DTMF Decoder Review

MoTron Tone-Master TM-16A Plus Touch-Tone Decoder

MoTron Electronics 310 Garfield Street, Suite 4 PO Box 2748 Eugene, OR 97402 503-687-2118

Review by Blue Whale

If you're in the market for a small, portable Touch-Tone decoder, forget about Optoelectronics.  For $249, MoTron Electronics will send you a Tone-Master TM-16A Plus, with no questions asked, if you know what I mean...

General Description

The Tone-Master measures approximately 6" by 2.75" by 1", about the size of an AR8000 scanner.  The chassis is metal and feels solid.  The buttons, on the other hand, are of the cheapest plastic variety available, and were probably used to keep the cost low and the circuit board simple (this is unfortunate, as I would have gladly paid more to have solid metal buttons).

Power is supplied from either a 9 volt battery or from its 12 VDC input (the transformer "brick" is sold separately for $10).  Sadly, to install the battery, the chassis must be unscrewed and opened, although once installed the battery does seem to last.  There is a fat (cheap) red LED to indicate power.

Besides the power switch, there are two "Scroll" buttons and a Clear button, the latter being inconveniently placed where all the hand action is, so that it is not uncommon to occasionally hit this button, lose your tones, and then lose your mind.

As I purchased the "Plus" version, my unit also came with an RS-232 female connector for computer interfacing.

Touch-Tones are viewed on a 16-character LCD (not back-lit), and may be simultaneously monitored on the unit's small built-in speaker.  While this speaker is an extremely useful addition, it is unfortunate that the output volume is controlled by a variable potentiometer on the circuit board, which is accessed through a small hole in the chassis.  Besides being difficult to adjust, the potentiometer must be handled gently as its solder joints are the only thing holding it to the circuit board.

The display itself is not particularly clear, and must sometimes be held at awkward angles in order to view the characters (although it is not quite so bad as the illustration might suggest).  In addition, the instruction manual warns that the LCD is sensitive and should be kept out of direct sunlight and away from heat.

Switching on the unit yields:

TM-16a+ READY>

What happens next depends on you.

As a DTMF Decoder

The Tone-Master has a standard 1/8-inch phono jack for its audio input.  As all hand held radios, scanners, tape cassette players, and just about everything else utilizes this same type of jack for audio output, there should be no problem connecting the decoder to whatever the source of your tones are.

What makes the Tone-Master especially useful, however, is that it also comes with a modular telephone line-in jack.  Thus Touch-Tones may be culled from all the various sources that are of interest to hackers.  It is this versatility and attention to detail that makes the unit such a worthwhile purchase.

Actual operation is simple.  All Touch-Tones appear as the characters they are.  For phone operation, the decoder displays a < for off-hook and a > for on-hook detection.  Thus, lifting a phone receiver, hitting all the Touch-Tones, and then hanging up will yield:

<T:123456789*0#>

The T: indicates tones, while a P: indicates pulse dialing.

The decoder uses a - to indicate a seven second pause between Touch-Tones or on-hook detections.  Thus if we had paused midway while dialing our Touch-Tones, the aforementioned example might have looked like this:

<T:123456-T:789*0#>

For scanner operation, the built-in speaker allows you to continue monitoring while you are logging Touch-Tones, although I recommend getting the custom audio out jack option for serious listening.

The decoder can store up to 80 characters in its very volatile memory, which may be accessed via the scroll buttons.

As a Pen Register

This is where the value of the Tone-Master increases exponentially.  A simple RS-232 connection (9600 baud) to any computer running the simplest terminal software will allow the decoder to function as a pen register.  With a computer connection, the unit is no longer restricted by its limited 80-character memory, but by the memory of the computer.

With a simple terminal script, you can easily add time and date functions, or have your computer sound an alarm when certain Touch-Tone sequences are detected.  Both of these features are incorporated in software provided by MoTron Electronics (for MS-DOS machines).

As a Telephone Monitoring Device

For an extra $20, MoTron Electronics will add an audio out jack so that you can pipe your input back out again to headphones, an amplifier, or a recording device.  When the output jack is engaged, the speaker is disengaged, which is another useful feature when you want to mute the speaker without having to deal with the potentiometer volume control.

Conclusion

Despite the cheap buttons, inconvenient battery installation and limited 80-character memory, the Tone-Master is well worth the money.  It is a solid and versatile device that still manages to be small and portable.

Quite simply, there is nothing like it on the market.