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DTMF-4HC is an inexpensive, self contained, DTMF decoder or touch tone decoder board which permits users to control remotely, via radio or other audio producing source, the on or off state of four high current devices. For larger applications several DTMF-4HC DTMF decoder boards can be attached to the same control audio source to control dozens of devices. DTMF-4HC supports four modes of operation. These mode settings control how the DTMF-4HC behaves. Password support is also available for increased protection from unauthorized entry. All information is stored in non-volatile eeprom memory.



  • Dimensions: 4 3/4" x 2 5/8" x 9/16"
  • Weight: 2.2 oz.
  • Input voltage: 12.0 to 14.0 volts DC (15ma idle, +25ma per energized relay)
  • Operating temperature: -10 C to +70 C
  • Microprocessor: Microchip PIC16F627-20/P (4 MHz)
  • DTMF / Touch Tone receiver: Motorola MC145436AP
  • Audio input impedance: 100K Ohms
  • Audio input level: .1v to 5.0v peak to peak
  • Relay driver: ULN2803 (open collector outputs 500ma max. each)
  • Relays: Omron G6C-2114P (sealed)
  • Relay contact rating: 8 amps @ 12 volts DC / 250 volts AC
  • Relay contact life: 5,000,000 operations
  • Modes: 4
  • Factory default mode: Mode 1, no password
  • Password length: 0 to 9 digits
  • Valid password digits: 0123456789ABC*#

  • DTMF-4HC modes of operation:

    Mode 1: All four relays are latched.
    Program mode: Press 1.Relays are turned on (*) or off (#) and remain in that state.e.g. 4* turns on relay 4, 4# turns the relay 4 off.
    Mode 2: All four relays are momentary.
    Program mode: Press 2.The relay is in the on state while the corresponding DTMF tone is being received and in the off state when the DTMF tone is absent. This is useful for controlling devices like pan and tilt cameras.e.g. While 3 is being pressed relay 3 is on.
    Mode 3: Mix of mode 1 and mode 2.
    Program mode: Press 3 followed by the number of relays to be latched (1-3). The remaining relays are momentary.e.g. After the user programs 3 for this mode and enters 2 then relays 1 and 2 are latched (like in mode 1), and relays 3-4 are momentary (like in mode 2).
    Mode 4: All four relays are latched and mutually exclusive.
    Program mode: Press 4 followed by the relay number that will turn on by default whenever the DTMF-4HC DTMF decoder is powered up (1-4). This mode is for simplified control of latched relays (no need for * or #). The relays are mutually exclusive which means only one of the four relays will be on. An example application for this is video camera switching where only one source can be selected at a time.e.g. Pressing 4 turns on relay 4. Then pressing 1 turns off relay 4 and turns on relay 1.


    Multiple DTMF-4HC's:

    The DTMF-4HC DTMF decoder is designed to control four devices (via relays) but it is possible to control more devices by attaching multiple boards to the same incoming audio source and setting a password (more of a board ID in this case) for each board.

    Warranty & Service:

    If the product fails to perform as described in our product description or specification, within 90 days from the date of shipment to the buyer, we will repair or replace the product and/or accessories originally supplied. Failure due to improper installation, misuse, abuse or accident is not covered by this warranty. Incidental and consequential damages are not covered by this warranty. The buyer must obtain a Return Material Authorization by calling (248) 588-4400, and shipping the defective product to Intuitive Circuits, 3928 Wardlow Ct.,  Troy, MI 48083, freight prepaid. After the warranty expires, we will promptly supply an estimate for the repair cost.