View Full Version : DRO axis combining box.

10-25-2013, 11:36 AM
A while back I replaced the 2 axis Mitutoyo DRO on my BP clone with a three axis Sinpo system from The DRO Store. It ended up being a very good deal because I got 2/3rds of my money back selling the Mitutoyo on ebay and I've been quite happy with the new setup. I was going to add a standalone quill readout, but got thinking about combing the quill and knee axes. Several DROs have four inputs and can combine two inputs, but I wasn't finding many ready made external combing boxes. Newall do one for around $300 and I was thinking about making my own until I found a reference to one from Machine DRO (http://www.machine-dro.co.uk/digital-readout-systems.html). No details were available, but I got to talk to them at the Midlands Model Engineering show recently and they aim to make the box available in a month or so for around 65 ($105). I also got to speak to the buyer of my Mitutoyo DRO at the show and he's still happy!

10-25-2013, 04:07 PM
You could do it externally with a microcontroller. The simplest would be something like a Teensy or even better yet a Teensy 3.0. It has a lot of interrupts so you get fast encoder counting. A friend wrote a good encoder library, probably the best one out there right now:


do a little math and figure a way to output quadrature and you should be good to go.

10-25-2013, 04:40 PM
A friend wrote a good encoder library, probably the best one out there right now:

That type of decoding has been around for quite a while.

the interrupt on pinA - read pinb method is usually quite terrible.
the interrupt on pinA - interrupt on pinB is much better.

Silabs released some code in 2004 that uses the 2 interrupt method,but also switches the logic transition detection half way through an event.(to give a certain amount of filtration).

But in the real world where things vibrate (on transition edges) you still need a filter in a dedicated chips like the Agilent, LSI offerings or a dedicated QEI unit as per Microchip...
or a clpd.
If you go to the 8052.com site ...years ago Jez Smith (an Arm Holdings employee) uploaded a tested VHDL code snippet for a quadrature interface with excellent filtering..It works properly in the real world.


10-28-2013, 09:10 AM
If the box was going to be 100+ then I'd look at rolling my own. I've got plenty of stuff to get on with and 65 for a plug and play solution seems a reasonable deal.