Fullscreen HTML5Med Res (??MB)HTML4

An up-to-date MIDI interface for PCs USB MIDI-Mate Use your PC to link up MIDI synthesisers, keyboards and various instruments. Most modern PCs make good sequencers for electronic music making, with readily available software and the drivers built into the latest versions of Windows. This USB-MIDI interface provides all the hardware you’ll need. By JIM ROWE T EN YEARS AGO, in the February 2001 issue of SILICON CHIP, we described a project called the MIDI-Mate – an easy-to-build MIDI interface to go with the PCs that were then available. At that stage, most PCs had either no built-in MIDI port at all or just a rudimentary MIDI port tucked away inside their sound card and available only via a couple of pins on the sound card’s game port. The original MIDI-Mate was designed to expand those crude MIDI “core ports” into a full MIDI port which could be hooked up to any standard MIDI synthesiser, instrument or keyboard using standard MIDI cables. The unit was pretty popular and 72  Silicon Chip we think this updated USB version will be too. Now it’s true that basic USB-MIDI adaptor cables are already available at fairly low cost, offering a MIDI IN and MIDI OUT port at the end of a cable which plugs into a PC’s USB port. But these devices only offer the bare minimum of MIDI interfacing facilities. There’s no MIDI THRU output linked to the MIDI IN jack and only a single MIDI OUT jack, which restricts you to a very simple set-up. Our aim in developing our new USB MIDI-Mate has been to come up with an up-to-date interface offering the same expanded MIDI ports as our original unit. At the same time, the cost should be only slightly higher than a USB adaptor cable. As with the original MIDI-Mate, it’s powered directly from the PC so no separate power supply is needed. What it does This unit provides a 2-way serial communications “bridge” between one of the USB ports on a PC and external MIDI devices. This enables the PC to send a MIDI music file out to a synthesiser and/or other electronic musical instruments via the interface’s MIDI OUT jacks. In addition, the PC can receive MIDI messages from a keyboard or other MIDI controller, via the interface’s MIDI IN jack. siliconchip.com.au The rear panel provides access to the Type-B USB socket and a reset switch. The two LEDs show the USB status and blink alternately when the device is plugged into a computer and working correctly. Both the MIDI IN and MIDI OUT messages are relayed to and from the PC (and the software running on it) via a single USB cable. Considering that USB is a serial bus and MIDI is also serial data communication, you’d perhaps expect that an interface bridging between the two would be quite straightforward – a bit like a couple of UARTs (Universal Asynchronous Receiver Transmitters) connected back-to-back. It’s not quite that easy though, largely because of the protocols that must be used when any kind of data is sent over the USB. That’s because all USB communication is controlled by the host (ie, the PC) and the device at the other end of a USB cable is not free to upload any data it likes, whenever it likes. In addition, each MIDI message sent over the USB needs to be “packetised” (packaged into a standard USB data packet) with an identifying header byte attached to the start of the packet – a bit like an address label. This is to ensure that each packet reaches the correct destination at the receiving end. Quite apart from these complications, any USB device also has to provide answers to a standard set of questions from the host PC as soon as it’s plugged into a USB port. This rigmarole is known as the “enumeration sequence”, because the host needs to know quite a lot about the device before it can give it a USB address and install the appropriate drivers so its software can communicate with the device correctly. siliconchip.com.au Parts List: USB MIDI-Mate 1 PCB, code 23110111, 117 x 102mm 1 low-profile instrument case, 141 x 110 x 35mm 4 5-pin DIN sockets, 90° PCBmount 1 SPST momentary tactile push­ button switch, 90° PCB-mount (S1) (Jaycar SP-0607) 1 12MHz quartz crystal (X1) 1 Type B USB socket, PCB-mount (CON1) 4 5-pin DIN sockets, 90° PCBmount (CON2-CON5) 1 6-way section of SIL pin strip 1 20-pin DIL IC socket 1 14-pin DIL IC socket 1 8-pin DIL IC socket 4 small self-tapping