First of all, I am not even a noob when it comes to electronics. I don't even know what I am asking is possible but here it comes.

At first glance, it may seem as an computer-related question, but please bear with me.

One of my friends brought me an old-school Casio SF-8000 today. Device looks like this:

enter image description here

Surprisingly, device is still working but it seems that connection between the keyboard unit and screen begin to wear out, so screen is flickering and about to throw the tovel. He asked me if it is possible to transfer the data from device to PC. It has about 700 address + phone records in it, so doing the hard work manually with keyboard is not really a feasible option.

I looked up the net for a suitable cable. It seems what I need is a cable with 2.5 mm stereo jack in one and and a 9-pin DB9 (serial) cable in the other.

I also found a layout diagram to see which pin on one end should be connected in the other hand.

enter image description here

And here is a layout of the DB9 port pins.

enter image description here

"Easy enough" I thought.

I was about to order the cables to cannibalize them, but then I found this url:


What it says really broke my heart:

Most Casio digital diary models have a small serial port on the side where you can connect a serial cable to exchange data with a PC (or Mac or whatever). The serial port accepts either a 2.5mm plug or a 3.5mm plug, depending on which model you have. Do not try to adapt one plug size to the other - the 2.5mm port operates at 6 volts, while the 3.5mm port operates at 12 volts. Do not try to wire your PC serial port directly to the diary port without the proper cable electronics - this will damage your diary. Do not experiment with cables intended for other devices which happen to have a similar 2.5mm plug! There is no standard, and most of these cables are wired differently from the Casio diary cable. Not only will they not work, they might damage your diary.

It seems serial interface of a regular pc works in 12 volts, whereas my device needs 6 volts to operate in the interface.

In same page, there is a link which contains cable diagrams. It says that I need a Maxim MAX233A or MAX232A chip to drop the voltage to required levels. I looked up to the local webstores but it seems no retailer has this kind of chip in their offer. I called the official importer but it seems they are not keeping stock and only importing in big quantities to electronic producers.

So my question is (noob alert): can I use some kind of resistor or something else to regulate the voltage to 6 volts? Or a chip is the only way to go? Apparently, I am not able to find the speficic Maxim MAX233A chip in my locals, but there should be some other chip that can do the same job. So what should I look for and how should I ask it when I go to an electronics store?

I am capable of doing simple soldering and producing makeshift cables, but I have no idea how to convert this voltage.

Thanks for your patience and your answers in advance.

UPDATE - This is how I solved it

Thanks to the tips provided by JRE, I decided to pay more attention to the IMSLsoft's page. It says there are usb dongles which acts as serial ports, utilizing the FTDI TTL-32R chips. Page said:

You can now buy a ready-made USB-serial cable that includes the voltage step-down circuit needed for the older Casio models: FTDI - TTL-232R-WE - CABLE, USB-TTL SER CONV 5V, WIRE END. Needs only the 2.5mm plug to be added to connect your Casio diary to a USB port.

Ordering something abroad was going to be my last resort, so I started to look a similar dongle being sold in Turkey. Fortunately I found one utilizing the same chip, looking like this:

USB dongle with FTDI chip

I soldered (ok, frankly speaking, I did not soldered, I just wrapped the naked cables to the pins and taped them. Shame on me.) the cables to the pins and decided to give it a go.

Unfortunately, I forgot to take photos of finished product, but it was not worth seeing anyway :) I just connected the wires to the pins of the dongle.

I used the driver from FTDI website for the relevant chip.

I opened up the demo application of IMSLsoft's XLink/Win. I was going to order the full version if demo worked OK (demo only transfers a small amount -20 or so- of the records from the device).

I fired it up, but it keep giving "unexpected character" errors and showing the received hex codes from the device. I converted the hex codes to ASCII, it was saying "NON GENUINE DEVICE DETECTED" over and over, until transmission gets stopped by software.

I figured this should be caused from the driver, since neither Casio device nor the software performs any genuinity check.

I switched to my fellow friend Ubuntu (normally I use OS-X) and installed a graphical software which captures the serial port data (you can use any software reads data from serial. Fortunately, ubuntu recognised the dongle and COM port was visible in software.

There was one last problem for transmission: Apparently, casio device expects some kind of confirmation from computer side in order to begin and continue the transfer, so device was not sending any information.

