Midi To Voltage lab

MTV Manual

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Important: The double sided PCB (Printed Circuit Board) has a component side and a soldering side. This is written on the PCB. Be sure to start at the right side.
The layout of the PCB can be downoladed. When you see the pdf file, you will have a good 'chart' of where all the components are placed. It's a good idea to place and solder the components in the right order; start with the resistors and follow the list.

Midi To Voltage lab

Resisitors	[placing the resitors on the printed circuit board]
Capacitors	[placing the capacitors; be aware of the polarity]
Semiconductors	[placing the opamps and da convertors; attention for pin 1!]
Power Supply	[the 7805 generates a steady 5V for the logic]
Misc	[placing the rest of the components]
Jumper Settings	[placing the jumpers]
Circuits	[circuits ofthe mtv-lab explained]
Testing the MTVLab	[test procedure of the new build mtvlab]

Download pdf manual
Download pdf pcb-layout

Component list

Resistors (back to the top)
General: The resistors do NOT have polarity! So, it does not matter how you place a resistor; it works both ways the same. This doesn't count for the array. The array has a common pin; pin 1, indicated with a black dot.

A1 (Array)	10k (see remarks)
P1	10K (see remarks)
R1	33K
R2	220E
R3, R4, R5, R6, R12 t/m R20, R22, R24, R26, R28, R30, R32, R34, R36 t/m R44, R46, R48, R50, R52, R53, R56, R58	10k
R10	470E (Ohm)
< R21, R23, R25, R27, R29 R31, R33, R35, R45, R47, R49, R51, R54 R55, R57, R59	100E (Ohm)

The Resistor array A1 consists of 4 resistors with one common pin; means this array has five pins. Be sure to place it the right way. The pin with the black dot (or stripe) is the pin 1 indication!

P1 is a potentiometer. With this potentiometer the voltage needed for the DA convertor (TLC1452) can be adjusted. It should be adjusted to 2.5V. This can be done when the PCB is finished.

When you are sure all resistors are placed on the right location, solder all the pins and cut them off on the soldering side.

Capacitors (back to the top)
Unlike the resistors, some of the capacitors used on the MTV lab do have polarity! The plus sign is indicated on the Tantalum. In general values less than 1uF (value<<1uF) do not have polarity (this is NOT always true, but in this case it is).

C1, C2	33 pF
C3	3.3 uF (tantalum, polarity!)
C4	10 uF (tantalum, polarity!)
C5	2u2F (tantalum, polarity!)
C6, C7, C8, C9 en C10	<100 nF

Semiconductors (back to the top)

The most vital component on the PCB is the processor, the PIC16F84. It is necessary to place this processor in a socket, which is soldered on the PCB. Do NOT solder the processor itself on the PCB, otherwise it is not possible to re-program the chip. Very important with mounting Integrated Circuits (IC's) on the PCB is to check pin 1 of the chip. On every chip the counting of the pin numbers is anti-clockwise. See figure below:

U0	PIC16F628 (place in Socket!)	Even the socket has got a pin 1 indication. This is to remind you how the processor is placed on the pbc.
U1	LM358 (Opamp)	This opamp creates the reference voltage for the sixteen DA convertors. It can be adjusted with P1
U2	6N138 (Opto Coupler)	The incoming MIDI is connected to the OptoCoupler, so the MIDI signal is electrically devided from the circuit (no problems with connecting a lot of MIDI devices)
U3 t/m U18	LTC1452 (12 bit DA convertor)	Serial input 12-bit DA convertor.
U19 t/m U26	TLC272 (Dual opamp)	These opamps create the 0-10V.
U27	7805 (Voltage regulator)
D1	1N4148 (Diode)
D2,D3	1N4001(4) (Diode)	Diodes D2 and D3 are placed for safety reasons; if the power supply is connected the wrong way, the MTV lab will not blow up.

Misc (back to the top)

X1	10MHZ	The Xtal or Crystal oscillator is placed near the processor and generates a 10MHz clock
J1, J2	4 pins. header
J3 t/m J39 JP1 t/m JP16	2 pins. header
MIDI1	Connection MIDI	Midi in is connected without ground! The ground is only used with Midi out.
MIDI2	Connection MIDI
jumper / Headers: The headers are used for two things: To connect (solder)the wires and to place a jumper. A jumper is just a shortcut between two pins of a header. With the jumpers you can set whether the output is 0-5V or 0-10V.