screws, 6mm long 1 M3 x 6mm machine screw with M3 nut & washer 100mm tinned copper wire for links In short, even though our little USBMIDI interface is just acting as a 2-way communications bridge, it needs to be based around a microcontroller to handle the USB enumeration and communications protocols. In this case, we’re using a PIC18F14K50 microcontroller, which is about the smallest and lowest-cost device available with an in-built USB module, as well as a USART module capable of working at the MIDI data rate of 31.250kHz. Semiconductors 1 PIC18F14K50 microcontroller programmed with 2311011A.hex (IC1) 1 74HC04 hex inverter (IC2) 1 6N138 optocoupler (OPTO1) 1 IRF9540 P-channel MOSFET (Q1) 3 3mm red LEDs (LED1, LED3, LED4) 1 3mm green LED (LED2) 1 1N4148 diode (D1) Capacitors 1 10µF 16V RB electrolytic 1 470nF MKT metallised polyester 2 100nF MKT metallised polyester 2 22pF NP0 ceramic Resistors (0.25W 1%) 1 33kΩ 9 220Ω 1 10kΩ 1 47Ω 2 470Ω 1 2.2Ω 2 330Ω The USB module inside the PIC18F­ 14K50 is actually pretty impressive. It includes a full-speed and low-speed compatible USB serial interface engine (SIE) plus a USB transceiver so that it can connect directly to a USB cable. It takes its clock signals from the PIC’s main clock circuitry, which in this case also includes a frequency-multiplying phase-locked loop (PLL) to provide a 48MHz clock derived from the external 12MHz crystal. October 2011  73 74  Silicon Chip siliconchip.com.au 4 1 22pF GND 3 2 22pF X1 12MHz D+ D– 18 D–/RA1 3 2 19 OSC2/RA4 OSC1/RA5 D+/RA0 20 Vss RB4/SDA RB5/RX RB6/SCK RB7/TX RC0 RC1 RC2 RC3 RC4 RC5 RC6 VUSB RC7 IC1 PIC18F14K50 RA3/MCLR S1 USB MIDIMATE SHLD CON1 TYPE B 4 Vdd 1 RESET 10k 100nF Vbus (+5V) 13 12 11 10 16 15 14 7 6 5 8 9 17 G 33k 470 K D 220 220  LED1 A 47 470nF S Q1 IRF9540 470 K  LED2 A +5V = SUSPEND 0V = ACTIVE 10 F 16V 2.2 A K K A 330 LED3 MIDI IN/THRU 330 D1: 1N4148 K LED4  MIDI OUT A  13 11 4 IC2f IC2e IC2b 14 5 6 8 12  IC2c 3 2 IC2a 7 IC2d +5V 1 9 5 OPTO1 6N138 IC2 74HC04 10 3 +5V (WHEN ACTIVE) K A 2 8 6 LEDS A K D1 1N4148 220 220 220 220 220 220 220 100nF G D 5 4 5 5 CON2 CON3 CON4 CON5 S IRF9540 4 2 4 2 4 2 5 D MIDI IN MIDI THRU MIDI OUT 1 MIDI OUT 2 Fig.1: the circuit is based on a PIC18F14K50 microcontroller (IC1) which handles USB enumeration and exchanges MIDI data packets with the PC via USB connector CON1. The 6N138 optoisolator (OPTO1) provides the necessary isolation for the MIDI IN socket, while inverters IC2a & IC2c-IC2f buffer the signals to the MIDI OUT & MIDI THRU sockets. IC2b drives LED4 which blinks when there is activity on the output sockets, while Mosfet Q4 switches off the power to IC2 and OPTO1 when the PC (via IC1) instructs the device to enter “suspended” mode. 2011 SC  USB 6 5 4 3 2 1 CON6 T1G ICSPCLK ICSPDAT GND Vdd Vpp ICSP CONNECTOR Vbus The MIDI Standard: What It Is & How It Works MIDI is an acronym standing for Musical Instrument Digital Interface. It’s a standardised system for communicating between electronic musical instruments, keyboards, controllers and sequencers (including PCbased sequencers). The MIDI standard was agreed on by a group of musical instrument makers in 1983 and has been used and extended since then. MIDI relies on serial data communication at 31.25kb/s using asynchronous 5mA current loop signalling, with the current provided by the “transmitting” end. This means that each byte of a MIDI message takes only 320μs to be transmitted (counting start and stop bits). Since MIDI messages are either one, two or three bytes in length, this means that over 1000 such messages can be sent each second via a single MIDI cable. Each MIDI cable carries only one signal, so for bi-directional communication, two cables must be used. The cables themselves use shielded 2-conductor wire. All MIDI cables are fitted with standard 180 ° 5-pin DIN plugs at both ends. However, only pins 4 & 5 are used for the actual current loop signalling (wired 4-4 and 5-5). Pins 1 & 3 are left unconnected, while the shield braid is connected to pin 2 at each plug. Inside MIDI equipment, pin 2 is connected to earth only on MIDI OUT sockets. This allows correct earthing of the cable shield braids, without creating earth loop problems. Unlike most other current-loop signalling, Data can be exchanged very efficiently between the PIC’s CPU and the USB module’s SIE. That’s