DS 26C32 ATM line driver and PCB-Design for measuring microscope

[Thomi3D]

Thank you very much for this great project, @MrGreensWorkshop.

My goal is to retrofit an old digital measuring microscope that has three RS422 glass scales with this DRO and the Raspberry Pi HQ camera. For this purpose, I want to change the DS8923 line driver to the DS 26C32 ATM, because of its availability in Germany. I would also like to design a PCB so that everything is nice and clean. Later on, my goal is to connect the Pico to a Raspberry Pi 4 that handles the camera.

Can you help me with this?

[MrGreensWorkshop]

Hi, I'm glad to hear that. Thanks for reaching out.
I think I mentioned in the video that the DS8923 is a 5V device, but when I use a 5V supply, it gets too hot. I connected to a 3.3V rail to reduce current consumption and heat. Since I connected to a 3.3V rail, I didn't need to use a voltage level shifter between DS8923 and RpiPico.

DS26C32AT is also a 5V device. It should be connected to 5V.
The datasheet says the minimum supply voltage is 4.5V, which means they tested until 4.5V. But that doesn't mean it cannot work below 4.5V.

You have two choices:

1. You can test with a 3.3V supply, and if it works, you can go with it without using a level shifter. (not recommended. Maybe only for test purposes.)
2. Or you can connect to a 5V supply and use a voltage level shifter between DS26C32AT and RpiPico.

The voltage level shifter doesn't need to be bidirectional. You may also use a fast-switching MOSFET or transistor for voltage level shifting. Since there are three axes, you may want to use a level shifter IC to reduce components.
I will check both datasheets and get back to you.

[Thomi3D]

Hello @MrGreensWorkshop,

thanks again for your effort.
I will try to design a circuit when i find the time and get back to you.

Greetings
Thomas

[Thomi3D]

Hello @MrGreensWorkshop,

this is what i came up with:

I hope it's not completely wrong, and I'm looking forward to your feedback. :)

Greetings
Thomas

[MrGreensWorkshop]

It looks good to me. 
Pin 26 is used for A input, and pin 27 is used for B input. It is reversed, but not a big deal. 
One more thing. I don't know how many drivers you are going to use, but please don't forget to check the Raspberry Pi Pico's 3.3V regulator datasheet to make sure it can supply enough power.

[Thomi3D]

Thank you for your feedback. The Picos 3.3V has a maximum output of 300mA, which should be sufficient for the three drivers I'm planning to use. I will order the parts now and will keep you updated on the progress. :)

Best regards,
Thomas

[MrGreensWorkshop]

No problem at all. Thank you for bringing up AM26LV32CD.
Good luck!