Does the SimpleFOCShield v3.x actually support 3.3v MCUs?

hardware support
1

Hi all,

I’m trying to connect my SimpleFOCShield v3.1 to a Sparkfun Thing Plus ESP32-S3, which is a 3.3V board.

I noticed that the SimpleFOCShield does not have an internal 3.3V regular, rather it outputs 8V on the Vin pin. So I will regulate that down to 3.3V for the ESP32 with an external regulator, no worries.

For the current sense supply, the SimpleFOCShield expects either a 5V or 3.3V regulated input, selectable by the user with a jumper at the bottom of the board. However, looking at the datasheet of the ACS712 current sensor chip it looks like that doesn’t actually support a 3.3V supply… The allowable input voltage range is from 4.5 to 5.5 volts.

Am I missing something? Has anybody gotten current sensing to work with a 3.3V supply?

2

Hi @Jeremiah_Rose ,

You are abosolutely right!
The ACS712 does not support 3.3V, at least in their datasheets.

However, in my tests I was able to run them consistently at 3.3V without any issues. :smiley:

Also if you use them at 5V rather than on 3.3V. The gain is 0.185 V/Amp and the range of 5Amps would give you the voltage range:

[ 2.5 - 5\times0.185,\quad 2.5 + 5\times0.185 ] = [ 1.575,\quad 3.425]

So it would be just shy outside the range of the 3.3V adc input. The max current you could measure with a 3.3V adc would be

(3.3-2.5)/0.185 = 4.32Amps

Hope it helps!

3

Great, thanks Antun!

4

Haven’t tested current sense yet, but it looks like the AMT103 encoder also works fine at 3.3v (despite its datasheet specifying 5V).