Add power meter.

README.md

@@ -101,7 +101,7 @@ A means of rendering multiple larger fonts to the SSD1306 OLED display. See
 [docs](./SSD1306/README.md).
 
 # mutex
-A class providing mutal exclusion enabling interrupt handlers and the main program to access shared
+A class providing mutual exclusion enabling interrupt handlers and the main program to access shared
 data in a manner which ensures data integrity.
 
 # watchdog
@@ -127,19 +127,20 @@ the same topic. Measures the round-trip delay. Adapt to suit your server address
 QOS (quality of service, 0 and 1 are supported). After 100 messages reports maximum and
 minimum delays.
 
-conn.py Connect in station mode using saved connection details where possible
+conn.py Connect in station mode using saved connection details where possible.
 
 # Rotary Incremental Encoder
 
-Classes for handling incremental rotary position encoders. Note that the Pyboard timers can
+Classes for handling incremental rotary position encoders. Note that the Pyboard
-do this in hardware. These samples cater for cases where that solution can't be used. The
+timers can do this in hardware. These samples cater for cases where that
-encoder_timed.py sample provides rate information by timing successive edges. In practice this
+solution can't be used. The encoder_timed.py sample provides rate information by
-is likely to need filtering to reduce jitter caused by imperfections in the encoder geometry.
+timing successive edges. In practice this is likely to need filtering to reduce
+jitter caused by imperfections in the encoder geometry.
 
 There are other algorithms but this is the simplest and fastest I've encountered.
 
-These were written for encoders producing TTL outputs. For switches, adapt the pull definition
+These were written for encoders producing TTL outputs. For switches, adapt the
-to provide a pull up or pull down as required.
+pull definition to provide a pull up or pull down as required.
 
 The `encoder.portable.py` version should work on all MicroPython platforms.
 Tested on ESP8266. Note that interrupt latency on the ESP8266 limits performance
@@ -159,6 +160,14 @@ of numbers following initialisation will always be the same.
 
 See the code for usage and timing documentation.
 
+# A design for a hardware power meter
+
+This uses a Pyboard to measure the power consumption of mains powered devices. 
+Unlike simple commercial devices it performs a true vector (phasor) measurement
+enabling it to provide information on power factor and to work with devices
+which generate as well as consume power. It uses the official LCD160CR display
+as a touch GUI interface. It is documented [here](./power/README.md).
+
 # License
 
 Any code placed here is released under the MIT License (MIT).  

