIDI Lights

& Slide Control

controlling slide projectors with MIDI commands

Design by A. Mylle

In the January 2001 issue we showed that it was possible to control other

things with MIDI besides the usual musical instruments. This time, MIDI

signals are used to control light sources. There are four adjustable triac

outputs and eight relays to control, for instance, four slide projectors.

Elektor Electronics

3/2001

GENERAL INTEREST

Table 1. Types of MIDI-messages.

channel voice

channel mode

system common

system realtime

system exclusive

messages

note off

all sound off

midi timecode quarter frame

timing clock

system exclusive

note on

reset all controllers

song position pointer

start

sample dump

poly pressure

local control

song select

continue

device inquiry

control change

all notes off

tune request

stop

ﬁle dump

program change

omni off

eox (end of exclusive)

active sensing

…

channel pressure

omni on

system reset

midi show control

pitch bend

mono on (poly off)

midi machine control

poly on (mono off)

…

When controlling lights, it is not easy

to maintain synchronisation

between light and sound when the

control signals reside on different

media. There exist a plethora of pro-

fessional equipment that make syn-

chronisation possible, but usually

have a price tag attached that is well

beyond the means of the amateur.

Cheaper systems may have limited

expandability and often cannot be

interconnected with systems from a

different brand.

Hence the idea to control (slide)

projectors and relays via MIDI,

where ‘light events’ can be manipu-

lated with a MIDI/audio-sequencer.

Synchronisation is no longer an

issue, since everything is now con-

trolled from a PC. By using MIDI as

the medium, the application of the

MIDI lights is now independent from

any hardware or software. If you

have at your disposal a MIDI-

sequencer with audio capabilities,

then it is possible to mix the sam-

pled audio with MIDI. And, if this

sequencer possesses more than one

separate MIDI-output, then it

becomes possible to connect multi-

ple light controllers.

as the MIDI-music then congestion on the

MIDI-cable is guaranteed to arise.

More important then the load on the MIDI-

cable is the problem that sysex-messages are

not normally displayed in graphical form on a

sequencer. There will, at best, be a list of

hexadecimal numbers in the play list. To edit

light events with the music is virtually impos-

sible. There is, however, another possibility.

In Table 1 is an overview of all the types

of MIDI-messages, including a list of the most

common.

Normally, commands for light control

belong in the MSC-category among the ‘sys-

tem exclusive messages’. However, if we look

at the list ‘channel voice messages’ to ‘con-

trol change’, then these messages consist of

only 3 bytes: one status byte and 2 data

bytes. Such a control change usually serves

the purpose of altering the parameters of the

sound source, such as, for example, volume,

reverberation, panning, etc.

Most of the possible 128 control changes

(refer to sidebar ‘MIDI-bytes’) are already allo-

cated fixed functions. But, there are also a

few that are free to be used for equipment

The MIDI solution

This idea is not new. Right from the

beginning, with deﬁnition V1.0 from

the MMA (MIDI Manufacturers

Association) were, in the chapter

MSC (MIDI Show Control), defini-

tions for protocols related to the con-

trol of, for example, lights, strobo-

scopes, lasers, film projectors, etc.

These MSC-messages are ‘system-

exclusive’ commands. These com-

mands have a wide range of appli-

cations what immediately means

that they are not easily created or

edited using a regular sequencer.

Besides, an MSC-message for the

control of lights is easily 12 bytes

long. If these MSC-messages are rid-

ing along the same MIDI-interfaces

Table 2. Utilised controllers.

General purpose continuous controller #1

ctrl 16

brightness projector #1

General purpose continuous controller #2

ctrl 17

brightness projector #2

General purpose continuous controller #3

ctrl 18

brightness projector #3

General purpose continuous controller #4

ctrl 19

brightness projector #4

General purpose switch controller #5

ctrl 80

relay projector #1

General purpose switch controller #6

ctrl 81

relay projector #2

General purpose switch controller #7

ctrl 82

relay projector #3

General purpose switch controller #8

ctrl 83

relay projector #4

undeﬁned controller

ctrl 84

extra relay #1

undeﬁned controller

ctrl 85

extra relay #2

undeﬁned controller

ctrl 86

extra relay #3

undeﬁned controller

ctrl 87

extra relay #4

reset all controllers

ctrl 121

all lamps and relays off

‘running status’ is recognised (see text)

