MIDI Switcher

MIDI SWITCHER is a compact module that functions as a MIDI triggered, 8 port power switch. It comes fully assembled and tested and is a replacement for my previous MIDI Switcher DIY Kit, with improved features and functionality

MIDI SWITCHER allows you to use your MIDI keyboard, sequencer or DAW to control low voltage DC loads such as:

• Solenoids/actuators (think robotic percussion!)
• DC Motors
• Relays
• High power LEDs (with appropriate voltage and heat sinking)
• Filament bulbs

It is perfect for making electro-mechanical musical instruments, controlling light shows from your DAW, making crazy robotic sound art installations or just about anything else you can think of!

MIDI SWITCHER is a “low side” power switch, which means that it switches between the (-) terminal of the connected device and power supply (-) terminal. It can switch DC currents that are referenced to ground, but not AC currents, signals or DC currents that are not referenced to ground (these limitations can be bypassed with an additional relay, with the MIDI SWITCHER driving the relay coil)

THIS DEVICE IS NOT SUITABLE FOR DIRECTLY SWITCHING MAINS ELECTRICITY Mains can be switched via an additional relay but I do not advise this unless you are qualified and experienced with working with main power!

Each of the eight outputs can be triggered by

• MIDI notes (with optional velocity range filter),
• MIDI continuous controller messages (with configurable value range filter)
• MIDI Program Change messages.

The switching pulse can then be “shaped” as follows

• Switching lasts for specified “hold” duration and/or length of the trigger condition. The hold time can be modulated by note velocity or by a separate MIDI CC with settings from 10 milliseconds to 16 seconds.
• Switching power can be controlled using pulse width modulation (PWM). The PWM duty can be modulated can be modulated by note velocity or by a separate MIDI CC. Four of the outputs use hardware PWM to achieve highly stable control at ~1kHz carrier (the other four outputs use software PWM at around 150Hz)
• Gamma correction and “release” envelope for PWM duty are ideal for controlling LED strobe effects.

MIDI SWITCHER is configured by MIDI System Exclusive (Sysex) files and a web form is used to configure it. Submitting new settings immediately downloads a Sysex file to be sent to your switcher. Try the web form at http://www.six4pix.uk/switcher/patch.asp

MIDI SWITCHER has flexible power options including a 2.1mm socket for low power applications and screw terminals for higher power. A power link jumper enables the microprocessor power circuit to be disconnected from the loads, allowing them to run at up to 100V DC and 8A per output. I recommend that the total continuous current through the board be limited to 8A, but higher currents can be supported in pulsed applications (such as solenoids). The main thing is to ensure the supply is adequate for the loads and nothing on the board is overheating during use.

Two MIDI SWITCHERs can be connected with a single additional wire to allow them to share a single MIDI input and power supply. More switchers can be used in an application if an external MIDI splitter is used. The hardware features

• Optically isolated, 5-pin DIN MIDI input and “shared MIDI bus” connector for pairing switchers.
• 2.1mm centre positive barrel socket which can take from 7V up to 30V at 2A and be used as the sole supply input in low power applications
• Screw terminals which can take 100V and 8A (recommended max continuous) to separately supply high power load (When isolated via power select jumper)
• A pair of screw terminals for each of the 8 outputs. High side is permanently connected to the supply, low side is switched via transistor
• An indicator LED for each output which shows when the output is switched and the PWM duty (via dimming)
• MIDI activity and power LEDs
• Reset button sets all outputs back to power on state. Long press sets switcher to MIDI ignore mode – this help configure multiple switchers one at a time when on a common MIDI input
• PCB traces are 2 oz copper for improved current capacity and heat dissipation.
• Transistors (MJD-122) feature built in flyback diode for inductive loads
• Bootloader allows future firmware updates via MIDI
• Open source hardware and firmware
• Dimensions 104 x 41 x 23mm, weight 46g (without legs attached)

MIDI SWITCHER CANNOT BE USED DIRECTLY TO SWITCH MAINS ELECTRICITY. NEVER CONNECT THIS DEVICE DIRECTLY TO THE MAINS

Here is a demo video, courtesy of MIDI-Error!