[chbot] TTL to Line driver

Mark Atherton markaren1 at xtra.co.nz
Sat Sep 12 22:20:18 BST 2020

Hi Wallace,

Have you looked into why your existing encoder is intermittent ? I have 
seen problems with damaged seals leading to moisture and dust ingress, 
which have in turn clogged the optical wheel. Also failed buffer ICs can 
cause issues. Careful optical cleaning, and driver replacement is quite 

Assuming that this is not possible...

Your description of single ended to differential TTL conversion sounds 
suspiciously like a conversion between TTL and RS422. There are lots of 
ICs available to do this conversion including the 26C31, which is a quad 
RS422 driver IC. https://www.ti.com/lit/ds/symlink/am26c31.pdf

For optical-encoder type applications a popular signalling format is a 
pair of quadrature signals (A+B) along with an index pulse (X). A have 
some industrial shaft encoders which require power, and generate 3 pairs 
of RS422 compatible outputs carrying A, B and X.

So how many channels do you need ?

 From you original posting, it is unclear if you are looking for a 
driver IC, an assembled PCB, or a complete, enclosed product.

RS485 is a half-duplex implementation of RS422, so it is possible to 
take an RS485 unit, and wire it permanently in transmit. Hence my 
original suggestion that https://www.trademe.co.nz/2775249657 might be 
of use, but you may need several of them.

Hope you are well,


PS The SN75183 you reference is a dual RS422-like driver, with a rather 
odd-ball input arrangement.


My encoder has become intermittent on my CNC mill. I have found that my 
Liner  scale from Aliexpress has the correct resolution to work with the 

The problem I have is the linear scale is TTL output and the connection 
I require is differential equivalent to a SN75183.


Anyone know of an off the shelf TTL to differential unit. My searches 
don't yield much other than discrete components.  Maybe there is another
  workaround ?

Thanks Wallace.

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