Request a voltage

What this example shows

The sketch asks the charger for a new voltage over I2C, once, at start-up. It prints whether the charger switched, and if it did, it prints the voltage and current every second. The voltage to ask for is set by REQUEST_VOLTAGE, 20 V in the example; it must be 5, 9, 12, 15, 18 or 20.

A successful request changes the voltage on VOUT. Disconnect anything on VOUT that cannot take the voltage you request before you run the sketch.

Wire SDA, SCL and GND to your controller's I2C pins as in the Quick Start, and plug a charger into the board with the slide switch on.

The example code

This is RequestVoltage.ino from the pinned library, without its header comment. The sketch itself is exactly as shipped.

Select Board

RequestVoltage.ino

#include "HUSB238-SOLDERED.h"

Husb238 husb238;

// Voltage to request from the source, one of 5, 9, 12, 15, 18, 20
#define REQUEST_VOLTAGE 20

bool requestOk = false;

void setup()
{
    Serial.begin(115200);
    husb238.begin();

    Serial.print("Requesting ");
    Serial.print(REQUEST_VOLTAGE);
    Serial.println(" V...");

    switch (husb238.requestPD(REQUEST_VOLTAGE))
    {
    case HUSB238_REQUEST_OK:
        Serial.println("Source switched voltage successfully");
        requestOk = true;
        break;
    case HUSB238_REQUEST_UNSUPPORTED_VOLTAGE:
        Serial.println("Invalid voltage value, use 5/9/12/15/18/20");
        break;
    case HUSB238_REQUEST_NOT_OFFERED:
        Serial.println("Charger does not support this voltage");
        break;
    case HUSB238_REQUEST_REJECTED:
        Serial.println("Charger rejected the request");
        break;
    }
}

void loop()
{
    if (!requestOk)
        return;

    Serial.print("Voltage: ");
    Serial.print(husb238.getPDSrcVoltage());
    Serial.print(" V, current: ");
    Serial.print(husb238.getPDSrcCurrent());
    Serial.println(" A");

    delay(1000);
}

Expected result, with a 65 W USB-C PD charger that offers 20 V at 3.25 A, in the Serial Monitor at 115200 baud:

Serial MonitorAutoscrollShow timestampNewline115200 baud

Message (Enter to send message to the board)

Requesting 20 V...
Source switched voltage successfully
Voltage: 20.00 V, current: 3.25 A
Voltage: 20.00 V, current: 3.25 A
Voltage: 20.00 V, current: 3.25 A

After the first two lines, a line starting with Voltage: appears every second, with the agreed voltage in volts and the charger's current in amps. If the request fails, the second line is one of Invalid voltage value, use 5/9/12/15/18/20, Charger does not support this voltage or Charger rejected the request, and nothing more is printed.

Functions used

Husb238(uint8_t _address = HUSB238_I2C_ADDR, TwoWire &_wire = Wire)returns None

Creates the HUSB238 object. It only stores the I2C address and the Wire port. Nothing is read from or written to the chip until the first read or request function.

ReturnsConstructor; no return value.

Parameters

Name	Type	Description
_address	uint8_t	I2C address. Defaults to HUSB238_I2C_ADDR, which is 0x08, the board's fixed address.
_wire	TwoWire &	The Wire interface to use. Defaults to Wire.

begin()returns void

Starts I2C communication by calling begin() on the Wire port the object was created with.

ReturnsNothing.

requestPD(float voltage)returns husb238RequestResult_t

Asks the source to switch to the given voltage. It first checks that the value is one of the six the HUSB238 can request and that the source advertises it. Then it writes the request to the chip, waits 300 ms and reads back the source's response.

ReturnsThe outcome of the request, one of the four values in the table below.

Parameters

Name	Type	Description
voltage	float	Voltage to request: 5, 9, 12, 15, 18 or 20.

Return value	Meaning
HUSB238_REQUEST_OK	The source switched voltage successfully.
HUSB238_REQUEST_UNSUPPORTED_VOLTAGE	The voltage is not one of 5, 9, 12, 15, 18 or 20. Nothing is sent.
HUSB238_REQUEST_NOT_OFFERED	The source does not advertise this voltage. The library reads the source's offer for it and writes nothing.
HUSB238_REQUEST_REJECTED	The request was sent, but the source did not report success.

getPDSrcVoltage()returns float

Reads the currently negotiated source voltage from the PD_STATUS0 register.

ReturnsThe voltage in volts: 5, 9, 12, 15, 18 or 20, or 0 if no source is attached.

getPDSrcCurrent()returns float

Reads the source's maximum current for the negotiated contract from the PD_STATUS0 register.

ReturnsThe current in amps, one of the HUSB238's steps from 0.5 to 5.0 A.

Putting it together

setup() sends the request once, so reset the controller to send it again. The switch turns the result of requestPD() into a message, and only HUSB238_REQUEST_OK sets requestOk. Until it is set, loop() returns at once and prints nothing. Once it is, getPDSrcVoltage() and getPDSrcCurrent() show the new contract every second.

To ask for another voltage, change REQUEST_VOLTAGE to 5, 9, 12, 15, 18 or 20 and upload the sketch again.

SourceOpen the verified Arduino exampleView the exact source used by this page.examples/RequestVoltage/RequestVoltage.ino