power/README.md

@@ -0,0 +1,107 @@
+# A phasor power meter
+
+This measures the AC mains power consumed by a device. Unlike many cheap power
+meters it performs a vector measurement and can display true power, VA and
+phase. It can also plot snapshots of voltage and current waveforms. It can
+calculate average power consumption of devices whose consumption varies with
+time such as freezers and washing machines, and will work with devices capable
+of sourcing power into the grid. It supports full scale ranges of 30W to 3KW.
+
+[Images of device](./images/IMAGES.md)
+
+## Warning
+
+This project includes mains voltage wiring. Please don't attempt it unless you
+have the necessary skills and experience to do this safely.
+
+# Hardware Overview
+
+The file `SignalConditioner.fzz` includes the schematic and PCB layout for the
+device's input circuit. The Fritzing utility required to view and edit this is
+available (free) from [here](http://fritzing.org/download/).
+
+The unit includes a transformer with two 6VAC secondaries. One is used to power
+the device, the other to measure the line voltage. Current is measured by means
+of a current transformer SEN-11005 from SparkFun. The current output from this
+is converted to a voltage by means of an op-amp configured as a transconductance
+amplifier. This passes through a variable gain amplifier comprising two cascaded
+MCP6S91 programmable gain amplifiers, then to a two pole Butterworth low pass
+anti-aliasing filter. The resultant signal is presented to one of the Pyboard's
+shielded ADC's. The transconductance amplifier also acts as a single pole low
+pass filter.
+
+The voltage signal is similarly filtered with three matched poles to ensure
+that correct relative phase is maintained. The voltage channel has fixed gain.
+
+## PCB
+
+The PCB and schematic have an error in that the inputs of the half of opamp U4
+which handles the current signal are transposed.
+
+# Firmware Overview
+
+## Dependencies
+
+1. The `uasyncio` library.
+2. The official lcd160 driver `lcd160cr.py`.
+
+Also from the [lcd160cr GUI library](https://github.com/peterhinch/micropython-lcd160cr-gui.git)
+the following files:
+
+1. `lcd160_gui.py`.
+2. `font10.py`.
+3. `lcd_local.py`
+4. `constants.py`
+5. `lplot.py`
+
+## Configuration
+
+In my build the above plus `mains.py` are implemented as frozen bytecode. There
+is no SD card, the flash filesystem containing `main.py` and `mt.py`.
+
+If `mt.py` is deleted from flash and located on an SD card the code will create
+simulated sinewave samples for testing.
+
+## Design
+
+The code has not been optimised for performance, which in my view is adequate
+for the application.
+
+The module `mains.py` contains two classes, `Preprocessor` and `Scaling` which
+perform the data capture and analysis. The former acquires the data, normalises
+it and calculates normalised values of RMS voltage and current along with power
+and phase. `Scaling` controls the PGA according to the selected range and
+modifies the Vrms, Irms and P values to be in conventional units.
+
+The `Scaling` instance created in `mt.py` has a continuously running coroutine
+(`._run()`) which reads a set of samples, processes them, and executes a
+callback. Note that the callback function is changed at runtime by the GUI code
+(by `mains_device.set_callback()`). The iteration rate of `._run()` is about
+1Hz.
+
+The code is intended to offer a degree of noise immunity, in particular in the
+detection of voltage zero crossings. It operates by acquiring a set of 400
+sample pairs (voltage and current) as fast as standard MicroPython can achieve.
+On the Pyboard with 50Hz mains this captures two full cycles, so guaranteeing
+two positive going voltage zero crossings. The code uses an averaging algorithm
+to detect these (`Preprocessor.analyse()`) and populates four arrays of floats
+with precisely one complete cycle of data. The arrays comprise two pairs of
+current and voltage values, one scaled for plotting and the other scaled for
+measurement.
+
+Both pairs are scaled to a range of +-1.0 with any DC bias removed (owing to
+the presence of transformers this can only arise due to offsets in the
+circuitry and/or ADC's). DC removal facilitates long term integration.
+
+Plot data is further normalised so that current values exactly fill the +-1.0
+range. In other words plots are scaled so that the current waveform fills the
+Y axis with the X axis containing one full cycle. The voltage plot is made 10%
+smaller to avoid the visually confusing situation with a resistive load where
+the two plots coincide exactly.
+
+## Calibration
+
+This is defined by `Scaling.vscale` and `Scaling.iscale`. These values were
+initially calculated, then adjusted by comparing voltage and current readings
+with measurements from a calibrated meter. Voltage calibration in particular
+will probably need adjusting depending on the transformer characteristics.

power/images/IMAGES.md

@@ -0,0 +1,23 @@
+# Sample Images
+
+#Puhbuttons
+
+![Exterior](./outside.JPG)
+
+![Interior](./interior.JPG)
+Interior construction.
+
+![Microwave](./microwave.JPG)
+Microwave oven.
+![Plot](./plot.JPG)
+Microwave waveforms.
+
+![Integrate](./integrate.JPG)
+Integration screen.
+
+![Underrange](./underrange.JPG)
+Soldering iron on 3KW range.
+
+![Correct range](./correctrange.JPG)
+Same iron on 30W range
+

