The most accurate answer is: Bluetooth module power consumption is a range, from microamps (µA) when sleeping to milliamps (mA) when actively transmitting.
To give you a practical understanding, let's break it down by the different operational states of a common Low Energy (BLE) module.
The Core Concept: Duty Cycle is King
Power consumption is all about the duty cycle-the percentage of time the radio is active versus asleep. A BLE module is designed to sleep for most of its life, waking up in brief, powerful bursts.
Power Consumption by Operational State
Here is a typical power profile for a modern BLE module (e.g., based on a Nordic nRF52 series chip):
| Operational State | Typical Current Draw | What's Happening & Why it Matters |
|---|---|---|
| Deep Sleep | 0.1 µA - 2 µA | The CPU and radio are completely off. Only a tiny trickle of power keeps the RAM memory alive and a low-power timer running. This is the baseline for long-term shelf life. |
| Standby / Idle | 2 µA - 10 µA | The core is sleeping, but it's ready to wake up very quickly in response to an event (like a timer or an external signal). |
| Advertising | 10 µA - 500 µA | The module wakes up, broadcasts a "I'm here!" packet, and goes back to sleep. Average current is highly dependent on the advertising interval. Advertising every 100ms will consume much more than advertising every 1 second. |
| Connected (Active) | 5 mA - 20 mA | The radio is actively transmitting or receiving data. This is the peak current, but it only lasts for a few hundred microseconds to a few milliseconds per connection event. |
| Connected (Sleeping between events) | 5 µA - 50 µA | This is the magic of BLE. In a connection, the module sleeps for almost the entire Connection Interval, only waking up for the tiny active period above. |
Key Takeaway: You cannot describe a module's consumption with one number. You must calculate an average current based on how much time it spends in each state.
Calculating Average Current & Battery Life
Let's do a simplified calculation for a common scenario: a BLE Sensor Tag that takes a temperature reading and sends it to a phone once per second.
Assumptions:
Connection Interval: 100 ms (a common value)
Active Time per event: 2 ms (transmitting the data)
Current in Active State: 10 mA
Current in Sleep State: 15 µA
Battery: 250 mAh coin cell (CR2032)
1. Calculate Duty Cycle:
The module is active for 2 ms every 100 ms.
Duty Cycle = (Active Time / Total Time) = (2 ms / 100 ms) = 2%
2. Calculate Average Current:
Average Current = (Duty Cycle × Active Current) + ((1 - Duty Cycle) × Sleep Current)
= (0.02 × 10,000 µA) + (0.98 × 15 µA)
= 200 µA + 14.7 µA
= ~215 µA (or 0.215 mA)
3. Estimate Battery Life:
Battery Life (hours) = Battery Capacity (mAh) / Average Current (mA)
= 250 mAh / 0.215 mA
≈ 1,163 hours → ~48 days
This example shows how a device with a peak current of 10 mA can still run for over a month on a small battery!
Comparison: BLE vs. Classic Bluetooth
It's crucial to distinguish between these two, as their power profiles are worlds apart:
| Bluetooth Type | Power Profile | Typical Use Cases |
|---|---|---|
| Bluetooth Low Energy (BLE) | "Peaky & Sleepy" - Very low average power (µA to mA range). Optimized for burst data. | IoT Sensors, Wearables, Beacons, Remote Controls. Battery life: months to years. |
| Classic Bluetooth (BR/EDR) | "Consistently Hungry" - Sustained high power (tens of mA). Optimized for continuous data streaming. | Audio Streaming (headphones, speakers), file transfer. Battery life: hours to days. |
Key Factors That Influence Power Consumption
Transmission Power: A module set to +8 dBm will consume significantly more power than at 0 dBm, but will have longer range.
Data Rate: Sending more data per connection event keeps the radio on for longer, increasing power.
Connection Parameters:
Connection Interval: Shorter intervals mean more frequent wake-ups, higher power. Longer intervals save power but increase latency.
Slave Latency: This is a "skip count" that allows a device to skip connection events if it has no data, dramatically reducing average power.
Peripheral Usage: If the module's internal MCU is also running your application code and sensors, that power must be added to the radio's consumption.
Conclusion
When evaluating a Bluetooth module's power consumption, don't just look at the "peak" or "sleep" numbers in the datasheet. Ask:
"What is the average current in my specific use case?"
Look for the vendor's application notes or online calculators that model power consumption for different scenarios (e.g., "1-second sensor update").
For the lowest power, choose a BLE module and work with your firmware engineer to optimize the connection parameters and maximize sleep time.
