pcf8591: add ADC only implementation for I2C ADC/DAC (#690)

Signed-off-by: deadprogram <ron@hybridgroup.com>

examples/pcf8591/main.go

@@ -0,0 +1,28 @@
+// Connects to a pcf8591 ADC via I2C.
+package main
+
+import (
+	"machine"
+	"time"
+
+	"tinygo.org/x/drivers/pcf8591"
+)
+
+var (
+	i2c = machine.I2C0
+)
+
+func main() {
+	i2c.Configure(machine.I2CConfig{})
+	adc := pcf8591.New(i2c)
+	adc.Configure()
+
+	// get "CH0" aka "machine.ADC" interface to channel 0 from ADC.
+	p := adc.CH0
+
+	for {
+		val := p.Get()
+		println(val)
+		time.Sleep(50 * time.Millisecond)
+	}
+}

pcf8591/pcf8591.go

@@ -0,0 +1,84 @@
+// Package pcf8591 implements a driver for the PCF8591 Analog to Digital/Digital to Analog Converter.
+//
+// Datasheet: https://www.nxp.com/docs/en/data-sheet/PCF8591.pdf
+package pcf8591 // import "tinygo.org/x/drivers/pcf8591"
+
+import (
+	"machine"
+
+	"errors"
+
+	"tinygo.org/x/drivers"
+)
+
+// Device wraps PCF8591 ADC functions.
+type Device struct {
+	bus     drivers.I2C
+	Address uint16
+	CH0     ADCPin
+	CH1     ADCPin
+	CH2     ADCPin
+	CH3     ADCPin
+}
+
+// ADCPin is the implementation of the ADConverter interface.
+type ADCPin struct {
+	machine.Pin
+	d *Device
+}
+
+// New returns a new PCF8591 driver. Pass in a fully configured I2C bus.
+func New(b drivers.I2C) *Device {
+	d := &Device{
+		bus:     b,
+		Address: defaultAddress,
+	}
+
+	// setup all channels
+	d.CH0 = d.GetADC(0)
+	d.CH1 = d.GetADC(1)
+	d.CH2 = d.GetADC(2)
+	d.CH3 = d.GetADC(3)
+
+	return d
+}
+
+// Configure here just for interface compatibility.
+func (d *Device) Configure() {
+}
+
+// Read analog data from channel
+func (d *Device) Read(ch int) (uint16, error) {
+	if ch < 0 || ch > 3 {
+		return 0, errors.New("invalid channel for pcf8591 Read")
+	}
+
+	return d.GetADC(ch).Get(), nil
+}
+
+// GetADC returns an ADC for a specific channel.
+func (d *Device) GetADC(ch int) ADCPin {
+	return ADCPin{machine.Pin(ch), d}
+}
+
+// Get the current reading for a specific ADCPin.
+func (p ADCPin) Get() uint16 {
+	// TODO: also implement DAC
+	tx := make([]byte, 2)
+	tx[0] = byte(p.Pin)
+
+	rx := make([]byte, 2)
+
+	// The result from the measurement triggered by the first write,
+	// however, the second write is required to get the result.
+	// See section 8.4 "A/D Conversion" in the datasheet for more info
+	p.d.bus.Tx(p.d.Address, tx, rx)
+	p.d.bus.Tx(p.d.Address, tx, rx)
+
+	// scale result to 16bit value like other ADCs
+	return uint16(rx[1] << 8)
+}
+
+// Configure here just for interface compatibility.
+func (p ADCPin) Configure() {
+}

pcf8591/registers.go

@@ -0,0 +1,7 @@
+package pcf8591
+
+// PCF8591 Default Address
+const defaultAddress = 0x48
+
+// control bit for DAC
+const PCF8591_ENABLE_DAC = 0x40

smoketest.sh

@@ -106,6 +106,7 @@ tinygo build -size short -o ./build/test.hex -target=xiao ./examples/pcf8563/clk
 tinygo build -size short -o ./build/test.hex -target=xiao ./examples/pcf8563/time/
 tinygo build -size short -o ./build/test.hex -target=xiao ./examples/pcf8563/timer/
 tinygo build -size short -o ./build/test.hex -target=pico ./examples/qmi8658c/main.go
+tinygo build -size short -o ./build/test.hex -target=feather-rp2040 ./examples/pcf8591/
 tinygo build -size short -o ./build/test.hex -target=feather-m0 ./examples/ina260/main.go
 tinygo build -size short -o ./build/test.hex -target=nucleo-l432kc ./examples/aht20/main.go
 tinygo build -size short -o ./build/test.hex -target=feather-m4 ./examples/sdcard/console/