because they share a 256-byte dual-port static data RAM (SRAM), with each side controlling one of the ports. Circuit description Now refer to the full circuit shown in Fig.1. The heart of the circuit is IC1, the PIC18F14K50. This does all the real work of the interface, exchanging data packets with the PC via USB connector CON1 which connects directly to pins 18 & 19, the transceiver pins of the PIC’s USB module. On the MIDI side, the outgoing MIDI messages from the PC emerge from pin 10, which is the serial data output of the PIC’s USART module. Incoming MIDI messages enter the PIC via pin 12 – the USART module’s serial data input. siliconchip.com.au current only flows in a MIDI link when data is actually being transmitted. This allows MIDI cables to be plugged and unplugged without any problems, as long as data is not actually being transmitted at the time. To prevent equipment damage due to wiring errors or component faults, all MIDI inputs are provided with 3kV of galvanic and electrostatic isolation via an optocoupler. For correct MIDI communication between equipment, a MIDI OUT or MIDI THRU socket at one end must be connected to a MIDI IN socket at the other. In most MIDI systems, there is a single main controller or sequencer (often the computer), from which most of the MIDI messages originate. When these messages must be sent to more than one instrument, they can be distributed in either “star” or “daisy-chain” manner as desired. There’s no need to worry much about the actual code messages sent over the MIDI links, because nowadays this is all handled by sequencer or other software running in the PC and by firmware running in the other instruments and keyboards. It’s probably enough to know that most MIDI messages are short commands to allocate a particular instrument to a particular channel, to tell it to start or stop playing a particular note, to change the instrument’s attack/decay or other performance parameters, and so on. As mentioned earlier, these commands are generally in the form of three-byte messages, although some configuration and/or The rest of the circuitry outside IC1 is mainly used to condition the incoming and outgoing MIDI messages. This is necessary because the MIDI system uses current-loop transmission and requires all inputs to be provided with high-voltage isolation using an optocoupler. OPTO1, a 6N138 highspeed device, provides the necessary isolation for the MIDI input jack CON2. It also acts as a current-to-voltage converter so that incoming MIDI messages are converted into voltage levels to feed pin 12 of IC1. By the way, don’t be tempted to try substituting another optocoupler for OPTO1. Most other optocouplers don’t have the switching speed of the 6N138 and won’t give reliable transfer of MIDI signals. Two of the inverters inside IC2 (a 74HC04 hex inverter) are used to take the incoming MIDI messages from pin system management messages are only one or two bytes long. Using a PC-based music editing and sequencer program, and perhaps with a MIDI music keyboard to feed in the actual notes, you can assemble a complete sequence of MIDI commands to play a piece of music – eg, on the “instruments” in a synthesiser. The synthesiser can then be made to “perform” that piece of music simply by sending the sequence to it, via the MIDI link. When you’re happy with the result, you can save the sequence on disk as a MIDI music file. These have a standardised format and are identified with a “.MID” extension. Discs with collections of pre-composed MIDI music files are also available and you can download them from the internet as well. It’s important to realise that although a MIDI music file may look superficially similar to a .WAV file of a digital sound recording, it’s really quite different. It’s more like an electronic equivalent of sheet music – simply a sequence of detailed instructions describing how to play the music. In this case, it’s instructions for electronic instruments rather than for human players. Finally, if you do want to delve more into the technicalities of MIDI, you’ll find quite a bit of useful reference information on the MIDI Manufacturers Association website at www.midi.org/techspecs There are also some very helpful detailed explanations at home.roadrunner. com/~jgglatt/tech/midispec 6 of OPTO1 and convert them back into