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MIDI 16-Way Drum Pad Triggers to control LEDs via Relays


16-Way  DRUM Triggers to LEDS 


This design is a 16-way drum pad trigger system with the velocity switching relays to control 16 groups of Green, Blue and Red Light Emitting Diodes (LEDs).


Each of the 16 drumpad/piezo triggers is fed to a Sample and Hold circuit via a 6.35mm  Mono Jack Socket. It is then fed to an Analog input on the ATmega Mega microcontroller board where the velocity of the drum 'hit' is measured.


If no drums are hit then the Green LEDs are On, the Blue LEDs are Off, and the Red LEDs are Off.
For a Low or Medium Hit the Green LEDs are Off, the Blue LEDs are On, and the Red LEDs are Off.
For a greater than medium hit the Green LEDs are Off, the Blue LEDs are On, and the Red LEDs are On. 


Also the 16 drumpad/piezo triggers produce a velocity sensitive MIDI Out signal, providing a full (0-127) velocity range, which can be adjusted using the 1m ohm pre-set resistor in the Sample and Hold circuit. The drums are pre-selected to the MIDI outputs 35-50 for the piezo drumpads.  The unit uses MIDI Channel 10, the standard drum channel. The 16 drums are drum selections 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 and 50. The MIDI drum selections for General MIDI drums.


The unit also has 6 Jack Sockets for 6 footswitch pedal inputs, to send MIDI Note ON/Off, the notes are 60, 62, 64, 65, 67 and 69 which are the C, D, E, F, G and A above middle c=60. These notes are transmitted on MIDI Channel 1.




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PRICE:  €250.00




The 16-Way drum inputs to LEDs via Relays unit utilizes:

  • An Arduino Mega board including a suitable pre-programmed Atmega microcontroller,
  • A 2.1mm power socket, and associated LED, 
  • 16 Jack Socket Inputs,
  • 16 sets of Rectifier and sample and hold circuits,
  • 16 pre-set resistors on inputs to adjust for drum trigger sensitivity,
  • 16 inputs are velocity sensitive, providing a full (0-127) velocity range,
  • 6 Jack Sockets for 6 footswitch pedal inputs,to send MIDI Note ON/Off commands,
  • 16 Buffer 5 Volt Relays for 12 V Green/Blue LED strip,
  • 16 Buffer 5 Volt Relays for 12 V Red LED strip,
  • A MIDI 5-pin DIN output socket,


The 16-Way drum inputs to LEDs via Relays unit requires:

  • A suitable 12 Volt DC power supply,
  • 16 off piezo drumpad triggers,
  • 6 off foot-pedals ( if required),
  • External Green, Blue and Red 12 Volt LED strips.



The 16-Way drum inputs to LEDs via Relays unit circuits:


Sample and Hold Board:

The Sample and Hold (S/H) board consists of 16 S/H units each consisting of an adjustable 1m ohm pre-set potentiometer resistor, which adjusts the sensitivity for the drumpad hit. Adjusting the potentiometer in a Clockwise manner increases the sensitivity and adjusting the potentiometer in an Anti-clockwise manner decreases the sensitivity. These potentiometers can then decide what represents a medium or hard drum 'hit'. After the potentiometer the signal is fed to a BAT85 Schottky diode, where it is rectified, and then fed to the charge storage capacitor of 100 nF and parallel resistor of 1m ohm. This RC time constant is about: 

RC = 1x 10^6  x 100 x10^-9  = 100 milliseconds. 


After any input 'hit' is detected the software shorts out this charge storage capacitor to prevent multiple triggers and to allow detection of fast drumming.


Jack Socket Foot-Pedal Wiring:

The 6 input foot-pedals use MONO jack sockets, using standard 6.3mm (¼in) style switched 2-pole MONO jack socket with 2-poles switched upon insertion of the jack plug. This design uses a switched Ground (GND,  0 Volt) connection.


Microcontroller Board:

The ATmega Mega microcontroller board scans the 16 Analog inputs and when a drum 'hit' is detected the velocity is measured and the corresponding Relays are switched ON which then switch On the appropriate colour LEDs, and a MIDI Note On is sent on MIDI Channel 10, the standard drum channel.


Also the 6 foot-pedals are monitored and if one or more of them is operated then a MIDI Note On is sent on MIDI Channel 1.


Relay Boards:

The Relay Board are 'Active Low', this means when a low voltage (0 Volt, GND) is applied to the input pin the relay is switched On. 
This system uses four 5V 8-Channel Relay interface boards. Two of the boards are used to produce 16 outputs for the Green/Blue Leds and two of the boards are used to produce 16 outputs for the RED LEDs.


Each input of the relay boards uses an opto-isolater and needs needs 15-20mA driver current. The high-current relay outputs can switch up to: AC250V 10A  and up to DC30V 10A. There is also an indication LED for the output status of each of the Relays. 



The MIDI OUT connection uses 5-Pin 180 degree DIN sockets. Note that the MIDI Out socket is polarised and the correct pins should be used.  The MIDI Out Socket is connected via two series 220 ohm resistors. This unit works in standard MIDI mode, at a MIDI Baud rate of 31250. 


Power Supply:

External power can come either from an AC-to-DC adapter or battery. The adapter can be connected by plugging a 2.1mm center-positive plug into the board's power jack. Leads from a battery can be inserted in the Gnd and Vin pin headers of the POWER connector. A low dropout regulator provides improved energy efficiency.


The board can operate on an external supply of 7 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable. If using more than 12V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 volts.


Note that with the Arduino Mega the power input selection (USB/EXT.) is automatically selected.