Differential Quad Encoder input circuit.

marzec309

OK, I need to read the A B and Z signals from a quadrature encoder. The outputs are Differential, a + and - for each channel. To spare some pins on the prop(My display is hogging a bunch already). I came up with a buffer circuit to convert the quad output to a single ended version(attached). It a very simple circuit and has an important feature,in that if both sides of the signal are not present it will not operate. Now my question is should i use a schimty trigger on the output of the buffer? Or is this sufficient for the prop to read. The signals from the encoder will be any where from 0Hz to 5KHz, possibly higher, but at the current speeds 5KHz is the norm. and will never exceed 20KHz. I'm using 2n3904 and 2N3906 transistor in the circuit and should be plenty fast enough for this application(I think). More or less I'm concerned about slowing down the level transitions.

GameHacker

In the past, I have used the 26LS32 I.C.·for interfacing to a differential encoder.· My application handled 5Mhz quadrature input with no problem.

Note: this was interfaced to this counter IC: http://www.usdigital.com/products/interfaces/ics/lfls7166/

Best of Luck!

-Brian

marzec309

Ya that sounds familiar as i was looking at a similar chip, But due to part availability in my area. I decided on a custom circuit, so i could use parts i have on hand. I wanted to keep it simple as not to introduce too much noise. So far what i have works pretty good on the bench. I'm just undicided on weather to use a schmity trigger before the prop to clean up any nasty edges. I guess I will have to pull out the scope and do a little more testing, to see how clean the signal is post buffer.

Phil Pilgrim (PhiPi)

To save components and space, you might consider using an RS422 receiver instead of the transistors. Here is a quad device that will handle all three channels.

-Phil

marzec309

Sound like a good idea. I'll have to dig my parts bin to see if i have a RS422 receiver.