current-loop form to drive the MIDI THRU output jack (CON3). Three of the remaining inverters are then used to convert the outgoing MIDI voltagelevel signals from pin 10 of IC1 into current-loop form to drive the two MIDI OUT jacks CON4 and CON5. The remaining inverter is used to drive LED4, which blinks to indicate activity on the MIDI output jacks. LED3, which is connected in series with the output load of OPTO1, provides the same kind of activity indicator for the MIDI IN and MIDI THRU jacks. The two remaining LEDs in the circuit, LEDs1 & 2, are driven directly from pins 15 & 16 of IC1. These are used to indicate the USB status of IC1 and hence the status of the interface as a whole. When the interface is correctly enumerated and configured for October 2011  75 3 1 2 LED1 IC1 PIC18F14K50 X1 CON3 5 4 4 2 LED3 MIDI IN/THRU K A MIDI THRU MIDI IN K 5 220 220 220 220 CON4 LED4 MIDI OUT CON5 4 5 4 2 2 MIDI OUT1 MIDI OUT2 A Fig.2: here’s how to install the parts on the PCB. Make sure that IC1, IC2 and OPTO1 are correctly orientated and check that all sockets are flush against the board before soldering their leads. use, these LEDs blink alternately at about 1Hz. Power supply As mentioned earlier, the interface circuit receives its power from the host PC via the USB cable, so it’s a “bus powered” device. IC1 is powered directly from the Vbus line (pin 1 of CON1), while IC2 and OPTO1 receive their power via Q1, an IRF9540 Pchannel Mosfet used here as a switch under the control of IC1 via pin 14 (RC2). The idea behind this is that all buspowered USB devices must reduce their total current drain to a very low level when the host PC sends them to allow manual resetting of the PIC, if this should ever be needed. The only other item that we haven’t as yet mentioned is CON6, a 6-pin SIL pin strip which provides an ICSP (In Circuit Serial Programming) interface. This allows the PIC to be programmed in-circuit using a programmer like Microchip’s PICKit3. Construction 22pF 330 330 220 220 D1 4148 11101132 1102 © IC2 74HC04 CON2 5 ETA MIDI M BSU 10 F 220 OPTO1 6N138 12MHz K A 100nF 2.2 22pF LED2 K A 470 470 4 1 100nF 10k CON6 ICSP 47 33k CON1 USB IN 220 220 Q1 IRF9540 S1 470nF RESET into suspended mode. It does this by simply not sending them any “stay awake” token packets for a period of 3ms or more. In this circuit, as soon as IC1’s USB module senses that it should enter suspended mode, it turns Q1 off and thereby switches off the power to IC2 and OPTO1. When the PC directs IC1 to “wake up”, it switches Q1 back on again and restores power to IC2 and OPTO1. The average current drawn by the interface circuit from the host PC via the USB cable when it’s not suspended and operating is around 22mA. Crystal X1 on pins 2 & 3 of IC1 is the resonator for the PIC’s main clock oscillator, while switch S1 is provided All the components used in the USB MIDI-Mate are mounted on a single PCB coded 23110111 and measuring 117 x 102mm. This mounts inside a standard low-profile plastic instrument case measuring 141 x 111 x 35mm. The Type-B USB connector CON1 used to connect the interface to the host PC is mounted in the centre along the rear edge of the board, with LEDs1 and LED2 on one side and S1 on the other. The four 5-pin DIN sockets used for the MIDI jacks (CON2-CON5) are spaced along the front edge of the board, with LED3 and LED4 in the centre. All connectors and LEDs (together with S1) are accessed via matching holes in the rear and front panels. Fig.2 shows the parts layout on the board. Fit the wire links, resistors and capacitors first, then fit Mosfet Q1. The latter comes in a TO-220 package and mounts flat on the top of the board at upper left, with all three leads bent downwards by 90° about 6mm from its body. Its tab is then fastened to the board using an M3 x 6mm machine screw, washer and nut, after which the leads are soldered to their PCB pads. Capacitor Codes Value 470nF 100nF 22pF µF Value IEC Code EIA Code 0.47µF 470n 474 0.1µF 100n 104    NA   22p   22 Resistor Colour Codes o o o o o o o o No.   1   1   2   2   9   1   1 76  Silicon Chip Value 33kΩ 10kΩ 470Ω 330Ω 220Ω 47Ω 2.2Ω 4-Band Code (1%) orange orange orange brown brown black orange brown yellow violet brown brown orange orange brown brown red red brown brown yellow violet black brown red red gold brown 5-Band Code (1%) orange orange