The TDD-8X Commercial DTMF Decoder, MoTron's original DTMF Display Decoder, is a fully assembled and tested printed circuit board. The TDD-8X decodes all 16 DTMF digits--standard telephone touch-tone signals 0-9, * and # and the A,B,C and D digits generated by communications radios--and features a large, easy to read, 8-digit red 7-segment LED display. The eight digit display, 96 character memory and left-right scroll functions allow the user to capture, store and display up to 104 characters without loss of information. A reset button clears both the display and memory, and resets the microcontroller.

The TDD-8X must be directly connected to the audio source, and requires an audio level between .1 and 6Vpp (speaker-level audio). Please Note: The TDD-8X cannot decode line-level (microphone) audio. Both sides of the audio input have DC blocking capacitors that allow the audio signal to pass while blocking DC. If you intend to install the TDD-8X on a phone line, it is best to use an FCC part 68 approved coupling device. The TDD-8X will decode tones from a tape recording if the recording is of reasonable quality. The recording should be made using a direct electrical connection to the tone source. Recordings made by placing a microphone next to a speaker and recording "through the air" will generally be too distorted to be decoded.

As each digit is decoded, it is displayed on the far right-hand LED. The previously decoded digits, if any, will shift to the left. The digits are placed in memory as they scroll off of the display. The "off screen" memory will store up to 96 characters, and can be viewed using the scroll buttons located below the display. The scroll right button will shift the characters one digit to the right each time it is pressed. The scroll left button will move the characters back to the left until the last digit decoded is displayed in the far right hand LED. Decoding a new digit will restore a scrolled display, placing the new digit in the correct sequence, and preventing data from being overwritten.

Since 7-segment displays are being used, special characters must be used to represent the touch-tone digits * and #. The A, B, C and D digits are also decoded and displayed. Refer to the chart in Figure 1.

When the TDD-8X leaves the factory, it is set up to decode touch-tone digits as fast as 12.5 characters per second (cps). This represents a tone length of 40 ms with a spacing of 40 ms. Most fast auto-dialers send at a rate of 10 digits per second, or 50 ms tone/space. Therefore, the TDD-8X should decode almost any fast auto-dialer on the market today.

The TDD-8X is a stand-alone device--a computer is not required for operation. However, as each digit is decoded and displayed, the ASCII equivalent is transmitted on the serial port. This output can be connected to a computer, or serial printer, for automatic logging or remote data entry. The serial output does not make the full swing in voltage as per RS-232C specifications. However, most computers will accept and correctly "read" the serial data. The TDD-8X uses a mini-phono jack, marked "SER", for serial data output. The required custom computer cable is available, as well as cable drawings in the manual if you prefer to assemble your own.

The TDD-8X requires a minimum of 9 VDC @ 200ma of current. The board will operate cooler at the lower voltage. However, if the TDD-8X is to be connected to a computer, a 12 VDC supply may be necessary; the ASCII output "swing" is dependent upon the unregulated voltage input and many older computers will not recognize the lower TTL levels. The center pin of the power jack is positive. The board is reverse polarity protected so no damage will result if power connections are accidently reversed.

Our Tonelog IBM/Compatible software (DOS) captures the date and time along with the decoded digits, and writes the information to an ASCII text file. Tonelog for Windows, released July 24, 1996, incoporates the same features of the original Tonelog into a Windows application. Tonelog for Windows is a 16-bit program that will run in either Windows 3.1 or Windows 95. Both Tonelog and Tonelog for Windows are automatically shipped with the TDD-8X.

Since we released the first TDD-8, back in June '91, we have had many request for an enclosed decoder, with a variety of other features. If you need or prefer an enclosed, portable decoder, look into our Tone-Master TM-16a and TM-16a Plus.