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Measure power consumption from watt meter nets. Supports Yocto-Watt, Joulescope JS220, and Nordic PPK2 hardware.
Import
from lager import Net, NetType
Methods
| Method | Hardware | Description |
|---|
read() | All | Read power in watts |
read_current() | Joulescope JS220, Nordic PPK2 | Read current in amps |
read_voltage() | Joulescope JS220, Nordic PPK2 | Read voltage in volts |
read_all() | Joulescope JS220, Nordic PPK2 | Read current, voltage, and power in a single operation |
Method Reference
Net.get(name, type=NetType.WattMeter)
Get a watt meter net by name.
from lager import Net, NetType
power = Net.get('POWER_METER', type=NetType.WattMeter)
| Parameter | Type | Description |
|---|
name | str | Name of the watt meter net |
type | NetType | Must be NetType.WattMeter |
read()
Read the current power consumption. Available on all watt meter hardware.
watts = power.read()
print(f"Power: {watts}W")
float - Power in watts
read_current()
Read the current in amps. Joulescope JS220 and Nordic PPK2.
amps = power.read_current()
print(f"Current: {amps}A")
float - Current in amps
read_voltage()
Read the voltage in volts. Joulescope JS220 and Nordic PPK2.
volts = power.read_voltage()
print(f"Voltage: {volts}V")
float - Voltage in volts
read_all()
Read current, voltage, and power in a single atomic measurement. Joulescope JS220 and Nordic PPK2. This is more efficient than calling read_current(), read_voltage(), and read() separately, as all values come from the same sample window.
measurements = power.read_all()
print(f"Current: {measurements['current']}A")
print(f"Voltage: {measurements['voltage']}V")
print(f"Power: {measurements['power']}W")
dict with keys:
| Key | Type | Description |
|---|
"current" | float | Current in amps |
"voltage" | float | Voltage in volts |
"power" | float | Power in watts |
Examples
Basic Power Reading
from lager import Net, NetType
power = Net.get('DEVICE_POWER', type=NetType.WattMeter)
watts = power.read()
print(f"Power consumption: {watts:.3f}W")
Joulescope Full Measurement
from lager import Net, NetType
power = Net.get('DEVICE_POWER', type=NetType.WattMeter)
# Read all measurements at once (Joulescope JS220 and Nordic PPK2)
data = power.read_all()
print(f"Voltage: {data['voltage']:.3f}V")
print(f"Current: {data['current']:.6f}A")
print(f"Power: {data['power']:.3f}W")
Power Profiling
from lager import Net, NetType
import time
power = Net.get('DEVICE_POWER', type=NetType.WattMeter)
measurements = []
# Take 60 seconds of measurements
for i in range(60):
watts = power.read()
measurements.append(watts)
print(f"[{i:3d}s] {watts:.3f}W")
time.sleep(1)
# Statistics
avg = sum(measurements) / len(measurements)
max_p = max(measurements)
min_p = min(measurements)
print(f"\nAverage: {avg:.3f}W")
print(f"Maximum: {max_p:.3f}W")
print(f"Minimum: {min_p:.3f}W")
Battery Life Estimation
from lager import Net, NetType
import time
power = Net.get('POWER', type=NetType.WattMeter)
# Average over multiple readings
readings = []
for _ in range(10):
readings.append(power.read())
time.sleep(0.1)
avg_power = sum(readings) / len(readings)
# Estimate battery life (1000mAh @ 3.7V = 3.7Wh)
battery_wh = 3.7
hours = battery_wh / avg_power if avg_power > 0 else float('inf')
print(f"Average power: {avg_power:.3f}W")
print(f"Est. battery life: {hours:.1f} hours")
Power Limit Verification
from lager import Net, NetType
import time
def verify_power_limits(min_watts, max_watts):
power = Net.get('DEVICE_POWER', type=NetType.WattMeter)
# Average multiple readings
readings = []
for _ in range(10):
readings.append(power.read())
time.sleep(0.1)
avg = sum(readings) / len(readings)
if min_watts <= avg <= max_watts:
print(f"PASS: {avg:.3f}W in range [{min_watts}, {max_watts}]")
return True
else:
print(f"FAIL: {avg:.3f}W outside range [{min_watts}, {max_watts}]")
return False
# Test
verify_power_limits(0.1, 5.0)
Sleep Current Verification (Joulescope)
from lager import Net, NetType
import time
power = Net.get('DEVICE_POWER', type=NetType.WattMeter)
# Put device in sleep mode (external trigger)
# set_device_sleep_mode()
time.sleep(2) # Wait for stabilization
# Use read_all() for atomic measurement (Joulescope JS220)
data = power.read_all()
sleep_current_ua = data['current'] * 1e6
print(f"Sleep voltage: {data['voltage']:.3f}V")
print(f"Sleep current: {sleep_current_ua:.1f}uA")
print(f"Sleep power: {data['power']:.6f}W")
if sleep_current_ua < 100:
print("PASS: Sleep current below 100uA")
else:
print("FAIL: Sleep current exceeds limit")
Supported Hardware
| Manufacturer | Model | Measurement | Features |
|---|
| Yoctopuce | Yocto-Watt | Power only | Instantaneous reading |
| Joulescope | JS220 | Power, voltage, current | 0.1s averaged, atomic multi-measurement |
| Nordic Semiconductor | PPK2 | Power, voltage, current | 0.3s averaged, source mode constant voltage |
Hardware Feature Comparison
| Feature | Yocto-Watt | Joulescope JS220 | Nordic PPK2 |
|---|
read() (power) | Yes | Yes | Yes |
read_current() | No | Yes | Yes |
read_voltage() | No | Yes | Yes |
read_all() | No | Yes | Yes |
| Measurement method | Instantaneous | 0.1s averaged | 0.3s averaged |
| Device selection | Channel-based | Serial number-based | Serial number-based |
Notes
- Power is returned in watts (W)
- Joulescope JS220 averages measurements over 0.1 seconds for higher precision
- Nordic PPK2 averages measurements over 0.3 seconds; operates in source mode (supplies a configurable voltage 0.8–5V), so voltage readings reflect the configured value, not an independent measurement
read_current(), read_voltage(), and read_all() are available on the Joulescope JS220 and Nordic PPK2; calling them on a Yocto-Watt will raise an error- For current on Yocto-Watt: calculate from power and known voltage (I = P / V)
- Use multiple readings and averaging for stability
- Allow settling time after device state changes