black red brown brown black black red brown yellow violet black black brown orange orange black black brown red red black black brown yellow violet black gold brown red red black silver brown siliconchip.com.au OPTO1 into their respective sockets. All three are orientated with their notched ends to the left. Installing the board into the recommended case is straightforward. Fig.3 shows the drilling templates for the front and rear panels. Once the holes have been drilled, reamed and filed to shape, download the two panel artworks (in PDF format) from the SILICON CHIP website and print them out. The labels can then be laminated and attached using doubled-sided adhesive tape. Cut out the holes in the labels using a sharp hobby knife. That done, the PCB assembly can be lowered into the bottom half of the case along with the front and rear panels. It’s secured using four 6mm-long self-tapping screws, which mate with four of the moulded mounting pillars. Your USB MIDI-Mate is now complete and ready for use. There are no adjustments or setting up needed; if you have assembled it correctly, it should be ready for use immediately. This view shows the assembled PCB, ready for installation in the case. Note how the four LEDs are mounted (see text). The USB connector (CON1) and the four DIN sockets (CON2-CON5) can now go in. Make sure they all sit flush against the PCB before soldering their pins. You can then fit the three sockets for IC1, IC2 and OPTO1, followed by pushbutton switch S1 and the 6-pin SIL strip (CON6). The four LEDs are next on the list. The two red LEDs between the MIDI sockets should first have their leads bent down through 90° some 5mm from their bodies. These LEDs are then installed so that the horizontal sections of their leads are 11mm proud of the board (use an 11mm-wide cardboard spacer to set this). Similarly, the red and green LEDs adjacent to the USB connector (CON1) Fig.3: this drilling template for the front and rear panels can be downloaded (in PDF format) from the SILICON CHIP website. Use a small pilot drill to start the holes before enlarging them to the correct sizes (see text). have their leads bent down through 90° about 3mm from their bodies. These LEDs are then installed 7mm proud of the board. If you are building the USB MIDIMate from a kit, the PIC18F14K50 microcontroller will have been preprogrammed with the correct firmware. However, if you’re building the project from scratch, you’ll either have to purchase a programmed PIC­ 18F14K50 from SILICON CHIP Publications or program it yourself. If you do elect to program it yourself, the firmware (2311011A.hex) can be downloaded from the SILICON CHIP website. The PCB assembly can now be completed by plugging the two ICs and 25 20.5 A 16 Plug and play As soon as you connect the USB MIDI-Mate to a PC running Windows XP (SP3), Vista or Windows 7, Windows should detect it and go through the USB enumeration process before finally indicating that the device is ready to use. If you then glance at the rear of the interface, you should see that LED1 and LED2 are blinking on and off alternately. This indicates that the USB MIDI-Mate is enumerated, “awake” and ready for business. You can also confirm that everything 16 12 A B B 20.5 A A 30.5 15.5 FRONT PANEL 134.5 8 9 44 B 12.5 11.5 B 11.5 REAR PANEL 11.5 49.5 30.5 C 6.5 HOLES A: 16.0mm DIAMETER; HOLES B: 3.0mm DIAMETER; HOLE C: 4.0mm DIAMETER siliconchip.com.au 24.5 10 ALL DIMENSIONS IN MILLIMETRES October 2011  77 MIDI THRU MIDI OUT MIDI OUT USB IN/OUT USB STATUS LED2 RESET LED1 USB MIDI MATE MIDI OUT USB MIDI MATE MIDI IN SILICON CHIP SILICON CHIP MIDI IN/THRU Fig.4: these front and rear panel labels can be down­loaded in PDF format from the SILICON CHIP website. They should be laminated and attached to the panels using doublesided adhesive tape. Fig.5: when connected to a PC, the unit should appear in Device Manager as a “USB MIDI Interface”. Fig.6: in Windows XP, “USB Audio Device” should be listed here as one of the MIDI Music Playback devices. Fig.7: “USB Audio Device” should also appear in this list when the Hardware tab is clicked (XP). is correct by checking the Device Manager settings. For both XP and Windows 7, launch Device Manager (via the Control Panel) and expand the “Sound, video and game controllers” listing. You should see “USB MIDI