3/2001

Elektor Electronics

GENERAL INTEREST

12V

TR1

R33

1N4001

K12

IC2

7 805

K11

C16

C18

100n

C15

IC7

100n

R34

100n

IC7

VAREF

VCC

VPP

AD0

AD1

AD2

AD3

AD4

AD5

AD6

AD7

AD0

AD1

AD2

AD3

AD4

AD5

AD6

AD7

A10

A11

A12

A13

A14

C14

D 1 7

P4.0

P4.1

P4.2

P4.3

P4.4

P4.5

P4.6

P4.7

P0.0

P0.1

P0.2

P0.3

P0.4

P0.5

P0.6

P0.7

2x 9V

1N4001

100mA

1000µ

25V

10µ

16V

4VA5

100n

AD0

AD1

AD2

AD3

AD4

AD5

AD6

AD7

IC15

EPROM

IC6

R26

R12

R10

27256

ALE

P6.0

P6.1

P6.2

P6.3

P6.4

P6.5

P6.6

P6.7

A10

A11

A12

A13

A14

A15

P2.0

P2.1

P2.2

P2.3

P2.4

P2.5

P2.6

P2.7

A10

A11

A12

IC4d

74HC573

IC4c

2n2

CH0

CH1

CH2

CH3

IC16f

IC4

A13

A14

100n

1N4148

R11

270k

C10

A15

IC4 = LM339

C20

P3.0 RxD

80C535

P3.1 TxD

1µ

16V

ZERO CROSS

PSEN

2n2

P3.2 INT0

P3.3 INT1

IC13e

IC16b

SW0

NSW0

P3.4 T0

P3.5 T1

P3.6 WR

P3.7 RD

+VS

PWM0

PWM0E

NSW0E

PWM1E

NSW1E

PWM2E

NSW2E

PWM3E

NSW3E

NSW0

IC4b

R32

IC13b

SW0

SW1

SW2

SW3

SW4

SW5

SW6

SW7

PWM1

IC4a

P5.0

P5.1

P5.2

P5.3

P5.4

P5.5

P5.6

P5.7

SW1

NSW1

2n2

IC11

1N4148

PWM2

D 16

R13

ULN

PWM0

PWM1

PWM2

PWM3

NSW2

IC13c

C11

P1.0

P1.1

P1.2

P1.3

2803

1N4148

PWM3

SW2

NSW2

NSW3

1µ

16V

VEE

CH0

CH1

CH2

CH3

IC13d

P1.4

P1.5

SW3

NSW3

IC3

P1.6

150 Ω

PC900

CLK

C17

C19

IC13a

P1.7

IC16

IC13

SW4

NSW4

100n

RESET

R14

VAGND

100n

R16

VSS

IC13f

8765

1N4148

SW5

NSW5

R15

NSW4

NSW5

+VS

NSW4E

NSW5E

MIDI IN

DIS

33p

C13

33p

IC16e

IC5

R25

220 Ω

JP1

SW6

NSW6

10µ

16V

OUT

K10

555

IC12

THR

RESET

X1 = 12MHz

IC16d

ULN

2803

SW7

NSW7

NSW6

NSW7

NSW6E

NSW7E

C12

IC16a

IC16c

zie tekst

* see text

* siehe Text

* voir texte

IC13, IC16 = 74HC4049

220 Ω

VEE

3n3

MIDI THRU

NSW0E

PWM0E

NSW1E

PWM1E

NSW2E

PWM2E

NSW3E

PWM3E

NSW4E

NSW5E

NSW6E

NSW7E

R19

R20

R21

R23

12V

R37

R36

R35

R38

IC1

IC8

IC9

IC10

RE1

RE2

RE3

RE4

RE5

RE6

RE7

RE8

R28

R27

R29

R30

VDR

MOC3020

R17

R18

R22

R24

000179 - 11

PRJ1

PRJ2

PRJ3

PRJ4

AUX1

AUX2

AUX3

AUX4

Figure 1. Schematic of the MIDI-light-control.

