WP34s Programming Cable

[Jonathan Cameron]

I got my WP-34s programming cable working. I used the "USB to TTL Serial Cable Adapter FTDI Chipset PL2303HX Cable Computer Cable" mentioned in these posts (dewstar) and shown by Theramin on his page (http://www.thereminworld.com/Forums/T/29...b-to-wp34s).

I ordered switches, etc, and did not get exactly what I wanted but it ended up working okay. Here is a my circuit diagram, which illustrates exactly how to connect it (cross TX/RX):



A few notes:

• Since the Erase switch was a push-button toggle switch, I ended up adding an LED so I could tell when the erase was in progress. That makes that part easy: Press the button to toggle "ERASE" on and the LED glows so you can see you are in that mode. No need to hold it down during the process.
• I had thought about including a RESET button, but omitted it since it is pretty easy to use the RESET switch on the calculator.
• I included a DC-DC converter 5->3v because I had orginally planned to have a +3v to supply to the calculator during flashing, but ended up not including it due to some posts that I read. Not sure if it is an issue or not. So I used the DC-DC converter to provide the voltage for the Erase line and to power the LED.
• I included 1K resistors on the TX/RX lines due to suggestions on Theramin's page.
• I probably should have put a resistor on the positive lead of the LED to keep its current at a reasonable level. But it seems to work okay without it. And I'm not keeping it lit for extended periods, anyway.
• Notice that the USB/TTL TX line goes to the Calculator RX (and vice versa). This took a while to figure out. Although several sources said TX to TX, one of the photos in Theramin's page actually shows crossing the lines. That worked, finally.
  

I used a 6-pin 2mm pitch header connector with pogo pins from ebay. The pins go in snugly and do not need soldering. It took a bit of work, but I used aluminium flashing to create the little clip to hold the connecter in place during programming (similar to one by Dave Fredrickson in http://www.hpmuseum.org/forum/thread-183...#post_4013). It is a bit delicate but I have plenty of extra pogo pins so I'll just live with it. Here is my connector without the clip:


Finally, I had some difficulties getting flashing to work after my first flash attempt failed.
i was only able to get this working on windows with MySamba (running as administrator). I could not get the QtFlash working on Windows or Linux.

One thing that helped was in this post: http://www.hpmuseum.org/cgi-sys/cgiwrap/...977#200119
This post has a bit different procedure to reset the calculator to receive a download. This procedure worked for me even after a flash failure (with the calculator looking completely unresponsive):

1. Turn on the calculator (do not worry if it is unresponsive due to earlier flashing failures)
2. Plug in in the programming cable into the calculator and plug the USB end into the computer
3. Set up MySamba to prepare to do the download (do not press [Send File])
4. Press and hold the [On] key
5. Press and hold the ERASE button (or toggle in on in my case)
6. Press the RESET button inside the back cover of the calculator with a paper clip
7. Release the ERASE button
8. Release the calculator [On] button
9. Turn the calculator on (should not get any response)
10. Press the MySamba [Send File] button to send the flash image. After a few seconds you should see the transmit progress.
11. Disconnect the cable on both ends and exit MySamba
12. Press the reset button with a paper clip again
13. Press the calculator [On] button! It should come alive with the new flash image.
    

Next I need to set up a little project box to make it a little prettier.

-Jonathan

P.S. Thanks to many posts here that helped me figure out how to do this!
P.P.S. Edits: updated circuit to include capacitors for DC-DC converter, added assembled picture (below).

P.P.S. Here is the final version, assembled:


The box contains a little perf board with the circuit done with point-to-point soldering. Note the reset tool! As with any first-time project, there are various things I would do differently and better the next time. But this one works and I'll live with it for a while.