Hi Frank, On Tue, Sep 24, 2024 at 11:09:51AM -0400, Frank Li wrote: > On Tue, Sep 24, 2024 at 01:40:53PM +0200, Francesco Dolcini wrote: > > From: João Paulo Gonçalves <joao.goncalves@xxxxxxxxxxx> > > > > Add Toradex Verdin Ivy carrier board support. One notable feature of Ivy > > is the analog inputs. These inputs are multiplexed, allowing the same > > input to measure either voltage or current. For current measurements, > > a GPIO switch enables or disables the shunt resistor. This process is > > automatically managed by the Linux kernel using the IIO and MUX > > subsystems. Voltage measurement is always enabled, but the voltage > > measured by the ADC is scaled by a cascade voltage divider. In the > > device tree, the equivalent gain of the voltage divider is used, which > > can be calculated as follows: > > > > ------------ > > + | > > .-. > > R1=30K | | > > | | > > '-' > > |------------------- > > Analog Input (AIN) | | > > .-. .-. > > R2=10K | | R3=30K | | > > | | | | > > '-' '-' > > | | > > | |-------- > > | .-. + > > | R4=10K | | > > | | | ADC Input (Channels 0 and 1) > > | '-' > > - | | - > > -----------| |-------- > > === === > > GND GND > > > > Vin = Analog Input (AIN) > > Vout = ADC Input > > Rth = Thevenin Equiv. Resistance > > Vth = Thevenin Equiv. Voltage > > RL = Load Resistor > > > > R1 = 30K, R2 = 10K, R3 = 30K, R4 = 10K > > RL = R4 = 10K > > > > Rth = (R1 // R2) + R3 = 37500 Ohms > > Vth = (Vin * R2) / (R1 + R2) = Vin/4; > > Vout = (Vth * RL)/ (Rth + RL) = Vth/4.75 = Vin/19 > > Gain = Vout/Vin = 1/19 > > which properties related these value? The gain value is used on the "ain1_voltage_unmanaged" node for the full-ohms and output-ohms properties. Best Regards, João Paulo Gonçalves