Powersupply(back to the top)

External adapter, min 12V; max 18V. The component on the picture left is a voltage regulator, 7805. When you apply capacitors (c4 and c5) to avoid oscillation, this device will always generate a clean +5V, also called VCC. The diodes connected to the powersupply input are there for safety reasons.

Jumper Settings: (back to the top)

During start up (power on), the initialisation of the processor takes place. All in- en outputs are defined. It also checks which pins are 'high' (+5V connected to the pin) or 'low' (pin connected to ground). The setting of the jumpers determines the midi channel and midi-controller offset:

Components J1 and J2 consist of 4 pins each. In the table underneath it split up in S4, S3, S2 and S1. Take a look at the photo.

S4	S3	S2	S1	Midi Channel
0	0	0	0	0
0	0	0	1	1
0	0	1	0	2
0	0	1	1	3
0	1	0	0	4
0	1	0	1	5
0	1	1	0	6
0	1	1	1	7
1	0	0	0	8
1	0	0	1	9
1	0	1	0	10
1	0	1	1	11
1	1	0	0	12
1	1	0	1	13
1	1	1	0	14
1	1	1	1	15

The midi controller offset means: the starting midi controller. From that number it will increase +15 (0-15) controllers. Example:
Offset= 32 (J6=0, J5=1, J4=0, J3=0)
The mtv lab will convert incomming controller midi numbers 32-47 into voltage change.

J6	J5	J4	J3	MIDI cntrl number (offset)
0	0	0	0	0
0	0	0	1	8
0	0	1	0	16
0	0	1	1	24
0	1	0	0	32
0	1	0	1	40
0	1	1	0	48
0	1	1	1	56
1	0	0	0	64
1	0	0	1	72
1	0	1	0	80
1	0	1	1	88
1	1	0	0	96
1	1	0	1	104
1	1	1	0	112
1	1	1	1	120

Testing the MTV-lab (back to the top)

Step 1:

First: check the position of all the components placed on the printed ciruit board (pcb). Check all the IC’s (Integrated Circuits). Is pin 1 on the right position? Wait wtih placing the processor untill step 4

Step 2:

Apply a voltage of 12V DC to the plus (+) and minus (-) of the PCB. The right pin of U27 (Voltage regulator 7805) should be +5V now. If this is not het case, shut down the power immediately! Check the wires again. If the power is ok (+5V, or VCC) continue with the test. Always use good wire when connecting the power supply. Make sure that the ground wire is thick enough; low impedant!

Step 3:

Take a voltmeter and connect it to pin 1 (or pin 2) of U1. This is the output of an opamp. This voltage should be adjusted to exact +2.5V. The voltage can be adjusted with potentiometer P1. Look at the figure below. The potentiometer and chip are highlighted.

Step 4:
Place the processor in it’s socket.
Be aware of pin 1. Push the processor in real good;

Step 5:
Connect a midi signal from a computer (or other device) and generate midicontroller number 0, on midi channel 0. Adjust all the jumpers placed at the processor (J3-j6 and S1-S4) to zero. If possible generate a midi signal with slowly changing data, so the voltage change on the output is easy to measure.

On output zero (right upper corner) the voltage should change. The jumper located near the output of the opamp determines whether the output changes from 0-5Volts or 0-10Volts. If the jumper is connected (connection to ground or zero), the output changes between 0-10 Volts. No jumper means 0-5 Volts

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MTV lab circuits (back to the top)

Below in figure 1 the main circuit. All is built up around the PIC16f84 (now a days the pic16F628) and the LTC1452. Midi in (through the 6n138 opto-coulpler) is connected to RB0 of the processor. At startup the processor will check port RA0-RA3 and port RB4-RB7. These jumper (switch) settings determine the midi channel and the controller offset.
The serial DA convertors are connected through RB1-RB3; clocking the data to the right place. Opamp U6 with the potentiometer is there to offer the DA convertors teh right reference value (in this case half the powersupply = 2.5V).
The output of the convertors can be doubled through an opamp (lm358 / tlc272) to create 0-10V output (see figure 2). The pos. power supply of these opamps should be > 10V (on the pcb it is connected to the ext power adapter).

Figure 1:Main circuit MTVlab with PIC16f84 / PIC16f628

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