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ads1x15: Add continuous reading, quality bias. Fix min/max values. (#307)

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pull/1/head
bezineb5 8 years ago committed by M-A
parent dcc7e03739
commit a74c97c8cd
2 changed files with 114 additions and 26 deletions
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108
experimental/devices/ads1x15/ads1x15.go
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@ -44,6 +44,16 @@ const (
Channel3 = 3
)
// ConversionQuality represents a request for a compromise between energy saving versus conversion quality.
type ConversionQuality int
const (
// SaveEnergy optimizes the power consumption of the ADC, at the expense of the quality by converting at the gihest rate possible.
SaveEnergy ConversionQuality = 0
// BestQuality will use the lowest suitable data rate to reduce the impact of the noise on the reading.
BestQuality ConversionQuality = 1
)
// Opts holds the configuration options.
type Opts struct {
I2cAddress uint16
@ -64,7 +74,7 @@ type Dev struct {
gainConfig map[int]uint16
dataRates map[int]uint16
gainVoltage map[int]physic.ElectricPotential
mutex *sync.Mutex
mutex sync.Mutex
}
// Reading is the result of AnalogPin.Read() (obviously not the case right now but this could be)
@ -80,6 +90,8 @@ type AnalogPin interface {
Range() (Reading, Reading)
// Read returns the current pin level.
Read() (Reading, error)
// ReadContinuous opens a channel and reads continuously
ReadContinuous() <-chan Reading
}
type ads1x15AnalogPin struct {
@ -87,6 +99,8 @@ type ads1x15AnalogPin struct {
query []byte
voltageMultiplier physic.ElectricPotential
waitTime time.Duration
requestedFrequency physic.Frequency
stop chan struct{}
}
// NewADS1015 creates a new driver for the ADS1015 (12-bit ADC)
@ -149,7 +163,6 @@ func newADS1x15(i i2c.Bus, opts *Opts) (l *Dev, err error) {
8: 512 * physic.MilliVolt,
16: 256 * physic.MilliVolt,
},
mutex: &sync.Mutex{},
}
return
@ -162,22 +175,23 @@ func (d *Dev) String() string {
// Halt returns true if devices is halted successfully
func (d *Dev) Halt() error { return nil }
func (d *Dev) PinForChannel(channel int, maxVoltage physic.ElectricPotential, minimumFrequency physic.Frequency) (pin AnalogPin, err error) {
// PinForChannel returns a pin able to measure the electric potential at the given channel
func (d *Dev) PinForChannel(channel int, maxVoltage physic.ElectricPotential, requestedFrequency physic.Frequency, conversionQuality ConversionQuality) (pin AnalogPin, err error) {
if err = d.checkChannel(channel); err != nil {
return
}
mux := channel + 0x04
return d.prepareQuery(mux, maxVoltage, minimumFrequency)
return d.prepareQuery(mux, maxVoltage, requestedFrequency, conversionQuality)
}
// PinForDifferenceOfChannels reads the difference in volts between 2 inputs: channelA - channelB.
// PinForDifferenceOfChannels returns a pin which measures the difference in volts between 2 inputs: channelA - channelB.
// diff can be:
// * Channel 0 - channel 1
// * Channel 0 - channel 3
// * Channel 1 - channel 3
// * Channel 2 - channel 3
func (d *Dev) PinForDifferenceOfChannels(channelA int, channelB int, maxVoltage physic.ElectricPotential, minimumFrequency physic.Frequency) (pin AnalogPin, err error) {
func (d *Dev) PinForDifferenceOfChannels(channelA int, channelB int, maxVoltage physic.ElectricPotential, requestedFrequency physic.Frequency, conversionQuality ConversionQuality) (pin AnalogPin, err error) {
var mux int
if err = d.checkChannel(channelA); err != nil {
@ -200,10 +214,10 @@ func (d *Dev) PinForDifferenceOfChannels(channelA int, channelB int, maxVoltage
return
}
return d.prepareQuery(mux, maxVoltage, minimumFrequency)
return d.prepareQuery(mux, maxVoltage, requestedFrequency, conversionQuality)
}
func (d *Dev) prepareQuery(mux int, maxVoltage physic.ElectricPotential, minimumFrequency physic.Frequency) (pin AnalogPin, err error) {
func (d *Dev) prepareQuery(mux int, maxVoltage physic.ElectricPotential, requestedFrequency physic.Frequency, conversionQuality ConversionQuality) (pin AnalogPin, err error) {
// Determine the most appropriate gain
gain, err := d.bestGainForElectricPotential(maxVoltage)
if err != nil {
@ -225,7 +239,7 @@ func (d *Dev) prepareQuery(mux int, maxVoltage physic.ElectricPotential, minimum
}
// Determine the most appropriate data rate
dataRate, err := d.bestDataRateForFrequency(minimumFrequency)
dataRate, err := d.bestDataRateForFrequency(requestedFrequency, conversionQuality)