power/mains.py

@@ -0,0 +1,326 @@
+# mains.py Data collection and processing module for the power meter.
+
+# The MIT License (MIT)
+#
+# Copyright (c) 2017 Peter Hinch
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+
+from pyb import SPI, Pin, ADC
+from array import array
+from micropython import const
+from math import sin, cos, asin, pi, radians, sqrt
+import uasyncio as asyncio
+import gc
+gc.collect()
+
+# PINOUT
+# vadc X19
+# iadc X20
+# MOSI X8
+# MISO X7
+# SCK X6
+# CSN0 X5  First PGA
+# CSN1 X4  Second PGA
+
+# SAMPLING
+NSAMPLES = const(400)
+def arr_gen(n):
+    for _ in range(n):
+        yield 0
+
+isamples = array('h', arr_gen(NSAMPLES))
+vsamples = array('h', arr_gen(NSAMPLES))
+gc.collect()
+
+# HARDWARE
+vadc = ADC(Pin.board.X19)
+iadc = ADC(Pin.board.X20)
+
+spi = SPI(1)
+spi.init(SPI.MASTER, polarity = 0, phase = 0)
+
+# ************* Programmable Gain Amplifier *************
+
+class MCP6S91():
+    CHANNEL_ADDR = 0x41
+    GAIN_ADDR = 0x40
+    GAINVALS = (1, 2, 4, 5, 8, 10, 16, 32)
+    PINS = ('X5', 'X4')
+    def __init__(self, devno):
+        try:
+            self.csn = Pin(MCP6S91.PINS[devno], mode = Pin.OUT_PP)
+        except IndexError:
+            raise ValueError('MCP6S91 device no. must be 0 or 1.')
+        self.csn.value(1)
+        self.csn.value(0)
+        self.csn.value(1)  # Set state machine to known state
+        self.gain(1)
+
+    def gain(self, value):
+        try:
+            gainval = MCP6S91.GAINVALS.index(value)
+        except ValueError:
+            raise ValueError('MCP6S91 invalid gain {}'.format(value))
+        self.csn.value(0)
+        spi.send(MCP6S91.GAIN_ADDR)
+        spi.send(gainval)
+        self.csn.value(1)
+
+# Two cascaded MCP6S91 devices provide gains 1, 2, 5, 10, 20, 50, 100
+class PGA():
+    gvals = { 1 : (1, 1), 2 : (2, 1), 5 : (5, 1), 10 : (10, 1),
+             20 : (10, 2), 50 : (10, 5), 100 : (10, 10) }
+
+    def __init__(self):
+        self.amp0 = MCP6S91(0)
+        self.amp1 = MCP6S91(1)
+
+    def gain(self, value):
+        try:
+            g0, g1 = PGA.gvals[value]
+        except KeyError:
+            raise ValueError('PGA invalid gain {}'.format(value))
+        self.amp0.gain(g0)
+        self.amp1.gain(g1)
+
+# ************* Data Acquisition *************
+
+# Integer sample data put into vsamples and isamples global arrays.
+# Results are in range +-2047
+
+# SIMULATION PARAMETERS
+VPEAK = 0.545  # Relative to ADC FSD
+IPEAK = 0.6
+VPHASE = 0
+IPHASE = radians(45)
+
+def sample(simulate=False):
+    # Acquire just over 2 full cycles of AC
+    if simulate:
+        for n in range(NSAMPLES):
+            isamples[n] = int(2047 + IPEAK * 2047 * sin(4.2 * pi * n / NSAMPLES + IPHASE))
+            vsamples[n] = int(2047 + VPEAK * 2047 * sin(4.2 * pi * n / NSAMPLES + VPHASE))
+    else:
+        for n in range(NSAMPLES):
+            isamples[n] = iadc.read()
+            vsamples[n] = vadc.read()
+    for n in range(NSAMPLES):  # Normalise to -2047 to +2048
+        vsamples[n] -= 2047
+        if simulate:
+            isamples[n] -= 2047
+        else:
+            isamples[n] = 2047 - isamples[n]  # Sod's law. That's the way I wired the CT.
+
+# ************* Preprocessing *************
+
+# Filter data. Produce a single cycle of floating point data in two datasets.
+# Both are scaled -1.0 to +1.0.
+# Plot data is scaled such that the data exactly fits the range.
+# Output data is scaled such that DAC FS fits the range.
+
+class Preprocessor():
+    arraysize = const(NSAMPLES // 2)  # We acquire > 2 cycles
+    plotsize = const(50)
+    vplot = array('f', arr_gen(plotsize))  # Plot data
+    iplot = array('f', arr_gen(plotsize))
+    vscale = array('f', arr_gen(arraysize))  # Output data
