TOUCH SENSORS

The TOUCH SENSOR circuit allows you to connect conductive elements, especially metal surfaces, directly to the DART controller, making them work like buttons.

 

Touch-sensor settings

  • in this example we start from the DART_EDITOR main screen.
  • The ITEM number 57 has been selected, then the MODE selector has been set to TOUCH-1

The settings-box of the Touch_sensors includes these selectors:

  • MIDI TYPE
    • NOTE, CC, AT, POLY AT
  • DATA BYTE1
    • Value of the message
    • The Data Byte 2 is 0 or 127, depending on the touch_condition.
  • SENSITIVITY
    • ranges from 0 to 127
    • 70 is the default value
  • LED OUT
    • number of the Output pin that will be controlled by the touch sensor.
  • MIDI CHANNEL
    • channel of the outcoming MIDI message.
  • RESET MODE
    • 1 = touch_reset active, 0 = touch_reset disabled.
    • the touch_reset function is related to the Spinner setting, it is basically a pitch-bend lever emulation. The spinner value returns to the selected Reset_Value each time the Touch_Released condition occurs.
    • The return to reset-value is smoothly glided to avoid clicks.
  • RESET VALUE
    • it is the value to wich the Spinner return, on Touch_released condition
    • 64 is the center value that is most commonly used, but it can range from 0 to 127.
  • TOUCH MODE
    • 0 = Capacitive touch sensing. – This is the normal operation of the circuit described above.
    • 1 = Vitual Touch. – When this mode is active, the MIDI signal defined for the touch sensor is sent out relatively to the spinner’s movements: the touch_ON_127 signal is sent immediately at movement start, touch_off_0 signal is sent out when the spinner stops rotating.
    • 2 = Monitoring mode. – when activated, continuous readings of the capacitive sensor can be monitored, so as to establish the sensitivity threshold more precisely.

VIRTUAL-TOUCH examples

In the following videos we have the example of a TOP SPINNER and a SIDE SPINNER that do not use the capacitive touch sensing circuit. in these cases the Virtual-Touch function is used.

The Virtual-Touch sends a MIDI signal with maximum value (127) when the spinner begins to move, then a MIDI signal with minimum value (0) is sent when the spinner stops.
In these videos the DART controllers are connected to the NI Traktor DJ software and the Virtual-Touch signal is mapped to the Traktor PLAY/STOP parameter, so that a scratch turntable can be emulated 😉

Touch sensing circuitry

 

  • the Touch condition is verified by sending a signal from the emitter pin 8 to the receiving pins 7 and 9. the capacitance of the human body is capable of delaying this signal, allowing to determine the Touch_condition_ON and the Touch_condition_OFF.
  • The circuit only requires the use of two 680k resistors.
TOUCH sensing circuit on breadboard TOUCH sensing circuit on DART_MOBO