Allegro ACS758

[frater]

Sorry for being slightly OT.
I'm placing it here because it gives me the best chance of getting a good reply.

I have implemented an Allegro current sensor on the analog input of my SP Racing F3 flight controller.

Because it has a max 3.3V input I decided to supply the Allegro sensor with a 3.3V as well.

According to specs the 100 Amps unidirectional has 40 mV/A and the 50A version 60 mV/A. I'm using a 50A version on my racing quad.

I thought I could just tell cleanflight to use 40 mV/A, but it seems I need to give it a much lower number.

Is it because I'm using it on 3.3V instead of 5?

I have a 200 nF on the output of the Allegro sensor, but the FC is not giving out a constant value. Should I add a resistor, use a bigger capacitor or can't this behavior be avoided?

[Carbo]

Did you see the cli documentation? There are descriptions for current_meter_scale and current_meter_offset.

The ACS758 datasheet has informations about "Output Load Capacitance" (max. 10 nF) and "Output Load Resistance" (min. 4,7 kOhm). I think you can keep the 200 nF, but with a 10 kOhm R between VIOUT and the cap. If the value is still jumping, increase the resistor, if it reacts too slow, decrease the cap. There is also a "Typical Application" shown in the datasheet.

The ACS758 will work with 3.3 V.

[jhsa]

Just a note..
The offset is calculated at 0.12 * VCC.
So for 5V the offset (voltage at 0 Amperes) is 0.12 * 5 = 0.6V
For 3.3V the offset is 0.12 * 3.3V = 0.396V

João

[frater]

Thanks both....
I will try a resistor after I get back from holiday