Hi
I have used this project as an excuse to learn KiCad.
I have gathered together the good ideas of others to create the bestest and most marvelous version of the schematic and PCB for the USB-GPIB adapter.
"My" design is a combination of the best features I see in other designs, plus a couple of features I have dreamed up.
The fruits of my effforts can be found here:
https://github.com/dazz100/UsbGpib/tree/USB-GPIB-Dazz/HW/DazzThe changes made include:
- Adding ESD protection,
- Adding USB-C connector,
- Used hand solder friendly larger 0603 sized components,
- Added 2x options for mounting bi-colour LEDs,
- Added 2x 3mm mounting holes to anchor the enclosure to the PCB.
- Used a rectilinear shaped PCB to make it easier to use on stiff connectors.
The USB-B connector is chunky and robust but relatively large.
The USB-micro may be too fragile for knocking around in the lab.
The USB-C seems to be the Goldilocks choice.
The larger 0603 sized components will make it easier for the visually challenged to hand solder this project.
I think the addition of a second LED can be used to convey useful status info to a user, much like the LEDs on an ethernet socket.
I have added a LED to a spare output of the MCU. The original software will continue to drive one LED. The software will need to be modified to enable driving the second LED.
I have found that there is no standard orientation of the rear panel connection. Readily available bi-colour SMD LEDs point upwards. I have added the option of fitting right angle LEDs on the end of the PCB (opposite the USB). Regardless of orientation, these should always be accessible to see.
Centronics connectors can be stiff to insert/remove. The addition of two mounting holes will allow the enclosure to be anchored to the adapter with 3mm screws.
For similar reasons, I have used a rectilinear PCB to make it easier to include finger grips in the design of the enclosure. The PCB has been slightly extended so there is some bare PCB that can fit into a slot within the enclosure to further anchor the enclosure to the PCB.
The form factor of a "standard" GPIB cable assembly is side entry. This is similar to the form factor of my PCB/enclosure design. I see no advantage in a stepped shape of the PCB.
I decided very early not to make any hardware changes (eg. pin allocations) that would require code changes. This includes the bi-colour LEDs which will run as a single LED mode on the current software version. So although this version is only similar in hardware design, it is not essential to modify the software.
I haven't yet decided whether the enclosure will be a one-piece "cup" or a two-piece clam shell.
I think this is a really good project and the incremental development by others has only improved the outcome. I have three items of old test equipment with a GPIB bus so this adapter will be a way of increasing their usefulness.
I am seeking feedback on the schematic and pcb designs. Have I got it right?? Is there a feature missing?? Any feedback would be welcomed.