This page documents the programmer I designed for flashing the Z-273 module of older model Midland commercial radios. The intended audience for this project is ham radio operators who would like to convert a used commercial transciever to amateur use on amateur frequencies.

I think the key thing to think about when using my programmer is that EPROMs require over 20 volts for programming, but they are otherwise 5 volt devices. The Atmega ("Arduino") microcontroller that runs the show is also a 5 volt device. A USB port can deliver 5 volts, which is fine for reading or verifying an EPROM, but we’ll need another supply for programming it.

While designing and testing and generally messing around to create this board I blew through three or four Atmega chips, so my best recommendation overall is, "Don’t connect the 27V power, except when you actually want to program a chip. Disconnect it when the programming is complete."

The design of the programmer isolates the computer, but if you go poking around and short a 5V pin with the high voltage Vpp pin, you’ll blow your microcontroller as fast as you can blink, and probably your EPROM if it’s connected at the time.

Now that I’ve said that, I did try to protect you in as many ways as possible to prevent screwups caused by plugging or unplugging things wrong or in the wrong order. I put the microcontroller in a socket, so if you can’t resist poking around and you do blow it, you can replace it easily.

Okay, time for directions.

This is the programmer. It connects to the computer via a micro-USB cable at the small blue daughter card in the top left corner.

The center of the board has pins that match a Z-273 radio module. One of the errors in my first prototype board is that the holes weren’t drilled wide enough for the pins to pass through the board (you can see this in the picture), so these headers are surface-mounted. They’re pretty strong, but I’d use a bit of delicacy when removing modules if you have one of my prototypes, just in case. Wiggle, don’t yank.

The top right corner of the card has a couple of loop "test points" for attaching a power pack to supply the programming voltage. When it is time to program new data, you’ll connect 27V to these points. I use three 9-volt batteries wired in series.

The single pushbutton at the bottom edge of the programmer resets the Arduino chip. You’ll need that for loading new sketches to the programmer.

I’ve made use of programs that are readily available on GNU/Linux systems, like Ubuntu. You’ll want to make sure you have all of the necessary tools installed:

You’ll probably need some kind of editor, and you may find it convenient to have an alternate serial communication program. If you use a DOS program to make changes to your EPROM images (DAT files), you may also need DOSBox.

Reading and verifying an image can both be done with only 5 volt power, so no battery pack is needed. Attached your Z-273 module to the header, then plug the USB cable in.

The board will enumerate as a USB serial device, probably /dev/ttyUSB0 (though you can type dmesg in a terminal to check). We can talk to the board either through the Arduino serial monitor or using an alternate serial communication program like minicom.

You’ll need to put your EPROM under a UV lamp for a few minutes to erase it before you can write new data to it.

I’ll cover later how to load new frequency data into the programmer. Basically, you’ll have to compile it into a new Arduino sketch, and use the Arduino environment to upload it to the programmer over the USB cable. For the moment, I’ll assume the Arduino chip has already been programmed.

After you have erased the Z-273 module with a UV lamp, load it into the programmer as before and read the data. Every byte should read as 0xFF, and at the end of the listing you should be told that the module is erased. If it still has some data, it’ll need more time under the UV light.

When it’s time to program new data to the Z-273 module, connect a battery pack to the terminals. The Vpp LED should light up, giving you a visual indicator that high voltage is present. Send a ! to begin burning to the Z-273 module from the data stored in the Arduino sketch. You should see the Prog LED light up as the data is written.

When the write has finished, remove the programming voltage. Then send = to verify that the write was successful, and that it matches the data stored in the Arduino chip.

After you have verified the write, disconnect the USB power and remove the Z-273 module from the header to go back into the radio.

The software that runs the programmer is an Arduino sketch called z273. It both controls the programmer to read and write data to the EPROM and contains a copy of the new data to be burned.

The first time you run the Arduino environment it will create your sketchbook in ~/sketchbook. You should also customize the "board" you’ll be using. Go to Tools/Board and select "Arduino Duemilanove w/ ATmega328." This will set the Arduino to program chips at a speed of 57600 bits per second, which matches the bootloader I use on the chip on the programmer.

Exit the Arduino environment, and unpack my source code from z273.tar.gz.

This should unpack the sketch into your Arduino sketchbook. If you start the Arduino environment again, you should be able to open it with File/Sketchbook/z273

Once the program is open, Ctrl-R should recompile it.

If you plug the programmer into the USB cable, then you can upload a newly compiled sketch by typing Ctrl-U.

The Arduino environment may ask you if you mean to use /dev/ttyUSB0 (or similar) for programming. You do. If it doesn’t ask, then it has probably already figured out what port to use.

Uploading a sketch will require that you press the reset button on your z273 programmer at just the right time. There is only one button on the programmer, and that’s what it is for, so you can’t miss it. I can always get the timing right each time if I do it this way:

If you get an error about the serial port being "not found," in my experience that comes from forgetting that you left minicom open and attached to the port in another window. The Arduino environment cannot upload a sketch while minicom has a "lock" on the serial port. To exit minicom type Ctrl-A Q in the terminal window where it is running.

If you get the timing right, there will be a short delay and then the status line in the Arduino environment will read "Done uploading." If you released the reset button too early or too late you may get synchronization errors, and you’ll just have to try again.

You can also remove the Arduino chip and program it in an Arduino programming card. This works fine; I just think you’ll eventually bend a pin if you remove the chip repeatedly for programming.

All of the frequencies in the program are stored in data.h, and if you inspect that file, you’ll see that it looks strikingly similar to the hex characters we dumped from the Z-273 module earlier. That’s because it is. It is just a little bit of Arduino code wrapped around a hex dump.

This is the only part of the Arduino sketch you should ever have to modify. For convenience, I’ve included a small script called dat2h that will build a new data.h for you from an existing DAT file. If you have new frequencies saved in a file called newfreq.dat, you would update your sketch like this:

Re-open the Arduino environment, recompile the program, and the new sketch will be ready to upload to the programmer (and from there you can instruct it to burn those frequencies into a blank Z-273 module just as before).

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