+    iscale = array('f', arr_gen(arraysize))
+    def __init__(self, simulate, verbose):
+        self.avg_len = 4
+        self.avg_half = self.avg_len // 2
+        gc.collect()
+        self.simulate = simulate
+        self.verbose = verbose
+        self.overrange = False
+        self.threshold = 1997
+
+    def vprint(self, *args):
+        if self.verbose:
+            print(*args)
+
+    async def run(self):
+        self.overrange = False
+        sample(self.simulate)
+        return await self.analyse()
+
+    # Calculate average of avg_len + 1 numbers around a centre value. avg_len must be divisible by 2.
+    # This guarantees symmetry around the centre index.
+    def avg(self, arr, centre):
+        return sum(arr[centre - self.avg_half : centre + 1 + self.avg_half]) / (self.avg_len + 1)
+
+    # Filter a set of samples around a centre index in an array
+    def filt(self, arr, centre):
+        avg0 = self.avg(arr, centre - self.avg_half)
+        avg1 = self.avg(arr, centre + self.avg_half)
+        return avg0, avg1
+
+    async def analyse(self):
+        # Determine the first and second rising edge of voltage
+        self.overrange = False
+        nfirst = -1  # Index of 1st upward voltage transition
+        lastv = 0  # previous max
+        ovr = self.threshold  # Overrange threshold
+        for n in range(self.avg_len, NSAMPLES - self.avg_len + 1):
+            vavg0, vavg1 = self.filt(vsamples, n)
+            iavg0, iavg1 = self.filt(isamples, n)
+            vmax = max(vavg0, vavg1)
+            vmin = min(vavg0, vavg1)
+            imax = max(iavg0, iavg1)
+            imin = min(iavg0, iavg1)
+            if vmax > ovr or vmin < -ovr or imax > ovr or imin < -ovr:
+                self.overrange = True
+                self.vprint('overrange', vmax, vmin, imax, imin)
+            if nfirst == -1:
+                if vavg0 < 0 and vavg1 > 0 and abs(vmin) < lastv:
+                    nfirst = n if err > abs(abs(vmin) - lastv) else n - 1
+                    irising = iavg0 < iavg1  # Save current rising state for phase calculation
+            elif n > nfirst + NSAMPLES // 6:
+                if vavg0 < 0 and vavg1 > 0 and abs(vmin) < lastv:
+                    nsecond = n if err > abs(abs(vmin) - lastv) else n - 1
+                    break
+            lastv = vmax
+            err = abs(abs(vmin) - lastv)
+            yield
+        else:  # Should never occur because voltage should be present.
+            raise OSError('Failed to find a complete cycle.')
+        self.vprint(nfirst, nsecond, vsamples[nfirst], vsamples[nsecond], isamples[nfirst], isamples[nsecond])
+
+        # Produce datasets for a single cycle of V.
+        # Scale ADC FSD [-FSD 0 FSD] -> [-1.0 0 +1.0]
+        nelems = nsecond - nfirst + 1  # No. of samples in current cycle
+        p = 0
+        for n in range(nfirst, nsecond + 1):
+            self.vscale[p] = vsamples[n] / 2047
+            self.iscale[p] = isamples[n] / 2047
+            p += 1
+
+        # Remove DC offsets
+        sumv = 0.0
+        sumi = 0.0
+        for p in range(nelems):
+            sumv += self.vscale[p]
+            sumi += self.iscale[p]
+        meanv = sumv / nelems
+        meani = sumi / nelems
+        maxv = 0.0
+        maxi = 0.0
+        yield
+        for p in range(nelems):
+            self.vscale[p] -= meanv
+            self.iscale[p] -= meani
+            maxv = max(maxv, abs(self.vscale[p]))  # Scaling for plot
+            maxi = max(maxi, abs(self.iscale[p]))
+        yield
+        # Produce plot datasets. vplot scaled to avoid exact overlay of iplot
+        maxv = max(maxv * 1.1, 0.01)  # Cope with "no signal" conditions
+        maxi = max(maxi, 0.01)
