Logic levels on Myxa


(Max Abildgaard) #1

Hi Pavel,

we’re looking at using the Myxa controller for a small underwater drone that counts fish. We’re drafting the electronics board and I just need to clarify a few things for that process. I believe that most questions can be answered in a few words.

  1. Integration strategy: We’ll start out with a setup where we use RCPWM for control and UART to query for current, RPM, and temperature. Am I right in understanding that this is a working setup?

  2. The binary UART protocol can “found” in Kuscher’s source code – I understand. You don’t have some sort of example code for working the protocol between a Myxa and a u-controller?

  3. We are concerned about ground loops. Therefore the question, if power- and ground levels on the Myxa are connected? Do you recommend adding an opto coupler in the link between u-controller and Myxa?

  4. Logic levels: To what voltage level are UART and GIOs tolerant? What is their output level?

  5. Is AUX_VDD on the GPIO-port driven by the Myxa or by the host system/u-controller?


(Pavel Kirienko) #2
  1. Yes. You can also control the motor via UART.

  2. Not yet, sorry. Feel free to post questions here and we’ll provide examples.

  3. Yes. Yes.

  4. Output 3.3 V, input up to 5.5 V.

  5. This is the BEC power output in Myxa B, not connected in Myxa A.

(Max Abildgaard) #3

Cool. Perfect.

(Max Abildgaard) #4

Hi Pavel,

another (related) question: Could you specify the types of connector used on the Myxa. Especially the GPIO and the “serial” connectors.


(Pavel Kirienko) #5

The Aux and CAN connectors are JST GH (“UAVCAN Micro connector”, https://new.uavcan.org/specification/UAVCAN_Specification_v1.0.pdf).

The debug connector follows the Pixhawk Connector Standard, type JST SM06 (“DCD-Mini”, https://pixhawk.org/pixhawk-connector-standard/).

(Max Abildgaard) #6

Hi Pavel,

cool thanks.

/ Max

(Max Abildgaard) #7

1: RX/TX
Interfacing of UART RX and TX is something that I get wrong the first time - every time. So: On the debug connector, the figure reads:
Pin 2 is TX and
Pin 3 is RX.
Is that of the Myxa or of the “host system”?

2: Power for OptoCoupler
From earlier in the thread, I take that on the GPIO port, the AUX_VDD is not powered in my Myxa A. But I still need to power an opto coupler for the RCPWM. Is the assumption right that I can source power for this from pin 1 on the debug port (VDD_5V)?.


(Pavel Kirienko) #8
  1. Myxa. That is, TX is output.
  2. Your assumption is correct.