Using the Serial Port on the HP 50g Graphing Calculator

[pin224466]

after having an opportunity to review the rs-232 cable solutions, just one additional note:

both designs appear to have a significant cable distance between the 3V digital output of the 50G and the "device" that converts that signal to rs-232 level.

This is a dangerous approach as the length of the cable can cause transmission line ring on the digital 0 to 3.3V side. Since the digital side is only 3V levels, that will help reduce the energy level of the ring. Regardless, the problem still exists and can cause errors in the transmision.

The "device" that converts the digital 3V to Rs-232 voltage levels should be located as close to the 50G connector as possible to help avoid this potential problem.... not at the end of a 6 foot cable...

[HP-MACH]

Hi!, zekelegge:

IMHO, you can see, for make serial connector, from ... http://www.educalc.net/2147084.page or ... http://www.educalc.net/2146080.page

[BartdB]

Hi Pin,

You have a valid concern about the distance of the 3.3v signal side ( I certainly wouldn't have it on critical designs). Ideally the interface device is inside the equipment, but unfortunately HP did not provide that. With the available connector-cable assemblies it is difficult to put the inteface device on the calculator connection side.

I have purchased a pre-assembled cable (I felt that for the price it was not worth the effort to make one up myself).

It is about 3 ft long and connecting the 50g to a PC, it operates without problems at 115 200 baud.

I have not tried connecting other devices to the 50g yet, but I will see what serial I/O devices I have and give it a try.

.

[pin224466]

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@Bart dB wrote:

( I certainly wouldn't have it on critical designs). Ideally the interface device is inside the equipment, but unfortunately HP did not provide that. With the available connector-cable assemblies it is difficult to put the inteface device on the calculator connection side.

.

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the level converters should be able to be kept very close to the 50G (for the OP's benefit see the attached drawing.. it is a modified version of drawing that Tiwag provided in the post).  A standard rs-232 cable can be used downline of the level conversion to extend the distance between the remote rs-232 device and the 50G.

Interesting that even for the Streamsmart 400, HP kept the 0-3v digital pseudo rs-232 cable connection short.

The problem is that we do not know what hp did inside of the streamsmart device to help terminate that logic level signal on a 1 foot cable.  HP may have significant passive filtering networks inside the streamsmart to terminate the 0-3v digital pseudo rs-232 signal and solve the problem.

We don't know what's inside streamsmart, that is, unless someone from HP can provide some insight on the streamsmart pseudo 232 interface design.

yes Bart, It will be good to know the results of any testing .

The problem we are discussing (when using a long cable length to xmit a digital signal) is not necessariliy a constant, repeating problem.  If the problem occurs it will be random and likely very intermittant.  In other words, it may only happen once every couple of days of constant rs-232 communication.

EDIT... having problems making the attachment stick to the post.  see later post for drawing...

[Ranothil]

 I am not sure how to tell that it will be compatible to the calculators RS-232 Port. It just says RS-232 Port in the System Requirments, so I thought that any serial port would work fine!

P.S. I keep trying to make the manual attach to my first post and it won't so I am not sure what is up with that myself 🙂

P.P.S. What is a level converter?

[pin224466]

O.K..   I give up trying to make an attachment to the last post.  For some reason the system is not allowing attachments at this time.

So here's the modified drawing:

[Ranothil]

Isn't that circut inside the Plug sold at Hpcalc.org?

[pin224466]

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@zekelegge wrote:

Isn't that circut inside the Plug sold at Hpcalc.org?

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This is the circuit diagram for Tiwag's post.

the two circuits are probably very close in design but not exact.  (especially since per the hpcalc web site text, the hpcalc cable/circuit board utilizes a microcontroller)

Bart likely has better understanding of hpcalc's circuit and can provide more informed comments.

Tiwag's circuit, while tapping the battery from the 50G to power the circuit board, also taps the rs-232 DTR and RTS lines to lower the power consumption from the 50G battery.

the hpcalc ciruit uses a max3221 to perform the digitial to rs-232 conversion.

Tiwag's circuit uses a st3232 (low voltage 232) to perform the digital to rs-232 conversion.

the primary difference between the 3221 and the 3232 is that the 3221 has a single input and single output and the 3232 has a two inputs and two outputs (tiwag shows one pair as unused).

The Vsupply specs on the 3232 part look slightly better than the 3221 (based on the datasheets I found).

with regard to the remainder of the hpcalc circuit, since there is no schematic available, maybe Bart can provide some insight.

[pin224466]

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@zekelegge wrote:

 I am not sure how to tell that it will be compatible to the calculators RS-232 Port. It just says RS-232 Port in the System Requirments, so I thought that any serial port would work fine!

P.P.S. What is a level converter?

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you'll have to contact the mfg to find out the specs.... OR connect the device up to your computer and change the computer 232 settings to see what works and what does not work.

it is a good guess that the 232 connection is either 9600,n,8,1  OR 4800,n,8,1  OR 2400,n,8,1

the 50G can communicate with any of those connection types.

see the Advanced User Reference commands:  BAUD, PARITY, OPENIO, CLOSEIO, SRECV, XMIT

the level converter discussed in prior posts refers to the electronic component that will translate the digital 0 to 3v signal generated by the 50G into a RS-232 compliant signal in terms of voltage level and impedence as seen by the RS-232 connected component.

[Dennis_Handly]

>I gave up trying to make an attachment to the last post.

What type of file was it, .jpg?  What browser were you using?