specific functions, for instance. If we select

our light control commands from these avail-

able control changes then, suddenly, every-

thing becomes much simpler. Lights may

now be manipulated in the same way as the

modulation of volume. A nice feature is that

it becomes possible to program the

sequencer to operate a light with the modu-

lation wheel and switch a relay with the sus-

tain pedal. Providing the light mod-

ule with a MIDI-through-connection

means that it can simply be con-

nected in series with the sound mod-

ule using a standard MIDI cable. Of

course, there is the prerequisite that

the sound module does not respond

to the controller commands used by

the light module. These controller

commands have been chosen such

that the risk of interference is virtu-

ally eliminated. The MIDI-light-mod-

ule uses only a couple of controllers

from channel 16 and since MIDI ﬁles

seldom contain these specific con-

trollers there is unlikely to be a prob-

lem. The MIDI-light-controller can

drive 4 projectors and 8 relays when

Elektor Electronics

3/2001

GENERAL INTEREST

face more versatile. Either use the contact to

switch low voltage directly or use an opto-

triac to switch 230 V. This last suggestion can

be implemented by combining an opto-triac

with a power triac and ﬁtting this in an enclo-

sure with built-in plug and socket. This way

everything is safely separated from the 230 V

mains. Never use the relay contacts to switch

230 V directly!

Braun

slide projector

Midi Light

1 = slide transport +

2 = A1

3 = G

4 = slide transport –

000179 - 12a

The hardware

Zeiss Ikon

slide projector

Midi Light

The light module ( Figure 1 ) is built around an

80C535-12 from Infineon (Siemens). It is a

member of the 8051-family with, among other

things, four pulse width modulators built

around timer 2, 7 I/O ports and an 8 channel

A/D-converter. The PWM section performs

the phase control of the mains voltage for the

4 projector lamps.

The PWM outputs each trigger an opto-

triac type MOC3020 (IC1, IC8, IC9 and IC10),

2 = slide transport +

3 = slide transport –

4 = A1

8 = G

000179 - 12b

Figure 2. Connector details of the control terminals of slide projectors from Braun

and Zeiss Ikon.

used with the MIDI-controllers sum-

marised in Table 2 .

the value of the controller. Every

change of state requires an event. A

value of ‘0’ means the contacts are

open, a value of ‘127’ means contacts

closed. This means that the user

deﬁnes the contact closure time.

100 Ω

Possibilities

230V

100n

250V

Control of 4 projectors

The light intensity is controlled by

the value of the controller. Every

change in intensity requires an

event. Value ‘0’ means the light is off

and value ‘127’ means light is on

maximum. The pre-glow is

adjustable and is identical for all four

channels. The lamp characteristics

are linearised.

Driving 4 relays

(Make and break contacts can be

utilised for a variety of purposes)

The relay is controlled in real time by

the value of the controller. Every

state change requires an event.

When the value is ‘0’ the relay is not

energised, when the value is ‘127’

the relay is energised. The DIN con-

nector makes both the make- and

break contact available together

with a 12 V signal via a series resis-

tor. This approach makes the inter-

LOAD

MOC3020

TIC206D

2A T

000179 - 13

Figure 3. Schematic of a circuit to control 230 V

load (max. 2 A).

Control of 4 normally open con-

tacts

(To advance slides, for example)

The relay is controlled in real time by

which in turn ﬁres the power triac internal to

the projector. If a modification to the projec-

tor is necessary, it is limited to the ﬁtting of a

triac. If the projector has a built-in brightness

control it will be sufficient to make the anode-

and gate connections available on the out-

side. A number of common projector connec-

tions are shown in Figure 2 .

To obtain good mains synchronisation of

the pulse width modulators, a zero-crossing-

detector is built around an LM339 quad-com-

parator (IC4) which, every 10 ms, activates

interrupt 0 on pin 32. Careful attention was

paid to the design of this detector to avoid

interference to the light control from the

1350 Hz time code signal that rides on top of

the 50 Hz mains voltage. The AC signal is

tapped from the (highest available) voltage

on the secondary of the mains transformer.

On the outputs of the ﬁrst two comparators,

alternating between them, appears a falling

Running status

MIDI-commands (such as ‘control change’) consist always of a single status byte

followed by one or more data bytes. The status byte deﬁnes the type of com-

mand that is to follow, while the data bytes contain the actual information. In the

case of the control change, for example, the status byte is followed by 2 more

data bytes. The ﬁrst contains the controller number and the second contains the

controller value. When the next MIDI-message is intended for the same MIDI-

channel, it is not necessary to repeat the status byte. This status byte would have

been identical to the previous one. Such successive MIDI-commands of the same

type and for the same channel require only a single status byte, sent at the begin-

ning of the set of messages. A status byte is only transmitted if it differs from the

previous one. This entire mechanism is called ‘running status’. Some older MIDI

equipment is unable to handle the running status. The better sequencers permit

this mode to be switched off.

3/2001

Elektor Electronics

GENERAL INTEREST

000179-1

R30

R29

R27

R28

RE8

RE7

RE6

RE5

IC10

IC9

IC8

IC1

IC12

100mA/T

C20

IC16

IC13

IC11

IC4

R11

C11

C10

R14

IC5

IC3

IC2

D16

D17

K10

Elektor Electronics

3/2001

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: