USB-Datapak-CommsLink

This special section for all the COMMS LINK and communications issues
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MartinP
Posts: 52
Joined: Wed Jan 04, 2023 7:51 pm

USB-Datapak-CommsLink

Post by MartinP »

I made a couple of small developments to my USB Comms Link, which was posted on the old forum, I added a potential divider as a level shifter on the output, the 74HC125 buffers are 3.3V to 5V compliant, so they provide the level shift to 5V for the Psion's Rx serial input. I noticed some others are having a go at building their own, so I thought I'd re-post about it. I used a datapak to store the CommsLink ROM, to avoid the added complexity of re-creating the datapak addressing circuit in the Comms Link, this allows to make a Comms Link with only two ICs. I also used a UART to USB adapter (of the type built into the USB plug shown here, a CP2102) to avoid an RS232 level shifter plus adapter to USB. The CP2102 is a 3.3V chip, but is also 5V compliant on the input, so the potential divider isn't actually necessary with this one. I used this board with my MP3 player, which is 3.3V. viewtopic.php?t=25
Some might think this avoiding of the full circuit is cheating, but I like to keep things simple. I also previously built a Comms Link using only a handfull of BJT transistors which I'll post again in another thread.
Martin P.
USB-Datapak-CommsLink_w.jpg
USB-Datapak-CommsLink-sch.PNG
USB-Datapak-CommsLink-PCBv2.PNG
EDIT: I noticed a wire in the wrong place in the schematic and corrected it, please let me know if you find any others.
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amenjet
Posts: 237
Joined: Tue Jan 03, 2023 7:54 pm

Re: USB-Datapak-CommsLink

Post by amenjet »

Martin,

An interesting approach to a comms link. For anyone else doing this, i think I'm correct in saying that the datapak has to be a linearly addressed one? Not paged or segmented?

Andrew
MartinP
Posts: 52
Joined: Wed Jan 04, 2023 7:51 pm

Re: USB-Datapak-CommsLink

Post by MartinP »

Andrew,
Yes, if a datapak is plugged into this board at the top slot, then it needs to be a linear one. Many datapaks of size 32k or similar can be modified from paged to linear by altering a solder jumper on the board, see picture below.

But my Comms Link board will also work with a datapak plugged into one of the usual Organiser datapak slots, and then any type of datapak with the Comms Link ROM OPK image can be used. Using the datapak in a standard slot would allow a simpler board at the top slot, without the datapak connector, but has the disadvantage that a slot is used up.

I've been swapping my Comms Link datapak between top position or slot, depending on whether I want a more compact system, or if I want to use the other slots. Note that the Comms Link software has to be uninstalled when making this swap (by pressing On-Clear at the main menu, with the pack removed) and then re-installed (with another press of On-Clear at the main menu, when the pack is in its new location).

Martin P.
Paged & Linear Datapaks_labelled.png
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Martin
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USB-Datapak-CommsLink

Post by Martin »

Fascinating Martin

Am I correct that if you use Comms22.opk you get a 2 line version Comm Link and with Comms42.opk you have a four line version?

Also I tested one of Andrews Top Slot Adaptors with 'bare pins' and I cross connected it (I think 1 pin to the right) and fried the board - luckily not the Organiser. So I know about taking care when making the connection..

Is it taking its power from the Organiser battery?

Sincerely fascinating
Martin
MartinP
Posts: 52
Joined: Wed Jan 04, 2023 7:51 pm

Re: USB-Datapak-CommsLink

Post by MartinP »

Martin,
I used comms42.opk which works with both 2-line and 4-line organisers, it detects which one and runs accordingly. The earlier 2-line version should also work with this board, but I haven't tried it yet.

Not having plastic around the connector to ensure it's inserted correctly is a potential risk, and because VB is on one of the pins, it could cause some damage if connected to the wrong place. Using 4000 series logic chips might be safer, as these will take higher voltages. I've been thinking about adding some simple plastic tabs around the connector to ensure correct connection, I'll post something later when I've tried it out.

This board takes power from the Organiser, but as there are only two CMOS chips, the load is quite small and it's only powered when the slots are enabled. The USB adapter takes its power from the USB port, so there's no load on the organiser from that, and with some mods this USB 5V could be used to power the board.

A major thing missing is an external supply connection to enable powering of the organiser, but that could be added later. I designed this board so that other boards could be placed as a second layer on top (like my mp3 player) and a boost circuit or power connector could be added there.

Not fitting in the original Comms Link case is also a down side, but Andrew's board does that. This board is more of something to experiment with, or to provide a cheaper option. I did plan to fit it in a plastic case and that's how I decided on the board size.
Martin P.
amenjet
Posts: 237
Joined: Tue Jan 03, 2023 7:54 pm

Re: USB-Datapak-CommsLink

Post by amenjet »

MartinP wrote: Fri May 12, 2023 7:58 pm Martin,
I used comms42.opk which works with both 2-line and 4-line organisers, it detects which one and runs accordingly. The earlier 2-line version should also work with this board, but I haven't tried it yet.
I have modified comms links by replaing the ROm with the V4.2 and it works well on 2 and 4 line Organisers.
Not fitting in the original Comms Link case is also a down side, but Andrew's board does that. This board is more of something to experiment with, or to provide a cheaper option. I did plan to fit it in a plastic case and that's how I decided on the board size.
Martin P.
I think the USB adapter I designed is probably about the same cost, maybe a little more, maybe a little less. One very big difference between this project and my adapter is ease of construction. It's not practical to build my board without reflow equipment. This project is far far easier to make and experiment on. Experimenting on my PCB would not really be possible.

Andrew
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