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.
The Minitor III, IV, and V two-tone pagers are computer programmable. The software is available from 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.
A common questions is whether you can use a Motorola RIB to program the pagers. The short answer is no. Motorola radios use a data bus to talk to the RIB, where the transmit and received data share the same wire. The pagers use separate TX and RX lines. Luckily, this makes the programming circuitry easier, even though you can't use a RIB for both pagers and radios.
The programmer shown here is basically a stripped down version of the Motorola 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.
In reality, all that is needed is an RS-232 to TTL level converter. These can be bought online dirt cheap if you'd rather buy one than make your own. Here are a few places to look:
Or, if you prefer USB, check this one out:
An advantage of USB is that power to the converter is provided by the USB port so you don't have to wire up any additional power supply. Just make sure you install the drivers for the USB cable and select the correct COM port in the programming software.
If you want to build your own, read on. A schematic of my 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)
Part Description All Electronics Part #
U1 MAX232 SP232ACP
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.
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 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.
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.
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!
The Minitor V charger can also be modified for use as a programming cradle, although it requires a little more care. Unlike the Minitor III/IV cradle, the Minitor V cradle has pads on the printed circuit board (PCB) that make contact with small springs that support the pins that in turn make contact with the pager. The charging cradle is populated with the pins necesary for charging the battery and does not include any extra pins. However, there is another set of pins used for charging a spare battery. These pins are longer, but can be cut down to fit the main cradle if you don't need the spare battery charging slot.
The two pictures below show both sides of the charger circuit board and the arrangement of the pins in the charger before modification.
The picture below shows the modifications that will need to be made to the circuit board to accommodate the two new pins needed for programming. The circuit board trace going from D26 to one of the existing pads will need to be cut in three places with a razor knife. A jumper wire will then need to be installed to take the place of the circuit board trace that has been cut. The remaining portions of the circuit board trace will need to be ground very carefully to expose the copper underneath the solder mask. Be careful not to remove the copper from the PCB. A small area on the ground plane of the circuit board can also be exposed for connection of a ground wire for the programming circuit. Finally, wires will need to be soldered to the two new "pads" that have been created for the programming pins.
The picture below shows the circuit board after modification.
The picture below shows the modifications to the rear "spare battery" pin for placement in the main portion of the charging cradle.
The picture below shows the underside of the cradle after adding the two extra pins for programming.
See this forum thread for some different ways people have used the same basic ideas to create their own programming cradles.
For troubleshooting tips, see the Radio Programming Interface page.