HP-97S I/O testing

[Hiwi]

Hi all,
i have a HP97S on my desk for repair. A friend acquired the calc recently on ebay.
Typical text from the seller: No magnetic card on hand so i could not test the reader, printer transport with minor problem and easy to fix with links to this forum, haha.

I never had a 97S, so i was exited to test the I/O function first. I fixed the battery. There were no test programs on magnetic cards nor the original testplug provided.

So I made a test interface with an Arduino micro. I took 4 data lines and multiplexed them to
4 x 8 Bit latches 74HCT373, CLK triggered from 4 other lines.

It took some time to figure out to activate the interface and adopt the logic (positve/negative)

Amazing how flexible this box is.

The interface can be triggered to accept data by one line, can send a kind of ACK and set 3(4) lines with simple SF/CF function to switch e.g. relay or leds.

The flag 3 enables the input from the interface directly to the display / keyboard buffer.
Sending a byte 'C' calls subroutine at label 'A'. So you have a simple program control.

The data input uses a simple serial line via usb.

A very nice machine. :-)

           

[TellyS]

Hi Hiwi,

It is indeed a remarkable calculator, probably one of my top favorite HPs. I purchased one on eBay a long time ago, but it was not working. I decided to replace all ICs on the interface in hopes that the problem was there. There is only one HP-proprietary ROM chip for which a replacement probably does not exist. Luckily that chip was fine. It worked! I have attached a picture of the board with the replaced ICs in case someone wants to do the same.

I ran several programs on it, but my favorite is something I built using a BASIC STAMP processor and a voice module. Commands could be given to the 97S via voice.
Video is located here: https://spyropoulos.net/files/TalkingCalculator.mp4
(Apologies for the low resolution video. It's several years old. I will have to redo with Arduino.)

Telly

[Hiwi]

Hi Telly,
an amazing project! So there is much fun and room for new experiments in the next years.
Do you know for what target group it was developed and how many were produced?
I never had a 97S before.
Ralf

[TellyS]

Ralf,

I know that the intention was to connect to simple devices, such as a scale that would weigh an envelope and the HP program would calculate the postage. There were probably similar devices that it was used for.

I have connected it to a few more things, like a Mitutoyo caliper (just because I had one). The caliper has an interface that reports the measurement with the press of a button. It was used for quality control. The caliper would measure and print certain measurements of a manufactured part to a Mitutoyo printer, but it was fairly easy to interface it with the 97S to do the same.

The attached PDF shows the pin assignment and signal format. I had to create a special cable for it.

Telly

[Hiwi]

Hi Telly,
which Mitutoyo do you use? Does it BCD output?
And what about signal levels? Even the Mitutoy0 has 1.5V levels i suppose.

I took a simple caliper with standard 24Bit data protocol.

So I had to add some protocol changer and level shifting electronics :-)

   

Ralf

[TellyS]

(09-30-2024 11:06 AM)Hiwi Wrote:  Hi Telly,
which Mitutoyo do you use? Does it BCD output?
Ralf

Ralf,

I just moved, so I need a couple of days to get back online properly. I will respond as soon as I can. But I have two Mitutoyo calipers.

Telly

[TellyS]

(09-30-2024 11:06 AM)Hiwi Wrote:  Hi Telly,
which Mitutoyo do you use?
Ralf

Ralf,
I finally located the Mitutoyo after my move. The first one is a Solar one. The second one uses a special round connector that I was able to locate and create a cable for it.

Telly