Build Your Own Motorola Minitor III/IV/V Pager Programmer and Programming Stand
This article describes how to build an inexpensive programmer and programming stand for the Motorola Minitor III and Minitor IV pagers. I've also included information about the Minitor V, although I don't have any first hand experience with this pager quite yet.
Background
The Minitor III, IV, and V two-tone pagers are computer programmable. The software is available form Motorola (software for the III and IV costs money, but the software for the V is available for free download from the Motorola website), and they also sell a Universal Programming Interface (UPI) and programming cradle. The UPI costs about $230 and the programming stand (cradle) costs about $100. You can build your own programmer and modify a standard charger to act as the programming stand. Total cost is less than $20.
The Programmer
The programmer shown here is basically a stripped down version of the UPI. A schematic of the full UPI is available at www.batlabs.com if you want to build the “full” version. My version doesn’t include the comparator circuit or 1.5V power supply, neither of which is necessary.
A schematic of the programmer is below. The circuit uses a MAX232 IC, which converts the +/- 12V RS232 signals from your computer to 0-5V TTL signals that the pager uses. A 9V battery powers the circuit, so a 78L05 voltage regulator is used to drop the voltage down to 5 volts. Resistor R1 and the LED just indicate that the circuit is powered, and could be removed if desired. Resistor R2 is used for programming some types of two-way radios (in conjunction with an external diode in the programming cable) and can be removed if desired.
Programmer Schematic (click to enlarge)
Parts List
Part Description All Electronics Part #
U1 MAX232 SP232ACP
U2 LM7805 7805T
C1,C2,C3,C4 10uF electrolytic capacitor 10/16VR
R1 1k ohm resistor 1K-1/4
R2 10k ohm resistor 10K-1/4
D1 LED LED-2
P1 DB9 Connector DB-9S and DB-9H
J1 Stereo Jack MJW-20
S1 SPST SwitchMTS-4PC
I used a 3.5mm stereo jack for the connector on the “pager” side of the interface, since it’s a readily available and inexpensive 3-conductor connector. I built the circuit on a prototyping PC board available at RadioShack. A few pictures of the completed programmer are shown below for reference.
Front View
Rear View
Inside View
Pager Interface
Note: If you already have a programming cradle and want to use it (instead of homebrewing your own), here is the schematic for a cable that can be used to interface this programmer with the Mintor III/IV/V programming cradles:
If, on the other hand, you want to roll your own programing cradle, here is some info that may be of use to you:
This is the pinout of the Minitor III/IV pagers when in programming mode:
This is the pinout of the Minitor III/IV pagers when they are NOT in programming mode, for reference:
This is the pinout of the Minitor V pager when in programming mode:
Note that some of the pins have different functions when not in programming mode. To put the pager into programming mode, shut the pager off and turn the channel selector to “C”. Then, turn the pager on while holding down the squelch button. The pager will emit a loud, long BEEEEEEEP. To indicate that it is now in programming mode.
The Minitor III/IV Programming Stand (Cradle)
The programming circuit has to interface with the contacts on the bottom of the pager somehow. My first attempt at a programming stand consisted of some bent pieces of wire screwed into a chunk of 2x4. The wires were formed so that they would touch the appropriate contacts on the bottom of the pager when the pager was held on the wires. See the picture below.
While this system worked, it certainly wasn’t elegant or professional, and was inconvenient because I had to hold the pager on the wires during programming. I wanted a cradle I could drop the pager into and not have to hold on to during programming. I decided to modify my pager’s charger to accomplish the task. The charger only comes with two contact pins…power and ground. However, there are holes in the charger base where the other pins should be. All I needed to do was add two more pins (TX data and RX data) in the appropriate locations and I would be in business.
Since the charging stand didn’t come with any extra pins, I had to find my own. If you have an extra, unused charging stand you could steal the pins from that stand. I didn’t have an extra charger, so I didn’t have extra pins. Instead, I modified some pins found in Deutsch connectors. A small screw could probably also be used. I just used what I had available. The pictures below show the pin before modification, and after modification next to a Motorola pin.
Original Pin
Modified Pin (left) and Motorola Pin (right)
The pins are held in place in the charger base by pieces of metal that act as springs. Luckily, the charging stand had two unused springs, so I wouldn’t have to make any. I just had to modify the two unused springs and move them to the locations I wanted. This involved cutting away part of the PC board and soldering the springs into new locations. Unfortunately I forgot to take a picture of the charger before modification. A couple pictures of the modified charging stand are below.
A standard audio cable with 3.5mm stereo plugs on each end is used to connect the programmer to the cradle. Other connection schemes are certainly possible…that’s just what I decided to use. Happy programming!
Minitor V Programming Notes
While I don't have a Minitor V to play around with quite yet, I'm sure that a similar modification could be done to its charging stand to turn it into a programmer.
One of the caveats with the M5 is that the circuit as shown can only be used for normal programming, not for firmware updates. Thanks to these pictures from ffexpCP, though, it's easy to figure out how to do the firmware updates. These pictures are the "guts" of a Minitor V programming stand.
Top View
Bottom View
As you can see, this is a very simple device! These pictures show that if you want to flash new firmware onto the M5, all you have to do is apply 5VDC to the pager's power pin. If you build the programmer described above, you already have the +5VDC! Apply to the correct pin (see the pinout above) and you're in business. Happy programming!
Hints and Troubleshooting
For troubleshooting tips, see the Radio Programming Interface page.