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I am using a Raspberry Pi 3, B+ pertinent libraries are WiringPi, with WiringSerial. Code is written in c.

EDIT: the Serial connection is handled through GPIO 14(Tx) & 15(Rx), 5v (Tx) is stepped down through 165 ohm resistor and, a 3.3v Zener Diode.

The following code is what I use to retrieve and and convert Raw Encoder Count to 16bit value.

int16_t sensors_left_encoder_init() {
int16_t left_encoder_start = 0;
char buffer_l[2];
int i = 0;

serialFlush(fd);
serialPutchar(fd, 142); // Request sensor packet
serialPutchar(fd, 43); // Left encoder request
do {
    buffer_l[i] = serialGetchar(fd);
    printf(" -> Left Serial Value: %d\n", buffer_l[i]);
    i++;
} while (serialDataAvail(fd));
left_encoder_start = (int16_t)(((buffer_l[0]) & 0xFF) << 8 | (buffer_l[1]) & 0xFF);
printf(" -> Left Encoder Start: %" PRId16 "\n", left_encoder_start);

return left_encoder_start;
}

int16_t sensors_right_encoder_init() {
int16_t right_encoder_start = 0;
unsigned char buffer_r[2];
int i = 0;

serialFlush(fd);
serialPutchar(fd, 142); // Request sensor packet
serialPutchar(fd, 44); // Left encoder request
do {
    buffer_r[i] = serialGetchar(fd);
    printf(" -> Right Serial Value: %d\n", buffer_r[i]);
    i++;
} while (serialDataAvail(fd));
right_encoder_start = (int16_t)(((buffer_r[0]) & 0xFF) << 8 | (buffer_r[1]) & 0xFF);
printf(" -> Right Encoder Start: %" PRId16 "\n", right_encoder_start);


return right_encoder_start;
}

I pulled the battery, ran the code and the first run produced:

-> Left Serial Value: 0 -> Left Serial Value: 1 -> Left Encoder Start: 1 -> Right Serial Value: 0 -> Right Serial Value: 2 -> Right Encoder Start: 2

However the second run through produced this:

-> Left Serial Value: 0 -> Left Serial Value: 3 -> Left Encoder Start: 3 -> Right Serial Value: 0 -> Right Serial Value: 4 -> Right Encoder Start: 4

I have a feeling its how serialGetchar() is receiving the serial output from the interface, but I am not 100%.

From reading the wheel encoder topics on here, and the OI Specs, I understand that the raw values should not change unless a drive command was issued to the interface.

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I'm not familiar with the Rpi3 UART capabilities as I'm using a different controller with a hardware UART, but I can report that others have had difficulties using software-based UARTS with later generation of Roombas, i.e. Series 500 and later

https://www.ez-robot.com/Community/Forum/Thread?threadId=10953

I suggest adding a USB-based UART dongle and see if that solves the issue

I think you are indicating that you are using a Roomba 690, which I thought was Wi-Fi only. If that's the case, how are you connecting to it?

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  • $\begingroup$ Thanks for the link! I was under the impression the PL011 which is the main UART on the PI was hardware, but I could be mistaken. I am using a Roomba 690, it does indeed have Wi-Fi, but it also has the same mini-DIN as the create 2. Only difference is that the create 2 is missing the vacuum components, and have an 7 Segment LED display (I think). $\endgroup$ – Pete Jun 19 '18 at 19:00
  • $\begingroup$ Where is the mini din located on the 690? Under the faceplate like 650? $\endgroup$ – Faengelm Jun 20 '18 at 19:26
  • $\begingroup$ It sure is; Located on the left front, under the outer face faceplate. $\endgroup$ – Pete Jun 22 '18 at 3:22

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