WP 34s and USB



#11

Here is a short success story. :-)

I've bought a cable from FTDI, the FT232R 3.3V version. I cut the plug and soldered a 2.5 mm stereo jack on the cable. It looks a bit ugly because I sacrificed a TI cable for it and soldered the wires together.

Now to the calculator. The serial interface used for programming (and hopefully for program exchange in the near future) has connections on the board which are easy to identify. I did not want to solder directly to the tabs of the programming plug because the plug should work as before after modification. The solder points are on the jumpers J5 and J6 just below the big blob. Ground is on one of the battery terminals.

The plug comes from an old "black" TI serial cable (which only works under Windows with a real serial port. I've enough "silver" cables so this one became a donor.) I found a place for the plug under the HP logo. Gluing did not work but it's mechanically a tight fit so I have hopes that it will not break.

I was able to connect to the modified calculator through the cable with SAM-BA which shows that the cable works.

Some pictures follow:

Edited: 24 June 2011, 1:48 p.m.


#12

Nice work!


- Pauli

#13

The connector not only allows the direct connection to a PC via USB (see above) but also the communication between two devices, if they are wired identically. I decided to connect the tip of the plug (calculator side) to RXD and the ring to TXD. If all WP 34S were equipped the same way, a connection cable from Casio will do nicely to make two calculators talk to each other, given I create the software for this. Casio's cable is a cross over connection (tip to ring and vice versa) while the TI cable is wired tip to tip and ring to ring. On the USB jack, the tip is TX and the ring is RX.

With the right software in place, data exchange between the PC and the calculator will be possible with the USB cable. I plan to implement a symmetric protocol that works identically on the PC and on the calculator.

Another thought: HP has wisely decided to bring a bunch of free I/O pins to solder pads on the board. I have the feeling that it wouldn't be too hard to connect an IR transmitter to these pins. This could be used to drive the HP printer. Geoff, we're coming !


#14

Any chance of bit bashing an SD card via the I/O solder pads?
I think this would be more useful than serial -- programs in SD executing from SD...


Pauli


#15

How to squeeze FAT32 at varying sizes into a few KBs of thumb code? You will need a filer then and much more which will easily eat all available space.


#16

Conversely, we could move functions on onto the SD :-)

I would be a lot of work, serial shouldn't be.


- Pauli

#17

Marcus, it's great you were able to identify the proper points in the 30b to connect in a USB port. How did you figure it out? Let's see, USB needs ground, 5VDC, transmit and receive lines. Isn't there a data format for the transfer of valid data using USB? I would think so but I don't know what it is. Did HP included that in their design of the 30b? If so that implies HP has plans to expand their hardware calculator platform. May we all live in interesting times.

Also, I thought USB was designed with a smart computer at one end, as a controller or 'master' and the peripheral or 'slave' that does as it is told. Firewire or IEEE 1394 was designed with smart devices at both ends so they could all work peer-to-peer. Is there enough memory space in a WP-34s to make it smart enough to share data with another 34s?

In my opinion it makes the most sense to have a 34s share info with a PC via USB and use the PC application to move user programs between 34ses. I know it's an extra step to move 'stuff' but it might simplify the initial software implementation.

Just some thoughts,
Gerry


#18

All the smart things are integrated into the "cable" made by FTDI. This cable is, in effect, a tiny controller chip built into the USB plug. So you need the "proper" cable which will cost you around $20. A standard USB cable will not do!

I just made a 1:1 connection of the 3V serial I/O pins inside the calculator to the stereo jack. No magic involved on my side.

Quote:
In my opinion it makes the most sense to have a 34s share info with a PC via USB and use the PC application to move user programs between 34ses. I know it's an extra step to move 'stuff' but it might simplify the initial software implementation.

Both will be possible. I plan to just make the protocols totally symmetric so that it doesn't matter if one of the devices is the emulator running on the PC, making use of the USB or HP's cable, or if it is another 34S.

You will be able to connect:

A/ two 34Ses with a cross over cable,

B/ two 34Ses with two HP cables and a null modem,

C/ a 34S to the emulator via the USB cable as outlined above,

D/ a 34S to the emulator via HP's cable.

Option B works because the HP cable draws its power for the level converter from the calculator, not from the PC serial plug. It's a bad idea to leave the cable connected to the 34S or 20b/30b while not in use because it will drain the battery at a rate of 4mA even with the calculator apparently turned off.

Edited: 28 June 2011, 2:51 a.m.

#19

Hi Gerry,

As far as I can tell, Marcus has "issues" with the mechanical cable connection that HP built into these things. I am pretty sure I have read of his sad, heavy sighs at the nature/position of the pogo connector out the back. :-)

From my quick look at the datasheet, I don't think that the Atmel AT91SAM7L128-EK has a USB port built in. I think Marcus has "just**" connected the existing serial port to a small 3-pin jack out the side of the calculator to make it more convenient. Hence the need for the USB-to-serial cable made by FTDI and the discussion of RXD and TXD in post #3.

BTW, as far as I recall, there actually is a USB-USB specification called On-The-Go (OTG) which will work peer-to-peer. I don't recall much about it but did quickly review the specs a few years ago. I am sure someone here knows a fair bit more about it than I.

Cheers...

** When I say "just" here, I am still somewhat in awe of someone taking their Dremel tool and carving up the case to put this in! :-) Way to go Marcus!!


#20

Quote:
As far as I can tell, Marcus has "issues" with the mechanical cable connection that HP built into these things. I am pretty sure I have read of his sad, heavy sighs at the nature/position of the pogo connector out the back. :-)

Sigh...

Quote:
I think Marcus has "just**" connected the existing serial port to a small 3-pin jack out the side of the calculator to make it more convenient.

Nothing less and nothing more.

Quote:
BTW, as far as I recall, there actually is a USB-USB specification called On-The-Go (OTG) which will work peer-to-peer.

The TI graphing calculators make use of this specification. You can tell the difference by closely looking at the mini USB connector. The mini USB to mini USB cross over cable furnished by TI has a slightly different connector on one end.

Quote:
** When I say "just" here, I am still somewhat in awe of someone taking their Dremel tool and carving up the case to put this in! :-) Way to go Marcus!!

I vote for HP doing the modification. ;-)

The plug has the added benefit of missing the dangerous Erase and Reset buttons. With WP 34S once installed, Erase is no longer necessary because you can go to SAM-BA boot from within the firmware. Reset is possible with a paper clip.


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