if err != nil {
return
}
@ -272,6 +286,7 @@ func (d *Dev) prepareQuery(mux int, maxVoltage physic.ElectricPotential, minimum
query: query,
voltageMultiplier: voltageMultiplier,
waitTime: waitTime,
requestedFrequency: requestedFrequency,
}
return
@ -333,11 +348,30 @@ func (d *Dev) bestGainForElectricPotential(voltage physic.ElectricPotential) (be
}
// bestDataRateForFrequency returns the gain the most data rate to read samples at least at the requested frequency.
func (d *Dev) bestDataRateForFrequency(minimumFrequency physic.Frequency) (bestDataRate int, err error) {
func (d *Dev) bestDataRateForFrequency(requestedFrequency physic.Frequency, conversionQuality ConversionQuality) (bestDataRate int, err error) {
var max physic.Frequency
difference := physic.Frequency(math.MaxInt64)
currentBestDataRate := -1
// In order to save energy, we are going to select the fastest conversion rate, as explained in the ADS1115 specifications:
// 9.4.3 Duty Cycling For Low Power
// When searching for the best quality, we will select the slowest conversion rate which is still faster than the requested frequency.
var comparator func(physic.Frequency, physic.Frequency) bool
var difference physic.Frequency
switch conversionQuality {
case SaveEnergy:
// Saving energy requires the maximum data rate
difference = physic.Frequency(-1)
comparator = func(newDiff physic.Frequency, difference physic.Frequency) bool { return newDiff > difference }
case BestQuality:
// Best quality requires the minimum difference between the target and the capability
difference = physic.Frequency(math.MaxInt64)
comparator = func(newDiff physic.Frequency, difference physic.Frequency) bool { return newDiff < difference }
default:
err = fmt.Errorf("unknown value for ConversionQuality")
return
}
for key := range d.dataRates {
freq := physic.Frequency(key) * physic.Hertz
@ -346,8 +380,13 @@ func (d *Dev) bestDataRateForFrequency(minimumFrequency physic.Frequency) (bestD
max = freq
}
newDiff := freq - minimumFrequency
if newDiff >= 0 && newDiff < difference {
newDiff := freq - requestedFrequency
// Conversion rate slower than the requested frequency is not suitable
if newDiff < 0 {
continue
}
if comparator(newDiff, difference) {
difference = newDiff
currentBestDataRate = key
}
@ -372,9 +411,9 @@ func (d *Dev) checkChannel(channel int) (err error) {
// Range returns the maximum supported range [min, max] of the values.
func (p *ads1x15AnalogPin) Range() (minValue Reading, maxValue Reading) {
maxValue.V = p.voltageMultiplier
maxValue.Raw = 1 << 15
maxValue.Raw = math.MaxInt16
minValue.V = -maxValue.V
minValue.Raw = -maxValue.Raw
minValue.Raw = math.MinInt16
return
}
@ -384,6 +423,35 @@ func (p *ads1x15AnalogPin) Read() (Reading, error) {
return p.adc.executePreparedQuery(p.query, p.waitTime, p.voltageMultiplier)
}
func (p *ads1x15AnalogPin) ReadContinuous() <-chan Reading {
p.stopContinous()
reading := make(chan Reading)
p.stop = make(chan struct{})
go func() {
t := time.NewTicker(p.requestedFrequency.Duration())
defer t.Stop()
defer p.stopContinous()
defer close(reading)
for {
select {
case <-p.stop:
return
case <-t.C:
value, err := p.Read()
if err != nil {
// In continous mode, we'll ignore errors silently.
continue
}
reading <- value
}
}
}()
return reading
}
func (p *ads1x15AnalogPin) Name() string {
return fmt.Sprintf("%s pin", p.adc.name)
}
@ -397,9 +465,19 @@ func (p *ads1x15AnalogPin) Function() string {
}
func (p *ads1x15AnalogPin) Halt() error {
p.stopContinous()
return nil
}
func (p *ads1x15AnalogPin) String() string {
return p.Name()
}
func (p *ads1x15AnalogPin) stopContinous() {
if p.stop != nil {
close(p.stop)
p.stop = nil
}
return
}

16
experimental/devices/ads1x15/example_test.go
Unescape Escape View File

@ -34,17 +34,27 @@ func Example() {
}
// Obtain an analog pin from the ADC
pin, err := adc.PinForChannel(ads1x15.Channel0, 5*physic.Volt, 1*physic.Hertz)
pin, err := adc.PinForDifferenceOfChannels(ads1x15.Channel0, ads1x15.Channel3, 5*physic.Volt, 1*physic.Hertz, ads1x15.SaveEnergy)
if err != nil {
log.Fatalln(err)
}
defer pin.Halt()
// Read values from ADC.
value, err := pin.Read()
fmt.Println("Single reading")
reading, err := pin.Read()
if err != nil {
log.Fatalln(err)
}
fmt.Println(value)
fmt.Println(reading)
// Read values continously from ADC.
fmt.Println("Continuous reading")
c := pin.ReadContinuous()
for reading := range c {
fmt.Println(reading)
}
}

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