EFJ 5100 Case Swapping: The Great Cheat of EFJ #3

Does this radio look familiar? It might. Just earlier today, it was inside the same case pictured in my first EFJ 5100 article.


What changed, you ask?

Well, it now has a full keypad.

Well what is so cool about the full keypad?

It just so happens that I’ve been experimenting with various repeaters. These include the Argent Data Systems ADS-SR1 simplex repeater as well as the Motorola SM120 repeater with i50r basic autopatch controller (more on that particular model to come). These units are basic repeaters which retransmit your signal at a higher power or from a different location. Simplex repeaters record your transmission and then retransmit it (usually on the same frequency) after the completion. The Duplex repeater simultaneously re-transmits your signal on a different frequency.

However, both of these controllers require DTMF tones to control them (and it just so happens that I’m using UHF frequencies for these units). The ADS-SR1 uses DTMF to control functions like enable/disable of the repeater, the “say-again” functionality etc. The Motorola i50r controller requires it for phone patch actuation and for dialing on the phone line (as it allows full access to a connected phone line. pretty cool :)).

Well how the hell did that modification happen?

EF Johnson (and Motorola etc) sell their radios in three versions:

  1. Model 1 has no screen or controls: just the selector knobs on top and the buttons on the left. The only indication is through the speaker and the blinking LED which has multiple colors.
  2. Model 2 has a “limited keypad” and a display. Function keys exist (four of them) which can be reprogrammed at will using PC Configure.
  3. Model 3 has a “full keypad” and display, which basically means it has number keys. They can be used to type in text for entering channel aliases on Front Panel Programming, as well as for sending DTMF dial tones over the air for calling phones or controlling devices remotely

Basically, I had a Model 2 UHF (380-470 mHz) and a Model 3 900 MHz rig. A forum post alerted me to this possibility and I was curious. Could it be that EF Johnson User Interface boards all have the DTMF key contacts?

The answer is apparently yes. If you pop open a Model 2 UHF, the board which is closest to the front and contains the display and key contacts has all 12 DTMF key contacts on them. It even has an unused rubber pad where the DTMF keys are.

How do these keys work?

For those unfamiliar, these keys and the similar ones in most cell phones operate fairly simply. Two copper traces on the PCB are laid out in circular patterns. They don’t touch, but they’re quite close to each other. A rubber keypad is created which has a conductive surface on the back. When this is depressed, it comes into contact with the PCB, making a connection between the two lines (one could be ground and the other could be a line to a microprocessor with a pull up resistor). When this gets pulled low, the processor recognizes that a key is depressed (depending of course on your architecture, it could be through Hardware controlled or polled I/O or generate an interrupt request…just proving that I’ve taken EE 14…).

So do I feel cheated?

Yes. Yes I do. But the good news is that all of my Model IIs can be upgraded by case swapping. Unfortunately, that means you need a good case to swap out. I had a 900 unit left over from my most recent programming expedition and I used that case as it was in good condition (but of the 20 units I possessed, that was the only one that looked acceptable).

EDIT: Yes I did have to modify the OPT file to allow full keypad. Conveniently, when I enabled FPP and MDC 1200 the full keypad was already enabled, so I didn’t need to futz with it any more.

4 thoughts on “EFJ 5100 Case Swapping: The Great Cheat of EFJ #3”

  1. I done the case swap a couple of weeks ago and it was a really good way of updating a cheap UHF 5100 to a full keypad version. When I first swapped the old case for the new I thought it would work straight away. Had to hexedit the OBT to enable the full keypad which took me a couple of hours. One mod will enale p25 and take away full keypad, just keep changing values and I eventually got what I wanted.

    Cheers Harrold

    1. The easiest way turns out to be obtaining a copy of the EFJ internal program to adjust the options enabled.

      But in principle, the option file’s encoding doesn’t have any checksum to verify it hasn’t been altered. Using a simple hex editor, you can simply alter it and try it out by loading it into the radio. Continue twiddling bits until the options you want magically appear.

      1. I have taken a little bit of time to play with HEX editing and it’s doable but tedious with a capital T! I have heard of such a miraculous software package, but have never found the same in the wild. Suggestions for locating it are welcome!

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