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DTMF-ENC232 is a DTMF (dual tone multiple frequency) encoder board that is controlled via 9600 baud RS-232 serial commands.  By using a terminal program such as HyperTerminal or custom developed software, an attached radio transmitter can be keyed with continuous or momentary DTMF digits being sent at any interval.  Example applications include the remote controlling of complicated repeater controllers and the driving of DTMF relay camera pan / tilt systems.


  • Dimensions: 3.93" x 3" x .4"
  • Weight: 1.4 oz.
  • Input voltage: 8.0 to 14.0 volts DC (37 ma max)
  • Operating temperature: 0 C to +70 C
  • RS-232 serial input: 9600 baud, 8 data bits, 1 stop bit, inverted data
  • Output level: 100 mv p-p to 1.9 v p-p (400mv default)
  • DTMF digits: 0123456789ABCD*#
  • Single DTMF digit duration (100 ms on / 50 ms off)

  • RS-232 Commands:

    Pad Description
    1 Serial out (female DB-9 pin 2) to PC
    2 Serial ground (female DB-9 pin 5) to PC
    3 Serial in (female DB-9 pin 3) from PC
    4 Push-to-talk (pull to ground) to radio
    5 Audio ground to radio
    6 Audio out to radio
    7 DC ground from power supply
    8 DC in from power supply


    Pot Description
    VR1 Adjusts audio output level (clockwise to increase)

    LED Description:

    LED Color Description
    D12 Green Power applied to board
    D10 Yellow DTMF tone is being sent
    D11 Red Push-to-talk enabled (radio transmitter on)


    Description Parameter(s) (ASCII)
    v Verify communication link with DTMF-ENC232 None
    t Turn radio transmitter off/on 0=off, 1=on
    d Send DTMF digit for 100 ms 0123456789#*abcd
    c Send continuous DTMF digit 0123456789#*abcd
    p Send continuous single pure tone c1,c2,c3,c4,r1,r2,r3,r4 (see table below)
    s Stop sending continuous DTMF digit or single pure tone None

    Example set of commands:

    t1 turns the radio transmitter on, d# sends the pound DTMF digit, t0 turns turns the radio transmitter off.

    Return Values (after command sent):

    (Every command will return a success or failure response.)

    Return Value (ASCII) Description
    ok <cr><lf> Success on command sent
    ? <cr><lf> Failure on command sent

    Single Pure Tones:

    (Single pure tones can be used for diagnostic purposes.)

    c1 1209 Hz
    c2 1336 Hz
    c3 1477 Hz
    c4 1633 Hz
    r1 697 Hz
    r2 770 Hz
    r3 852 Hz
    r4 941 Hz

    Trouble Shooting Tips:

    Problem Solution
    Green LED off (won’t power up)
  • Verify input voltage (8 - 14 VDC)
  • Verify input voltage polarity correct
  • Output tones distorted
  • Verify input voltage (8 - 14 VDC)
  • Failure to communicate with DTMF-ENC232
  • Verify PC RS-232 protocol set to 9600, n, 8, 1
  • Difficult controlling remote device
  • Adjust audio output level via the VR1 pot

    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.