[Help] Read magnetic encoder

[shmulik]

Hello,
I have an absolute magnetic encoder (MB029+MBA029) that i want to buy (specific this model due to its small size and high resolution).
I want to read its position with a Teensy 3.2, and if its possible with no extra parts.
The encoder comes with 3 optional communication interfaces: (Datasheet P.17)

1. Asynchronous serial RS422(UART)
2. SSI
3. BiSS-C

As i understand only the "Asynchronous serial RS422(UART)" can be used with Tensy with no other parts like communication converots.
In the datasheet there is an explanation about this pins and how to request the encoder position.
But i still have truble with how to wire both of them:
The encoder has 8 pins: (Datasheet P.16)

• Vdd - 5V
• GND
• Temp sens 1 & 2
• RX +
• RX -
• TX data out +
• TX data out -

And there is an explanation which command do i send to get the info(pos/speed/temp/..) that i need (Datasheet P.18 bottom).

I dont understand where do i connect the RX+/- TX +/-
and which serial i send / read the indormation from the sensor.

Download the Datasheet


Best regards.

 

[Theremingenieur]

Looks like the RX and TX signals are symmetrical (thus the +/-), similar to RS485, which would imply the need for an extra transceiver IC to desymmetrize these signals.

 

[shmulik]

Can you please point me which part do i need ?

The second question is:
Does the SSI or BiSS need additinal parts too ?
I came across a thread where somebody wrote that he used SSI only with arduino. He wrote the clock protocol byhimself.
Do you think this could work ?
https://forum.arduino.cc/index.php?topic=92552.0
https://forum.arduino.cc/index.php?topic=156812.0

Thanks for the help !

 

[Theremingenieur]

I think that the RS422 protocol is the most robust and the easiest to implement, though. One IC, no clock worries, no additional coding, it can‘t be simpler. Just use the http://www.ti.com/lit/ds/symlink/sn65hvd379.pdf.

 

[shmulik]

Is there a board that this element is mounted to it ?
For example rs485 to UART: https://www.sparkfun.com/products/10124
or do they sold only by themselves: https://www.digikey.com/product-detail/en/texas-instruments/SN65HVD379DR/296-19628-1-ND/1016502

And is there any wiring schemes or code examples ?

Thank you again for the help.

 

[Theremingenieur]

Normally, for setting up a professional project, you would use the Sparkfun breakout for prototyping on breadboard until everything works well. Then, you’d design, test and (mass) produce your own circuit board where you solder the individual components and with a socket for the Teensy.

 

[shmulik]

I am building only a prototype.
Maybe i Missed something, is this board: https://www.sparkfun.com/products/10124
is suitable for RS422 too ?
it has different chip than you wrote before (sn65hvd379 - http://www.ti.com/lit/ds/symlink/sn65hvd379.pdf)

 

[Theremingenieur]

RS422 and RS485 are identical when it comes to set up 1:1 connections over short distances. The differences are that RS422 is exactly limited to that while RS485 allows up to 32 transmitters on one line and that RS485 allows link distances > 1km depending on the baud rate.

Thus, that spark fun board should normally do the job. It's worth trying it. I suggested the SN65HVD379 because it's one transceiver chip which I know and which is suitable for 3.3V operation with the Teensy. But as always, many routes lead to Rome.

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