I used the serial print option of the device, and there it was, all info just flowed through the cable to my screen! I was so happy so I have moonwalked in middle of the office, but only a little.

Hope this helps to someone who needs to go through a similar journey :)

Thanks a lot to everyone who tried to help.

  • \$\begingroup\$ Just FYI, the official Maxim website is maximintegrated.com and factory sells direct to individuals. I just checked and MAX233ACPP is currently in stock. For only 1 piece just request a free sample. (You don't mention your country; we must comply with USA DoC export control laws, but I don't think MAX232 is restricted for export.) \$\endgroup\$
    – MarkU
    Sep 15, 2015 at 1:43

2 Answers 2


The page you linked to (http://www.imslsoft.com/cable.htm) includes tips on how to build the cables. There is mention of the Max233, but there are other possibilities as well.

For the 2.5mm, there is a dead link but the Waybackmachine has a copy: 2.5mm Casio serial cable at the Waybackmachine. In fact, all of the Casio stuff seems to be pretty outdated with loads of dead links - the Waybackmachine is really your friend.

You apparently aren't the first to have problems with the Casio devices. Fortunately, a lot of people put their efforts on the Internet where it can be found.

This page says that your SF8000 uses the same cable as a metric crap load of other Casio devices. The (fuzzy) picture of the adapter also gives a US patent number, which leads to this patent which includes a circuit diagram of the adapter, and which matches the one that that I linked to from the Waybackmachine.

In your place, I'd use the Waybackmachine link since it includes some notes on the parts and values used. In general, all the parts look like garden variety parts you should be able to order from any supply house.

More info that you can only get from the Waybackmachine. Includes more tips on the FET and D1.

For completeness, here's the circuit diagram from the patent: enter image description here

  • \$\begingroup\$ Man, I really forgot the waybackmachine. I must be getting old. Thanks a lot for this, it will probably be sufficent. I really appreciate it :) Oh, by the way, I already contacted the pccables but they told me that unit is no longer in production. \$\endgroup\$ Sep 14, 2015 at 14:30
  • \$\begingroup\$ Just a question: as I said, I really don't know anything about electronics and I'll probably take this drawing to a professional but, is there any chip or other integrated circuit parts required for this? \$\endgroup\$ Sep 14, 2015 at 14:34
  • \$\begingroup\$ No integrated circuits at all. There's one plain old NPN switching transistor, two zener diodes (careful: different voltages!) one FET (field effect transistor) and a handful of resistors. If you are careful, you should be able to squeeze it all into the shell of the DB9 connector. Also, take a look at the link I just added. \$\endgroup\$
    – JRE
    Sep 14, 2015 at 14:41
  • \$\begingroup\$ You encouraged me a lot, maybe I just should plug in my soldering iron and give it a go :) I don't want to turn this into an electronics 101 class but just curious about one more thing: how can one tell what kind of resistor should be used just by looking at the drawing? It seems it has numbered resistors, are they the types of resistors? \$\endgroup\$ Sep 14, 2015 at 14:48
  • \$\begingroup\$ The numbers are just for reference, so you can say R1 instead of "the resistor connected to pin 2 of the DB25." The text here: web.archive.org/web/20060116090703/http://pfranc.com/pclink/… and here: web.archive.org/web/20000831023622/http://… tell you what values to use. \$\endgroup\$
    – JRE
    Sep 14, 2015 at 14:51

Resistor dividers would work for going from 12 V output to 6 V input, but then you run into an issue going from 6 V output to 12 V input.

I've linked to a search for MAX232A on digikey. It's showing MAX232A that are in stock and in PDIP package type. I figured that'd be easier to solder to than surface mount. Probably be easier to use a breadboard anyways though.

  • \$\begingroup\$ Thanks a lot, I'll use JRE's diagram first and if it fails, I will use this one. Abroad shipments can take waaay to much time so I must probably order one right now anyway :) Thanks again. \$\endgroup\$ Sep 14, 2015 at 14:32
  • \$\begingroup\$ I think you can get those from local stores - those are must-haves for a lot of different circuits. I have a few in stock - actually one of them is even taken out of a circuit board and I have the charge pump caps permanently soldered to the pins \$\endgroup\$ Sep 14, 2015 at 15:27

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