Hello,
A certain incremental encoder has fallen into my lap.
Its a 2 channel hall effect (magnetic) unit - and the hall effect chips switch between .4 vdc and 1.2 vdc in its current circuit. For a full 360 degree rotation - it will switch 36 times between a full high-state and full low-state. But it is supposed to be useful for resolution down to the degree.
The hall effect outputs are analog producing sinusoidal rather than a square wave signal.
I suspect the design intention for this type of encoder is to perhaps drive it with a clock frequency instead of a constant + voltage. The clock frequency would be fast enough to split the the sinusoidal signals into slices.
So each sinusoidal cycle would look like a ladder incrementing up to 1.2vdc - and then decremeting back down to .4vdc
So if we sliced 1 sinusoidal cycle into 10 slices - and took a voltage reading during each slice (i.e. high clock state) then for a full 360 degrees of rotation - we would end up with 360 slices. Thus we get a 360 degree encoder.
I'm wondering if anyone has every worked with this type of encoder, and could you share how you did it?
got_arduino ------ looks like that encoder simply might not have the circuitry included that converts the rising and/or falling edges of the sinusoids to square-wave ------ or two level waveforms. Maybe it actually has ----- not sure (eg. got any more wires in the cable for it?).
Thanks all!
Yes - I think you're right - its a quadrature with two signals 90 degrees out of phase. And yes on the external circuit. It was part of a system that had a monitor. And I suspect the electronics within that monitor were chopping its signals up to get higher movement resolution out of it. Since it equates to 36 full sinusoidal cycles for one full revolution - that is why I suspected the electronics in the monitor must be slicing each one of those sinusoidal signals up into sequences and then interpreting direction and count accordingly - to get 10 times the resolution for each sinusoidal cycle.
However, I'm only guessing and without getting more detailed understanding I probably won't pursue using it with the arduino.
But my sincere thanks for your good thoughts on the matter!!
got_arduino:
Hello,
A certain incremental encoder has fallen into my lap.
Its a 2 channel hall effect (magnetic) unit - and the hall effect chips switch between .4 vdc and 1.2 vdc in its current circuit.
Most encoders are either open-collector (needs pull-up resistors), or differential signalling (A+/A-/B+/B-).
I suspect you lack the pullup resistors.
So I think what I have here is a sine/cosine encoder.
Something new to me
But from what I read - they've been around for a long time.
Used for example by HP in their old large printers.
Interpreting the output of this encoder is called "Interpolation".
And one way to do this is with constant A/D reads on the two sine/cosine signals - and performing trig math.
To save myself some time - I'm going to look for a possible off-the-shelf IC designed to do this.
With the hopes that I can read its output with the arduino.
Well - here is a wild idea that might possibly work to read this encoder.
First we amplify both encoder signals so we get 0vdc to 4vdc for each cycle - for both Channels.
Then we use 4 voltage comparitors to trigger high at 4 voltage points.
This gives us 5 voltage values for channel A, and 5 voltage values for channel B.
We then feed the comparitors into 4 Arduino pins e.g. PORTB - which reads these as a 4 bit word - having 5 possible decimal values.
And the other comparitors into 4 Arduino pins e.g. PORTD - which reads these as a 4 bit word - having 5 possible decimal values.
During movement - the first half of a sinusoidal cycle would resolve to the decimal values of: 0, 1, 3, 7, 15
During continued movement - the second half of the sinusoidal cycle would resolve to decimal values of 15, 7, 3, 1, 0
So in the CW direction - channel A values will shift from 15 to 7, while channel B values will shift from 3 to 7.
But in the CCW direction - Channel A values will shift from 15 to 7, while channel B values shift from 7 to 3
Thus we have one count for every shift in value, and direction can be ascertained by using a Switch-Case statement.
TomGeorge:
Hi,
Can you please post a picture of the units?
Does it have a name plate?
Tom..
TomGeorge:
Hi,
Can you please post a picture of the units?
Does it have a name plate?
If so what has it written on it?
Tom..
The company name on the PCB is "Tangent Instruments" and I understand they make encoder related products for Astronomy. And this encoder is for the azimuth axis of a telescope. But I haven't been able to get any more info beyond that. The left side shows the magnetic disk which is divided into 36 sections. The right hand pic shows the hall effect sensors and a filter cap.