+        offs = 0
+        delta = nelems / (self.plotsize -1)
+        for p in range(self.plotsize):
+            idx = min(round(offs), nelems -1)
+            self.vplot[p] = self.vscale[idx] / maxv
+            self.iplot[p] = self.iscale[idx] / maxi
+            offs += delta
+
+        if self.verbose:
+            for p in range(nelems):
+                print('{:7.3f} {:7.3f} {:7.3f} {:7.3f}'.format(
+                    self.vscale[p], self.iscale[p],
+                    self.vplot[round(p / delta)], self.iplot[round(p / delta)]))
+
+        phase = asin(self.iplot[0]) if irising else pi - asin(self.iplot[0])
+        yield
+        # calculate power, vrms, irms etc prior to scaling
+        us_vrms = 0
+        us_pwr = 0
+        us_irms = 0
+        for p in range(nelems):
+            us_vrms += self.vscale[p] * self.vscale[p]  # More noise-immune than calcuating from vmax * sqrt(2)
+            us_irms += self.iscale[p] * self.iscale[p]
+            us_pwr += self.iscale[p] * self.vscale[p]
+        us_vrms = sqrt(us_vrms / nelems)
+        us_irms = sqrt(us_irms / nelems)
+        us_pwr /= nelems
+        return phase, us_vrms, us_irms, us_pwr, nelems
+
+# Testing. Current provided to CT by 100ohm in series with secondary. Vsec = 7.8Vrms so i = 78mArms == 18W at 230Vrms.
+# Calculated current scaling:
+# FSD 3.3Vpp out = 1.167Vrms.
+# Secondary current Isec = 1.167/180ohm = 6.5mArms.
+# Ratio = 2000. Primary current = 12.96Arms.
+# At FSD iscale is +-1 = 0.707rms
+# Imeasured = us_irms * 12.96/(0.707  * self.pga_gain) = us_irms * 18.331 / self.pga_gain
+
+# Voltage scaling. Measured ADC I/P = 1.8Vpp == 0.545fsd pp == 0.386fsd rms
+# so vscale = 230/0.386 = 596
+
+class Scaling():
+    # FS Watts to PGA gain
+    valid_gains = (3000, 1500, 600, 300, 150, 60, 30)
+    vscale = 679  # These were re-measured with the new build. Zero load.
+    iscale = 18.0  # Based on measurement with 2.5KW resistive load (kettle)
+
+    def __init__(self, simulate=False, verbose=False):
+        self.cb = None
+        self.preprocessor = Preprocessor(simulate, verbose)
+        self.pga = PGA()
+        self.set_range(3000)
+        loop = asyncio.get_event_loop()
+        loop.create_task(self._run())
+
+    async def _run(self):
+        while True:
+            if self.cb is not None:
+                phase, us_vrms, us_irms, us_pwr, nelems = await self.preprocessor.run()  # Get unscaled values. Takes 360ms.
+                if self.cb is not None:  # May have changed during await
+                    vrms = us_vrms * self.vscale
+                    irms = us_irms * self.iscale / self.pga_gain
+                    pwr = us_pwr * self.iscale * self.vscale / self.pga_gain
+                    self.cb(phase, vrms, irms, pwr, nelems, self.preprocessor.overrange)
+            yield
+
+    def set_callback(self, cb=None):
+        self.cb = cb  # Set to None to pause acquisition
+
+    def set_range(self, val):
+        if val in self.valid_gains:
+            self.pga_gain = 3000 // val
+            self.pga.gain(self.pga_gain)
+        else:
+            raise ValueError('Invalid range. Valid ranges (W) {}'.format(self.valid_gains))
+
+    @property
+    def vplot(self):
+        return self.preprocessor.vplot
+
+    @property
+    def iplot(self):
+        return self.preprocessor.iplot
+
+def test():
+    def cb(phase, vrms, irms, pwr, nelems, ovr):
+        print('Phase {:5.1f}rad {:5.0f}Vrms {:6.3f}Arms {:6.1f}W Nsamples = {:3d}'.format(phase, vrms, irms, pwr, nelems))
+        if ovr:
+            print('Overrange')
+    s = Scaling(True, True)
+    s.set_range(300)
+    s.set_callback(cb)
+    loop = asyncio.get_event_loop()
+    loop.run_forever()

