differential linear glass scale output

Projects General Guidance
1

Hello hopefully someone smart will be able to point me in the right direction. Im looking read a linear glass scale with my arduino for a project im doing. Only problem is i have some glass scales that are single ended and some that are differential (eia422)

I would like to build a standard circuit that would allow me to connect either of these types to my arduino and read the quadrature signal of them. I guessed that i need a differential receiver like sn75175d but then if i put my signal through this im not sure if my single ended scales will work.

Ive been looking on the internet and saw that this person has managed it but looking at the pcb traces and the chip he has used it seems to be wired in a very strange way. The is he is using is a AM26LV321 which is a DIFFERENTIAL LINE DRIVER and from what i can see its wired like this (ive only drawn in one signal pair)

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This is the website where i saw this method.

Can anyone explain how it works and even if my understanding of how he has managed it is correct?

Many Thanks

Trev

2

Unusual. Y and Z are the outputs of that chip. So why is Y connected as an input? If it's connected to a differential input then I would have expected the inverted output (Z) to be connected as a kind of "follower" on that input.

You can convert any differential input to single-ended by either grounding or ignoring the second line. Ignoring it only works if there's a separate ground connection. I think that's what's going on here.

3

Every connection deserves proper termination. RS-232 transmits a voltage, RS-422 or RS-485 a current. You need appropriate line drivers and receivers for each type, and a multiplexer for connecting the right receiver to the Arduino RX input.

Eventually both inputs can be mixed together by use of diodes or logic gates, provided that the receivers output the same logic level with no sender attached. Otherwise a mechanical or digital switch is required, that connects the RX input to the receiver to use.

The TX pin instead can be connected to both senders, no switch required.

And of course only one station (scale...) can be connected at the same time to Serial. You have to disconnect all circuitry when programming the board, because the USB port uses Serial as well.

4

Thanks guys, i got the scale linked up by a diff line receiver ic and all is good.

I was just intrigued how he managed to do it with that ic.

thanks again

Trev