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Integrate energy and charge over time, or compute current/voltage/power statistics, from a Joulescope JS220 energy-analyzer net. Requires the energy-analyzer net type.

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Import

from lager import Net, NetType

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Methods

MethodDescription
read_energy(duration)Integrate energy and charge over duration seconds
read_stats(duration)Compute mean/min/max/std for current, voltage, and power

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Method Reference

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Net.get(name, type=NetType.EnergyAnalyzer)

Get an energy analyzer net by name. 
from lager import Net, NetType

power = Net.get('POWER_METER', type=NetType.EnergyAnalyzer)
Parameters:
ParameterTypeDescription
namestrName of the energy-analyzer net
typeNetTypeMust be NetType.EnergyAnalyzer
Returns: Energy analyzer Net instance

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read_energy(duration)

Integrate current and power over duration seconds. 
result = power.read_energy(10.0)
print(f"Energy: {result['energy_wh'] * 1000:.3f} mWh")
print(f"Charge: {result['charge_ah'] * 1000:.3f} mAh")
Parameters:
ParameterTypeDescription
durationfloatIntegration window in seconds
Returns: dict with keys:
KeyTypeDescription
"energy_j"floatEnergy in joules
"energy_wh"floatEnergy in watt-hours
"charge_c"floatCharge in coulombs
"charge_ah"floatCharge in amp-hours
"duration_s"floatDuration that was requested

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read_stats(duration)

Compute mean, minimum, maximum, and standard deviation for current, voltage, and power over duration seconds. 
stats = power.read_stats(1.0)
print(f"Current: {stats['current']['mean'] * 1e6:.1f} uA (mean)")
print(f"Voltage: {stats['voltage']['mean']:.3f} V (mean)")
print(f"Power:   {stats['power']['mean'] * 1000:.3f} mW (mean)")
Parameters:
ParameterTypeDescription
durationfloatMeasurement window in seconds
Returns: dict with keys:
KeyTypeDescription
"current"dictCurrent statistics in amps
"voltage"dictVoltage statistics in volts
"power"dictPower statistics in watts
"duration_s"floatDuration that was requested
Each statistics sub-dict contains:
KeyTypeDescription
"mean"floatMean value
"min"floatMinimum value
"max"floatMaximum value
"std"floatStandard deviation

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Examples

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Energy Budget Check

from lager import Net, NetType

power = Net.get('DEVICE_POWER', type=NetType.EnergyAnalyzer)

result = power.read_energy(10.0)

energy_mwh = result['energy_wh'] * 1000
charge_mah = result['charge_ah'] * 1000

print(f"Energy: {energy_mwh:.3f} mWh")
print(f"Charge: {charge_mah:.3f} mAh")

if energy_mwh > 50:
    print("FAIL: Energy consumption exceeds budget")
else:
    print("PASS: Energy within budget")

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Sleep Current Verification

from lager import Net, NetType

power = Net.get('DEVICE_POWER', type=NetType.EnergyAnalyzer)

# Measure over 5 seconds for accuracy
stats = power.read_stats(5.0)

sleep_ua = stats['current']['mean'] * 1e6
supply_v = stats['voltage']['mean']

print(f"Sleep current: {sleep_ua:.1f} uA")
print(f"Supply voltage: {supply_v:.3f} V")

if sleep_ua < 100:
    print("PASS: Sleep current below 100 uA")
else:
    print(f"FAIL: Sleep current {sleep_ua:.1f} uA exceeds 100 uA limit")

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Battery Life Estimation

from lager import Net, NetType

power = Net.get('DEVICE_POWER', type=NetType.EnergyAnalyzer)

# Measure average current draw over a representative workload
stats = power.read_stats(30.0)

avg_current_ma = stats['current']['mean'] * 1000
avg_voltage_v = stats['voltage']['mean']

# Estimate from a 1000 mAh battery
battery_mah = 1000
hours = battery_mah / avg_current_ma if avg_current_ma > 0 else float('inf')

print(f"Average current: {avg_current_ma:.3f} mA")
print(f"Average voltage: {avg_voltage_v:.3f} V")
print(f"Estimated battery life: {hours:.1f} hours")

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Startup Energy Capture

from lager import Net, NetType

power = Net.get('DEVICE_POWER', type=NetType.EnergyAnalyzer)

# Capture energy consumed during device startup (2 seconds)
result = power.read_energy(2.0)

print(f"Startup energy: {result['energy_j'] * 1000:.2f} mJ")
print(f"Startup charge: {result['charge_c'] * 1000:.2f} mC")

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Current Spike Analysis

from lager import Net, NetType

power = Net.get('DEVICE_POWER', type=NetType.EnergyAnalyzer)

# Short window to capture peak current
stats = power.read_stats(1.0)

peak_ma = stats['current']['max'] * 1000
avg_ma = stats['current']['mean'] * 1000
std_ma = stats['current']['std'] * 1000

print(f"Peak current:    {peak_ma:.3f} mA")
print(f"Average current: {avg_ma:.3f} mA")
print(f"Std deviation:   {std_ma:.3f} mA")

# Flag if peak is more than 10x average (unexpected spike)
if peak_ma > avg_ma * 10:
    print("WARNING: Unexpected current spike detected")

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Supported Hardware

ManufacturerModelNet TypeUSB VID:PID
JoulescopeJS220energy-analyzer16d0:10ba
The energy-analyzer net type is exclusive to the Joulescope JS220. For instantaneous power readings (also available on Yocto-Watt), see Watt Meter.

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Notes

  • The Joulescope JS220 samples at high frequency; longer durations yield more accurate statistics
  • read_energy() and read_stats() block for the full duration before returning
  • The same physical JS220 device is shared between WattMeter and EnergyAnalyzer net roles — opening both net types for the same device is safe
  • Use lager instruments --box <box> to verify the JS220 is detected before running scripts