8-Way MIDI DRUM PADS

Have you got rhythm? Do you want to transfer that  rhythm to your computer or hardware sequencer?  Probably the easiest way of achieving this is to  use MIDI drum pads that can be hit with  drumsticks, and the data can be stored in real time with any errors corrected afterwards. 

I previously designed a MIDI drum pad system with the velocity byte fixed at maximum. Now I have designed an 8-way velocity sensitive circuit and built this unit based around the PIC 16F877 microcontroller.  

It provides MIDI data which has to be sent to a drum/synthesiser or sound module. The velocity byte is dependent on how hard the piezo transducer is hit.  The drum selection is completely programmable, and the MIDI transmit channel is programmable. However, normally the drum sounds are assigned to MIDI channel 10.

The 8-Way drum inputs to MIDI Output unit utilizes:

• A Printed Circuit Board (PCB), 
• a pre-programmed 16F877 PIC,
• The drum selection is completely programmable from 0-127,
• They circuit is velocity sensitive,
• The MIDI transmit channel is  programmable (1-16),
• A PCB screw terminal power socket and 9v battery connector,
• PCB screw terminals for 8 drum-pad inputs,
• A 16 x 2 Liquid Crystal Display (LCD), 
• 3 control switches to  select the menus, increment and decrement the drum and MIDI channel values,
• A MIDI 5-pin DIN output socket,
• Each input (1-8) is selectable to a particular MIDI drum selection ,
• The circuit schematic is available in GIF format,
• The circuit consists of the  drum microcontroller layout and the 8-way pre-amplifier layout, (if required).

The 8-Way drum inputs to MIDI Output unit requires:

• A 9v battery or equivalent DC power source,
• Suitable external  piezo-electric transducers,
• Sensitivity can be increased with the 8-way pre-amplifier.

There are two modes of operation:

1. Programme Mode
2. Normal Mode

Programme Mode:

Programme Mode is entered by pressing the Menu switch ON. Normal Mode is entered by having the Menu switch OFF at power-on. Each time the menu switch is pressed the next menu is selected from 1 to 14.

The value for each selected menu item can be increased or decreased using the increment and decrement switches, respectively. The available menus are shown on the LCD displays.

The MIDI Channel is normally set to channel 10 for drums, but it can be set to any midi channel (1-16).

Programming the Drum to MIDI Unit only has to be done once and the drum values are stored internally in the EEPROM and the unit will continue to operate in this mode, even when power is removed, until reprogrammed. 

The adjustable Threshold value (0-127) is used to prevent false triggering from adjacent drum triggers or external noise. It is initially pre-set to a value of 11.

The adjustable Sensitivity value (0-127) is used to increase the value detected from the piezo transducer if low sensitivity sensors are utilised. It is initially pre-set to a value of 20.

The adjustable Delay value (1-255) is used to prevent re-triggering from a single hit on an input. It is initially pre-set to a value of 5 mS.

The unit  will operate as shown  for the General MIDI drum map. Other drum maps can be used. If a different drum value is required, at any time, then the programming procedure can be repeated.

Normal Mode:

In Normal mode the drum inputs are scanned and the corresponding MIDI note on/off data is transmitted on MIDI channel 10. The MIDI drum range choice is from 0 to 127 as shown in table 1. However the actual drum range and sound depends on the MIDI sound module. 

The General MIDI (GM) drum specification has drum values from 34 to 80.  If the Menu switch is pressed then the unit enters programme mode.

Circuit further explanation:

• Explanation of the circuit schematic

The schematic is available in GIF format:

• Midi 8-Way Drum Pads Schematic