HP Forums

Full Version: WP 34S - best cable layout ?
You're currently viewing a stripped down version of our content. View the full version with proper formatting.

I'm currently trying to build my own WP34S from a HP30b (my own usage, and challenge !).
I've seen many types of circuit layouts to build a cable to flash with the new firmware but what is the best one ?
Also, some have only an "erase button" whereas others have "Erase + Reset buttons": what is strictly sufficient ?

Thanks !
I am curious as well. Considering the vast amount of people that are WP-34S fans, there is general no information on the cables. I found a pinout of the board, and a pin pitch. But other than that. I can tell that the erase button is optional for sure as you can jump that with Vcc with batteries in to erase the unit.

The thing I am unclear on is whether the reset is required, and if the TX/RS are tied together or not for full/half duplex.

Would love to see more information
Also found these two threads:

What I can gather is the we have to ensure the Serial to TTL is not using 5V for sure for Vcc, and that the TX/RX lines are also 0-3.3v rather than 0-5v. Everything else appears to be optional.
Someone in a fb group recently said they successfully used the following:



Instructions (combination):



Note, I haven't tried the above. I recently acquired the original serial cable but haven't flashed a calculator yet as I'm waiting until the overlays are available again.

Good luck!
(01-28-2021 04:26 AM)dmh Wrote: [ -> ]Someone in a fb group recently said they successfully used the following:

I originally did it numerous times the "Theremin guy Newegg cable way", but someone has since given (!) me the "official" cable. The homebrew Theremin guy way with the Newegg cable worked fine, but is a little fiddly holding the probes by hand to the pads. So it might take a few tries to get it to flash. But it gets the job done and the price is right!

The good news is that at this point, the WP34s firmware level is VERY stable, so it's not likely you will need to reflash soon or often. They are only doing the very rare bug correction now.

So, while the official cable is a little easier, the end result is exactly the same. Unless you are making a ton of these, I wouldn't spend large $ on an official cable (if you can even find one).
You don't need either erase or reset buttons!
With the Newegg cable,
RESET is achieved by poking the reset switch on the calculator (via a little hole on the back with a paper clip).
ERASE is one of the pins (bottom left) of the 6 on the calc's flashing pad. Jumpering 3V (from either top right pad which is 3V or one of the coin cell's +terminals) to this pad executes erase.
(01-26-2021 01:34 PM)rallyrabbit Wrote: [ -> ]Also found these two threads:
This link doesn't apply unless you have one of the Harald boards installed. Those are not required, but permitted flashing via USB.

What I can gather is the we have to ensure the Serial to TTL is not using 5V for sure for Vcc, and that the TX/RX lines are also 0-3.3v rather than 0-5v. Everything else appears to be optional.

Just do it like the Theremin guy did. The two 3V coin cells on the calculator are in parallel (for longer battery life). Remove one of the cells. Install a fresh one on the other side (you don't want low volts when flashing).

Here are some notes I took (or probably copied from his original web page):

"The two coin batteries are actually wired in parallel, so I just pulled one out to get at +3V and ground. The then exposed center battery conductor is ground, the rim conductor (located above the center connector, up inside the housing) is +3V.

You have to erase the firmware, then program it with the serial cable. Erasing is performed by power cycling and resetting the calculator with the lower left serial port hole connected to +3V (there is a small "reset" hole with a switch behind it located directly above the serial port).

Those are 1k resistors in series with the serial leads to limit current just in case (battery voltage is ~3V, the TTL TX level is ~3.3V). On the serial port: green=TX (data into the calc), white=RX (data out of the calc), red=+5V (unused for this project), black=ground (common for TX & RX).

Serial programming took all of maybe 20 seconds, and it's not too hard to keep the connections steady for that long, even hand-held as in the picture. If you botch the programming just start over, I don't think there is much - if any - risk of bricking it. Don't leave the batteries in it unprogrammed, otherwise they might get quickly drained."

Me back again. Please note once more: The red wire in the cable is not needed for either the erase procedure OR the actual reflash. You don't use it. Just follow the picture on the ThereminWorld archive page where he is holding the resistor leads to the TX and RX pads and the black wire (ground) is hooked to the ground terminal from the removed coin cell. I don't think you actually need to use the +3V from the open coin cell socket because that is only used to trigger the ERASE and there is a pad supplying 3V.

Wire Summary:
Red: not used
Green: TX -- hold to top left flash pad through a 1KΩ current limiting resistor
White: RX -- hold to top middle flash pad through a 1KΩ current limiting resistor
Black: alligator clip to the ground terminal (in center...looks like a 3-pointed spur) of open coin cell cavity

Attached is a schematic of the flashing pins on the back of the calculator and a flashing sequence. This I didn't create, merely screenshotted off the original ThereminWorld site a few years ago and saved in my records. It seems to now be missing in the archive of the ThereminWorld page, which is a pity.
Depends on how you define "best". Are you looking for cheap, bells and whistles, or reliability?

For reference, here's the 20b/30b cable guide.

For hardware I recommend Harald's board, described here.

For a connecting cable, if you're concerned about reliability, I made this connector that doesn't require any soldering on the plug end.

Reference URL's