[Paparazzi-devel] Umarim hardware question

[Karoly Molnar]

Dear All,

I have a number of questions to the Umarim hardware design. I really appreciate the effort that someone has put in designing and testing this circuit so please do not interpret my questions offensive. There might be a certain motivation behind the design decisions that I do not see yet.

1. The pressure sensor is powered from a voltage reference. The guaranteed output current of this reference is 5mA while the average current consumption of the pressure sensor is 6mA. I guess the designer wanted to keep the voltage as precise as possible in order to have a stable output value but the reference circuit is apparently operating beyond its normal working conditions so this goal is hardly achieved.

2. Also for the pressure sensor, I see here a 16bit ADC connected to it that is powered from 5V and then connected an I2C level translator. Couldn't have been simpler to power the ADC from 3.3 V and match the voltages on the ADC input?

3. Also there are I2C pressure sensors available, why wasn't that used?

I am just guessing that the complicated design has the aim to provide an extremely precious pressure reference. I am still beginner in autopilots so it could be the case that such accuracy is really needed, but at first glance it seems just too complicated to use 5 integrated circuits to get a pressure value.

What do you think?

Regards

Karoly Molnar