power/mt.py

@@ -0,0 +1,224 @@
+# mt.py Display module for the power meter
+
+# The MIT License (MIT)
+#
+# Copyright (c) 2017 Peter Hinch
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+
+import uasyncio as asyncio
+from mains import Scaling
+from constants import *
+from lcd160_gui import Button, Label, Screen, Dropdown, Dial, LED, ButtonList
+from lplot import CartesianGraph, Curve
+import font10
+from lcd_local import setup
+from utime import ticks_ms, ticks_diff
+from os import listdir
+
+if 'mt.py' in listdir('/flash'):
+    mains_device = Scaling() # Real
+#    mains_device = Scaling(True, False)  # Simulate
+else:  # Running on SD card - test setup
+    mains_device = Scaling(True, False)  # Simulate
+
+# STANDARD BUTTONS
+def fwdbutton(y, screen, text, color):
+    def fwd(button, screen):
+        Screen.change(screen)
+    return Button((109, y), font = font10, fontcolor = BLACK, callback = fwd,
+                  args = [screen], fgcolor = color, text = text)
+
+def backbutton():
+    def back(button):
+        Screen.back()
+    return Button((139, 0), font = font10, fontcolor = BLACK, callback = back,
+           fgcolor = RED,  text = 'X', height = 20, width = 20)
+
+def plotbutton(y, screen, color):
+    def fwd(button, screen):
+        Screen.change(screen)
+    return Button((139, y), font = font10, fontcolor = BLACK, callback = fwd,
+           args = [screen], fgcolor = color,  text = '~', height = 20, width = 20)
+
+# **** BASE SCREEN ****
+
+class BaseScreen(Screen):
+    def __init__(self):
+        super().__init__()
+        self.pwr_range = 3000
+# Buttons
+        fwdbutton(57, IntegScreen, 'Integ', CYAN)
+        fwdbutton(82, PlotScreen, 'Plot', YELLOW)
+# Labels
+        self.lbl_pf = Label((0, 31), font = font10, width = 75, border = 2, bgcolor = DARKGREEN, fgcolor = RED)
+        self.lbl_v = Label((0, 56), font = font10, width = 75, border = 2, bgcolor = DARKGREEN, fgcolor = RED)
+        self.lbl_i = Label((0, 81), font = font10, width = 75, border = 2, bgcolor = DARKGREEN, fgcolor = RED)
+        self.lbl_p = Label((0,106), font = font10, width = 75, border = 2, bgcolor = DARKGREEN, fgcolor = RED)
+        self.lbl_va = Label((80,106), font = font10, width = 79, border = 2, bgcolor = DARKGREEN, fgcolor = RED)
+# Dial
+        self.dial = Dial((109, 0), fgcolor = YELLOW, border = 2)
+# Dropdown
+        self.dropdown = Dropdown((0, 0), font = font10, width = 80, callback = self.cbdb,
+                                 elements = ('3000W', '600W', '150W', '60W', '30W'))
+        self.led = LED((84, 0), color = GREEN)
+        self.led.value(True)
+# Dropdown callback: set range
+    def cbdb(self, dropdown):
+        self.pwr_range = int(dropdown.textvalue()[: -1])  # String of form 'nnnW'
+        mains_device.set_range(self.pwr_range)
+#        print('Range set to', self.pwr_range, dropdown.value())
+
+    def reading(self, phase, vrms, irms, pwr, nelems, ovr):
+#        print(phase, vrms, irms, pwr, nelems)
+        self.lbl_v.value('{:5.1f}V'.format(vrms))
+        if ovr:
+            self.lbl_i.value('----')
+            self.lbl_p.value('----')
+            self.lbl_pf.value('----')
+            self.lbl_va.value('----')
+        else:
+            self.lbl_i.value('{:6.3f}A'.format(irms))
+            self.lbl_p.value('{:5.1f}W'.format(pwr))
+            self.lbl_pf.value('PF:{:4.2f}'.format(pwr /(vrms * irms)))
+            self.lbl_va.value('{:5.1f}VA'.format(vrms * irms))
+        self.dial.value(phase + 1.5708)  # Conventional phasor orientation.
+        if ovr:
+            self.led.color(RED)  # Overrange
+        elif abs(pwr) < abs(self.pwr_range) / 5:
+            self.led.color(YELLOW)  # Underrange
+        else:
+            self.led.color(GREEN)  # OK
+
+    def on_hide(self):
+        mains_device.set_callback(None)  # Stop readings
+
+    def after_open(self):
+        mains_device.set_callback(self.reading)
+
+# **** PLOT SCREEN ****
+
+class PlotScreen(Screen):
+    @staticmethod
+    def populate(curve, data):
+        xinc = 1 / len(data)
+        x = 0
+        for y in data:
+            curve.point(x, y)
+            x += xinc
+
+    def __init__(self):
+        super().__init__()
