RAK3172 + RUI3 + ADC Part-2

[dinesh (Dinesh Ananda Lohar)]

Hi,

This is in continuation to my last query on ADC as below

RAK3172 + RUI3 + ADC

HI, We are trying to use ADC with 12 Bit resolution and reference voltage 3.3V. Here we have connected R1=1 MOhm and R2=1.5 MOhm, voltage divider to Pin Number 32 (WB_A0). Below are our observation(s) a. analogRead() returns 1863 (i.e. adc_value) reading b. After converting 1863 to voltage gives as 2.5 volts using below formula V = (Vref * (adc_value) / max_adc_reading) / (R2/(R1 + R2)) V = (3.3 * (adc_value) / max) / (1.5/(1 + 1.5)) = 2.50V Can you please help me to understand at what p…

Please note that we have taken trial by using 10K and 15K resistor and now we are observing ADC readings equivalent to 3.3V.
However if I change input voltage (supply voltage) to 2.7V then ADC reading does not changes and voltage output calculation comes 3.3V…

Is there any other change do I need to do?
Please guide.

Regards,

Dinesh

[chansheunglong]

You are now using 2.7V, which there is no way a 3.3V refrence can be generated, so your calculation formula also need to be changed to use 2.7V instead of 3.3V

[carlrowan]

Hi @dinesh ,

Can you confirm what RUI3 version you use with AT+VER=?

The latest version is 4.0.1.

[dinesh (Dinesh Ananda Lohar)]

We are using RUI 3.4.11
Do we have to update to latest version or can we do this with 3.4.11?
Please advise.

[dinesh (Dinesh Ananda Lohar)]

Hi Carlrowan,

Greetings!

Please note that we have updated RUI version to 4.0.1.
We have observed same response as previous.
Can you please guide us further?

Regards,

Dinesh

[carlrowan]

Hi Dinesh,

I just like to confirm first your hardware setup.

1. You have a RAK3172 with constant 3.3V vref (2.7V is only on the adc input).
2. Voltage divider resistor is connection to WB_A0
3. You changed the input voltage going to WB_A0 to test if reading will be low.