@Rongzhong Li This schematic is exactly the one I've been looking for! It clearly shows a pull-up resistor on the Reset line and also explains why I couldn't get it working at first (using the RST pin 7). Now it is clear and I've been able to make a modification to the autoreset code. It will after a short delay change the pin into high impedance mode, which allows the pull-up resistor to pull Reset back to VCC. DTR will float around, but it looks like it is fine if it just goes to GND at the proper moment (as instructed automatically by Arduino IDE). The modifications (in bold) to /usr/bin/autoreset are the following: pin = 7 GPIO.setup(pin, GPIO.OUT) GPIO.output(pin, GPIO.HIGH) time.sleep(0.12) GPIO.output(pin, GPIO.LOW) time.sleep(0.1) GPIO.setup(pin, GPIO.IN) Please test it yourself and I'll update the original instructions accordingly!

Certainly! Please do so.

The RST and DTR pins are different on the Arduino Pro Mini. RST is used for resetting it and DTR is used just to initiate the programming. Therefore you cannot use the same pin for both. As an enhancement proposal (maybe for NyBoardV1?) you could consider changing the 2x5 socket into 2x6 socket. This way Pin 11 (in fact GPIO 17, corrected now in the instructions) can be used for DTR (as in my configuration) and Pin 12 (GPIO 18) is left to be used for something else.

@Rongzhong Li I got the programming working directly from RPi using the GPIO pins. The only addition is another GPIO pin to be used for connecting Pi to DTR. Apart from that a few settings are needed for Arduino IDE setups (namely for avrdude). I'll make another post as soon as I verify the steps with a vanilla RPi Zero W, which is a lot nicer from current consumption perspective than RPi 3B+, which I used as the initial test vehicle. I would also like to completely get rid of the Desktop environment and use RPi in headless mode. For this I still need to figure out how to compile INO files into HEX files without invoking Arduino IDE. Transferring HEX to Arduino is straightforward from the command line, but I didn't find a way to do the compilation into HEX without the IDE. If someone has the knowledge already then feel free to save me some time on this one!

I'm planning on trying to program Nybble directly with Raspberry Pi without the FTDI. The problem with FTDI is that the socket location is not really accessible when Raspberry Pi is mounted. Arduino IDE can be configured to allow serial programming using the GPIO pins. However, what seems to be missing in Nybble-RPi connection (2x5 socket) is the connection to DTR. First I thought it was the RST pin, but that seems to be the the master reset for Nybble. Before banging my head too much to the wall is there a ready made solution to this already? My thought for moving forward was to grab DTR from the FTDI connector and connect it via a wire to an arbitrary GPIO on the RPi. This GPIO can then be configured to be used for DTR by Arduino IDE. Maybe the question is whether the Nybble-RPi 2x5 socket connections RXD and TXD can be used similarly to TXO and RXI in FTDI port in order to program ATmega on Nybble? I didn't find the schematic for NybbleV0 and it is quite difficult to figure out the connections from the PCB layout pictures.

@Rongzhong Li I got Nybble under control again, thanks! If it helps others here's what I did: 1) Fully recharged the batteries 2) Uploaded writeInstinct and Nybble again (in this order), but it didn't help yet 3) Uploaded just writeInstinct and re-wrote instincts, then uploaded Nybble, but still the same problem 4) I then figured that it might be an issue of the servos being in wrong starting place (as the limbs had gone nuts) so I unscrewed all the limbs and powered Nybble up, which resulted in the servos turning a lot. After this I re-connected the limbs, checked the calibration (had to do a few minor tweaks) and voilà everything was back to normal. Next I'll actually measure the servo voltage and tune it accordingly in order to save power. Thanks!

First of all congratulations on this excellent work Rongzhong! I've assembled my Nybble and calibrated it successfully. It reacts to all to commands pretty well, but sometimes the servos (and thus limbs) just go nuts. The only way to recover is to quickly shut Nybble down. After the last of such events it didn't react to anything anymore so I uploaded Nybble.ino again. Now I have a problem that all I get in the serial monitor is: * Starting * Initializing I2C Connecting MPU6050... Testing connections... MPU successful Initializing DMP... 842 -48 38 2 Enabling DMP... Enabling interrupt detection DMP ready! * Assigning 1 skill addresses... 0 0 0 0 0 0 0 0 0 Finished! FIFO overflow! Using last reading! 7 7 k FIFO overflow! Using last reading! FIFO overflow! Using last reading! CH CH d shut down servos FIFO overflow! Using last reading! CH CH d shut down servos FIFO overflow! Using last reading! 7 7 k FIFO overflow! Using last reading! FIFO overflow! Using last reading! Nybble doesn't seem to recover from this. Any thoughts or ideas?