Ardecoder: decoding up to 3 encoder with Arduino Uno or Nano.

INSTALLATION

It is assumed everything needed to build a project for your board (most notably arduino, arduino-cli and board support) is already properly installed on your system.

Ensure the Arduino board is connected to the PC and then:

# For new Arduino NANO:
make upload
# For old Arduino NANO (prior than 2018):
make MODEL=nano:cpu=atmega328old upload
# For Arduino UNO:
make MODEL=uno upload

By default, the makefile expects the board to be connected to the /dev/ttyUSB0 device. If this is not the case, you can explicitly specify another device, e.g. make DEVICE=/dev/ttyS1 MODEL=uno upload.

ELECTRICAL CONNECTIONS

D2	Encoder 1 (A)
D3	Encoder 1 (B)
D4	Encoder 2 (A)
D5	Encoder 2 (B)
D6	Encoder 3 (A)
D7	Encoder 3 (B)
D9	Encoder 1 (Z)
D10	Encoder 2 (Z)
D11	Encoder 3 (Z)

If fewer encoders are needed, do not connect them. This also works with incremental encoders without the Z index: in this case the counter will be set to 0 at startup and never reset.

You can skip any encoder, e.g. you are allowed to connect only encoder 2 and 3 without using encoder 1.

To improve reliability, you can put photocouplers between encoder and arduino, as shown by the above example where only encoder 1 is connected (see the schematic for details). In that case, remember to consider the maximum speed of the photocoupler too.

A public video shows another example on Arduino UNO without photocouplers.

HOW DECODING WORKS

The code keeps the last state of A B phase (old) and compares it to the new state (now). Any variation will increase or decrease the counter (raw) depending on a lookup table (lut).

If OVERFLOW is defined, it is checked if a phase is skipped (e.g. when the encoder is turning too quickly) by leveraging another lookup table (skp). If that is the case, the counter is incremented or decremented by 2, depending on the last adjustment.

                 _______         _______
        A ______|       |_______|       |______
CCW <--      _______         _______         __  --> CW
        B __|       |_______|       |_______|

now A B	old A B	lut	skp
0 0	0 0	0	false	No movement
0 0	0 1	+1	false
0 0	1 0	-1	false
0 0	1 1	0	true	One step has been skipped
0 1	0 0	-1	false
0 1	0 1	0	false	No movement
0 1	1 0	0	true	One step has been skipped
0 1	1 1	+1	false
1 0	0 0	+1	false
1 0	0 1	-2	true	One step has been skipped
1 0	1 0	0	false	No movement
1 0	1 1	-1	false
1 1	0 0	+2	true	One step has been skipped
1 1	0 1	-1	false
1 1	1 0	+1	false
1 1	1 1	0	false	No movement

All 3 counters are adjusted according to the above decoding algorithm by the PCINT2 interrupt handler, called whenever any of the PIND bits (i.e. any D0..D7 digital input) changes.

PERFORMANCES

No serious attempts at counting CPU cycles has been performed. I am not even sure how much the serial communication impacts the overall performance but I am pretty confident this thing can read more than 20K steps per second with 3 encoders enabled and OVERFLOW disabled.

On real test cases I have seen counting more than 30K steps per seconds (more than 3K steps in 0.1 seconds, to be exact) but I think I am just hitting the speed limit of the photocouplers I used.

PROTOCOL

The communication protocol on the USB bus is text based, so it can be used interactively with a serial console. Requests and responses are expected to be newline terminated, and any newline format is accepted: "\n", "\r" or "\r\n". Anything between "#" and a newline is considered a comment and it is ignored.

GET ENCODER DATA

To query an encoder, just send its number (1, 2 or 3) followed by a newline.

• Example request: "1\n"
• Example response: "1 -581 0 1\r\n"

The returned fields are respectively:

1. the number of the encoder (1, 2 or 3, the same as the request);
2. the raw counter value;
3. 1 if homed (it passed through the Z phase), 0 otherwise;
4. the number of times a phase was skipped (if OVERFLOW is enabled).

SLAVE OR PUSH MODE

In slave mode (the default), you must manually get the encoder data via specific queries. For monitoring you must implement by yourself a polling loop.

In push mode, additionally the encoder data is sent without request whenever its position changes. The maximum rate of changes (i.e. the minimum time between two unsolicited responses) is customizable

To enable push mode, use "S" followed by the rate time (in milliseconds) and a newline. To disable push mode and turn back in slave mode, specify a rate time of 0.

• Request to enable push mode every 0,2 s: "S200\n"
• Request to disable push mode: "S0\n"

LICENSE

Ardecoder is MIT licensed.