Voltage divider
|
===============
|
|
When an io-channel measures the midpoint of a voltage divider, the
|
interesting voltage is often the voltage over the full resistance
|
of the divider. This binding describes the voltage divider in such
|
a curcuit.
|
|
Vin ----.
|
|
|
.-----.
|
| R |
|
'-----'
|
|
|
+---- Vout
|
|
|
.-----.
|
| Rout|
|
'-----'
|
|
|
GND
|
|
Required properties:
|
- compatible : "voltage-divider"
|
- io-channels : Channel node of a voltage io-channel measuring Vout.
|
- output-ohms : Resistance Rout over which the output voltage is measured.
|
See full-ohms.
|
- full-ohms : Resistance R + Rout for the full divider. The io-channel
|
is scaled by the Rout / (R + Rout) quotient.
|
|
Example:
|
The system voltage is circa 12V, but divided down with a 22/222
|
voltage divider (R = 200 Ohms, Rout = 22 Ohms) and fed to an ADC.
|
|
sysv {
|
compatible = "voltage-divider";
|
io-channels = <&maxadc 1>;
|
|
/* Scale the system voltage by 22/222 to fit the ADC range. */
|
output-ohms = <22>;
|
full-ohms = <222>; /* 200 + 22 */
|
};
|
|
&spi {
|
maxadc: adc@0 {
|
compatible = "maxim,max1027";
|
reg = <0>;
|
#io-channel-cells = <1>;
|
interrupt-parent = <&gpio5>;
|
interrupts = <15 IRQ_TYPE_EDGE_RISING>;
|
spi-max-frequency = <1000000>;
|
};
|
};
|
