Powering Adafruit M4 CAN

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JanZ1961
 
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Powering Adafruit M4 CAN

Post by JanZ1961 »

Hi there,

I'm new to this forum and new to the Feather. I have some experience with Arduino's en ESP32. Until recently I used a Longan board for CAN bus, but I had problems with those freezing and recently I couldn't get them back to life. Enter the Feather.

I really love them. Okay, it is all 3.3V instead of 5, but I can live with that. What does present a problem is that it doesn't have the 7 - 20 V input. Because in automotive application, 12V is easy to find. And the sensor that I want to use requires a voltage between 10 and 30. So what is the plan.

I want to do some datalogging on a motorbike. My datalogger can sample analog input at 500hz and for the suspension, I wanted more. I can easily get 1000Hz and may datalogger can handle 1MHz CAN. Also, moving to CAN reduces the number of cables.

So I have a Feather M4 CAN the samples a number of temperatures (from the tires), the suspension position and the wheel speed. This data is put in CAN messages. The cable from the datalogger has four wires: CAN hi, CAN lo, 12v and GND. Since I can't power the Feather with 12V (like I could with the Longan board), I use a buck converter to get 5V. But (and I finally get to the point of this post) if I connect a USB cable to see what the Feather is logging, I am taking a risk according to what I'm reading in the "Power Management" section.

How big is that risk? Would the buck converter brak from the USB power, or te USB host (my computer) from the power coming from the buck converter? Does anyone have an idea to make this safe (apart from a pysical switch).

I'm curious to your ideas on this so, thanks for any response.

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dastels
 
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Re: Powering Adafruit M4 CAN

Post by dastels »

Big risk (probably certain). While you can use a diode to protect the buck, there's no protection of the 5v line of the USB. One approach would be to use a hacked cable (or adaptor that disconnects the 5v USB line or uses a diode on the 5v line (cathode toward the feather). That still relies on you using it when appropriate (when the feather is powered by the external power source. If it could be placed inside the enclosure that would help make it hard to forget.

Dave

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JanZ1961
 
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Re: Powering Adafruit M4 CAN

Post by JanZ1961 »

That was exactly my idea. Thanks for confirming it. And it will be inside the enclosure anyway because the feather will be inside a waterproof casing (remember: motorbike :-)). I think I will use two diodes to protect both.

Now on to selecting a diode. Anyone that can handle 500mA will probably suffice.

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dastels
 
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Re: Powering Adafruit M4 CAN

Post by dastels »

I'd use a 1N4001 or 1N4007. Classic power diodes. Very common, quite cheap. Out of stock at Adafruit at the moment but Digikey or Mouser have them.

Dave

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JanZ1961
 
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Re: Powering Adafruit M4 CAN

Post by JanZ1961 »

Exactly the one I picked (luckily I had my own stock). Thanks, albeit delayed, for your help.

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