+        backbutton()
+        Label((142, 45), font = font10, fontcolor = YELLOW, value = 'V')
+        Label((145, 70), font = font10, fontcolor = RED, value = 'I')
+        g = CartesianGraph((0, 0), height = 127, width = 135, xorigin = 0) # x >= 0
+        Curve(g, self.populate, args = (mains_device.vplot,))
+        Curve(g, self.populate, args = (mains_device.iplot,), color = RED)
+
+# **** INTEGRATOR SCREEN ****
+
+class IntegScreen(Screen):
+    def __init__(self):
+        super().__init__()
+# Buttons
+        backbutton()
+        plotbutton(80, PlotScreen, YELLOW)
+# Labels
+        self.lbl_p = Label((0, 0), font = font10, width = 78, border = 2, bgcolor = DARKGREEN, fgcolor = RED)
+        Label((90, 4), font = font10, value = 'Power')
+        self.lbl_pmax = Label((0, 30), font = font10, width = 78, border = 2, bgcolor = DARKGREEN, fgcolor = RED)
+        Label((90, 34), font = font10, value = 'Max')
+        self.lbl_pin = Label((0, 55), font = font10, width = 78, border = 2, bgcolor = DARKGREEN, fgcolor = RED)
+        self.lbl_pmin = Label((0, 80), font = font10, width = 78, border = 2, bgcolor = DARKGREEN, fgcolor = RED)
+        Label((90, 84), font = font10, value = 'Min')
+        self.lbl_w_hr = Label((0,105), font = font10, width = 78, border = 2, bgcolor = DARKGREEN, fgcolor = RED)
+        self.lbl_t = Label((88, 105), font = font10, width = 70, border = 2, bgcolor = DARKGREEN, fgcolor = RED)
+
+        table = [
+            {'fgcolor' : GREEN, 'text' : 'Max Gen', 'args' : (True,)},
+            {'fgcolor' : BLUE, 'text' : 'Mean', 'args' : (False,)},
+        ]
+        bl = ButtonList(self.buttonlist_cb)
+        for t in table: # Buttons overlay each other at same location
+            bl.add_button((90, 56), width = 70, font = font10, fontcolor = BLACK, **t)
+        self.showmean = False
+        self.t_reading = None  # Time of last reading
+        self.t_start = None  # Time of 1st reading
+        self.joules = 0  # Cumulative energy
+        self.overrange = False
+        self.wmax = 0  # Max power out
+        self.wmin = 0  # Max power in
+        self.pwr_min = 10000 # Power corresponding to minimum absolute value
+
+    def reading(self, phase, vrms, irms, pwr, nelems, ovr):
+        self.wmax = max(self.wmax, pwr)
+        self.wmin = min(self.wmin, pwr)
+        if abs(pwr) < abs(self.pwr_min):
+            self.pwr_min = pwr
+        if ovr:
+            self.overrange = True
+        t_last = self.t_reading # Time of last reading (ms)
+        self.t_reading = ticks_ms()
+        if self.t_start is None:  # 1st reading
+            self.t_start = self.t_reading  # Time of 1st reading
+        else:
+            self.joules += pwr * ticks_diff(self.t_reading, t_last) / 1000
+
+        secs_since_start = ticks_diff(self.t_reading, self.t_start) / 1000  # Runtime
+        mins, secs = divmod(int(secs_since_start), 60)
+        hrs, mins = divmod(mins, 60)
+        self.lbl_t.value('{:02d}:{:02d}:{:02d}'.format(hrs, mins, secs))
+        if ovr:
+            self.lbl_p.value('----')
+        else:
+            self.lbl_p.value('{:5.1f}W'.format(pwr))
+
+        if self.showmean:
+            self.lbl_pin.value('{:5.1f}W'.format(self.joules / max(secs_since_start, 1)))
+        else:
+            self.lbl_pin.value('{:5.1f}W'.format(self.wmin))
+
+        self.lbl_pmin.value('{:5.1f}W'.format(self.pwr_min))
+        if self.overrange:  # An overrange occurred during the measurement
+            self.lbl_w_hr.value('----')
+            self.lbl_pmax.value('----')
+        else:
+            self.lbl_pmax.value('{:5.1f}W'.format(self.wmax))
+            units = self.joules / 3600
+            if units < 1000:
+                self.lbl_w_hr.value('{:6.0f}Wh'.format(units))
+            else:
+                self.lbl_w_hr.value('{:6.2f}KWh'.format(units / 1000))
+
+    def buttonlist_cb(self, button, arg):
+        self.showmean = arg
+
+    def on_hide(self):
+        mains_device.set_callback(None)  # Stop readings
+
+    def after_open(self):
+        mains_device.set_callback(self.reading)
+
+def test():
+    print('Running...')
+    setup()
+    Screen.change(BaseScreen)
+
+test()