Interface” listed – see Fig.5. If you then right-click this entry and click Properties, you should see a dialog telling you that “This device is working properly”. Note that if you are using Windows XP, it may be necessary to allow the operating system to search the Internet for a suitable driver to install when the interface is initially connected. Once it’s installed, it should show up in Device Manager. In addition, if you open Control Panel, double-click “Sounds and Audio Devices” and then click on the Audio tab, you should see “USB Audio Device” listed as one of the MIDI Music Playback devices (see Fig.6). If you now click on the Hardware tab, you should find the “USB Audio Device” listed there as well. If you select this and click on the Properties button, its Location should be shown as “Location 0 (USB MIDI Interface)”. And in the Device Status box, you should again see the message “This device is working properly”. loaded for free – “Notation Player” and “Anvil Studio 2011”. Notation Player is a MIDI music player application that can be downloaded at no cost from www.notation. com It not only lets you play virtually any MIDI music file but also shows the file’s musical notation on the screen while it’s playing. Anvil Studio 2011 is a bit more elaborate. It’s not only a MIDI music player but a recorder and sequencer as well. Written by Willow Software, it can be downloaded free from www. AnvilStudio.com As well as displaying a MIDI music file’s notation on the screen, Anvil Studio 2011 will also let you check your MIDI OUT and MIDI IN connections via the USB MIDI-Mate, show- 78  Silicon Chip The software to use Since the USB MIDI-Mate is compliant with the USB and MIDI specifications, it works fine with any of the common MIDI music player and sequencer applications. While developing and testing the project, we used two applications that can be down- siliconchip.com.au Helping to put you in Control Control Equipment 4-20mA Current Source provides a cheap 2 wire 420mA signal to test PLCs, indicators or other controllers. Can also be used with a potentiometer to provide a remote setpoint. KTC-266 $79.00+GST The PCB assembly is secured inside the case using four self-tapping screws which go into integral pillars. ing you the MIDI messages on-screen at the same time. This is very handy for troubleshooting MIDI cables and instruments, etc. Assuming that you have a synthesiser or other MIDI instrument connected to the USB MIDI-Mate, getting it to “play” should now simply be a matter of starting up your player or sequencer application, loading a MIDI file and then clicking on the “Play” button. While the file is playing, LED4 on the front panel should blink as the MIDI messages stream out to the synthesiser. Similarly, if you have a MIDI music keyboard or other controller, you’ll now be able to hook its MIDI OUT to the MIDI IN jack on the USB MIDIMate and record your own music to the computer’s hard disk – after clicking on the sequencer program’s “Record” button, of course. And that’s really all there is to it. With the USB MIDI-Mate and a suitable application like Notation Player or Anvil Studio 2011, your computer will have everything it needs to become a powerful MIDI music player and/or sequencer. The rest is up to you and your musiSC cal creativity. Industrial Pushbutton Indicators 22mm dia. Fitted with interchangeable contact block and 24V or 240VAC LED bulbs. Red, green, white and yellow available. HER-221 $11.95+GST Temperature Humidity Transmitter 420mA or 0-10V outputs. Fitted with remote sensors on 1.5m cable RHT-040 $279.00+GST 24V Surge Suppression Terminals Protect your 4-20mA signals with these DIN rail terminal fitted with a 1KA/2KA MOV. TRM-160 $3.00+GST Bidirectional Brushed Motor Speed Controller Supports USB, serial, analog input and RC interface. Suitable for 12/24VDC motors up to 12A. POL-1379 $49.95+GST Load Cell Amplifiers Compact and easy to use these are available for load cells with 1,2 or 3 mV/V output. Select 0-10V or 4-20mA outputs. AXS-501 $99.00+GST 30A Relays fitted with 2 DPDT contacts. Available with 12VDC, 24VDC, 24VAC and 240VAC coils HER-030 $7.95+GST The two USB Status LEDs, the USB socket and the Reset switch are accessed via the rear panel. siliconchip.com.au Contact Ocean Controls Ph: 03 9782 5882 www.oceancontrols.com.au October 2011  79