Power-Down Mode - Battery Operation: How Barcode Scanners Survive on a Single Charge |
Subtitle: A Deep Dive into Sleep Modes, Wake-Up Sources, Power Management ICs, and Battery Life Optimization - with Real-World Examples from Symbol, Zebra, Honeywell, Datalogic, Texas Instruments, and Maxim Integrated |
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Opening Summary |
The modern barcode scanner is a wireless, battery-powered device. It must be ready to scan at a moment's notice, but it must also conserve power when it is idle. A scanner that runs out of battery in the middle of a shift is a scanner that fails its user. The key to long battery life is the power-down mode - a low-power state that the scanner enters when it is not in use. In this mode, most of the circuitry is turned off, and the scanner draws only a tiny current from the battery. When the user presses the trigger or presents an object, the scanner wakes up instantly and is ready to scan. |
This article is dedicated to power-down mode - the techniques that engineers use to extend battery life. We will explore the different levels of power reduction, from simple sleep modes to deep power-down states. We will examine the wake-up sources: the trigger, the object sensor, and the timer. We will look at the power management integrated circuits (PMICs) that control the power rails. We will see how major companies have implemented power-down mode in their products. We will examine Symbol's (now Zebra's) use of a simple sleep mode in the LS2208. We will explore Honeywell's use of a sophisticated PMIC in their imagers. We will examine Datalogic's use of an object-sense wake-up for their industrial scanners. We will also look at reference designs from Texas Instruments and Maxim Integrated. |
By the end of this journey, you will understand that power management is not an afterthought but a critical part of the scanner's design. You will see how the scanner balances performance and power consumption to achieve a long battery life. |
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Full Article |
Section 1: The Challenge - Balancing Performance and Power |
A barcode scanner must perform two contradictory tasks: it must scan quickly and accurately, and it must consume as little power as possible. The scanning process requires power - the illumination, the motor, the microcontroller, and the communication interface all draw current. The scanner must be able to deliver this power when it is scanning. But when it is idle, it should draw almost no power. |
The solution is power-down mode. In power-down mode, the scanner turns off most of its circuitry. It shuts down the illumination, the motor, and the communication interface. It puts the microcontroller into a low-power sleep state. The scanner draws only a tiny current (a few microamperes) to keep the wake-up circuitry alive. |
Section 2: The Sleep Mode - The Basic Power-Down State |
The sleep mode is the basic power-down state. In sleep mode, the microcontroller's CPU is turned off. The peripherals (timers, communication interfaces) are also turned off or put into a low-power state. The microcontroller retains its memory and its configuration. |
The sleep mode is typically entered by executing a 'sleep' instruction. The microcontroller wakes up from sleep when an interrupt occurs. |
Section 3: The Deep Sleep Mode - A Deeper Power-Down State |
The deep sleep mode is a more aggressive power-down state. In deep sleep mode, the microcontroller's memory is powered down. The microcontroller loses its state and must be reinitialized when it wakes up. |
The deep sleep mode consumes even less power than the sleep mode. |
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Section 4: The Wake-Up Sources - The Triggers |
The scanner must be able to wake up from power-down mode. The wake-up sources are the events that cause the scanner to wake up. The most common wake-up sources are: |
The Trigger: The user presses the trigger button. |
The Object Sensor: An object is detected in the scanner's field of view. |
The Timer: A periodic timer wakes up the scanner to check for pending tasks. |
Section 5: The Trigger - The Manual Wake-Up |
The trigger is the most common wake-up source. The user presses the trigger to start a scan. The trigger is connected to a GPIO pin of the microcontroller. The GPIO pin is configured to generate an interrupt when the trigger is pressed. The interrupt wakes up the microcontroller. |
Section 6: The Object Sensor - The Automatic Wake-Up |
The object sensor is an automatic wake-up source. The object sensor detects when an object is placed in front of the scanner. The object sensor is typically an infrared (IR) proximity sensor. The IR sensor emits a pulse of IR light and detects the reflection. When an object is detected, the sensor generates an interrupt that wakes up the microcontroller. |
The object sensor is used in presentation scanners, which are always on and ready to scan. |
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Section 7: The Timer - The Periodic Wake-Up |
The timer is a periodic wake-up source. The timer wakes up the scanner at regular intervals. The timer is used to check for pending tasks, such as battery monitoring or firmware updates. |
The timer is typically a low-power timer that runs in the background. |
Section 8: The Power Management IC - The Central Controller |
The power management IC (PMIC) is a dedicated chip that manages the scanner's power. The PMIC integrates the switching regulators, linear regulators, battery charger, and power management logic into a single chip. |
The PMIC controls the power to the various subsystems. It can turn off individual power rails to save power. The PMIC is controlled by the microcontroller. |
Section 9: Symbol's LS2208 - The Simple Sleep Mode |
Symbol's LS2208 uses a simple sleep mode. The LS2208 is a corded scanner, so it does not have a battery. However, it does have a sleep mode to reduce power consumption when it is not in use. The sleep mode is entered after a period of inactivity. The scanner wakes up when the trigger is pressed. |
The LS2208's sleep mode is a simple, effective solution. |
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Section 10: Honeywell's PMIC - The Advanced Power Management |
Honeywell's imagers use a sophisticated PMIC. The PMIC integrates the battery charger, the boost converter, and the linear regulators. The PMIC controls the power to the imager, the LEDs, and the microcontroller. |
The PMIC is controlled by the microcontroller. The microcontroller can put the scanner into a deep sleep mode, where the PMIC turns off all the power rails except the one supplying the microcontroller. |
Section 11: Datalogic's Object-Sense Wake-Up - The Automatic Wake-Up |
Datalogic's industrial scanners use an object-sense wake-up. The object-sense is an IR proximity sensor that detects when an object is placed in front of the scanner. The object-sense wakes up the scanner from a deep sleep mode. |
The object-sense wake-up allows the scanner to be always ready to scan, without consuming much power. |
Section 12: The Battery - The Energy Source |
The battery is the energy source for a portable scanner. The battery is typically a lithium-ion (Li-ion) or lithium-polymer (Li-Po) cell. The battery voltage is typically 3.7 to 4.2 volts. The battery capacity is typically 2000 to 4000 milliampere-hours (mAh). |
The battery life is determined by the battery capacity and the scanner's power consumption. |
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Section 13: The Battery Charger - The Recharging Circuit |
The battery charger is the circuit that recharges the battery. The battery charger is typically a switching regulator that converts the USB voltage or the AC mains voltage to the appropriate charging voltage. |
The battery charger is typically integrated into the PMIC. |
Section 14: The Battery Monitoring - The Fuel Gauge |
The battery monitoring circuit measures the battery's voltage and current. The battery monitoring circuit provides an estimate of the battery's remaining capacity. The estimate is typically displayed as a percentage. |
The battery monitoring is typically integrated into the PMIC. |
Section 15: The Power Consumption - The Current Budget |
The power consumption is the total current drawn by the scanner. The power consumption is the sum of the currents drawn by the various subsystems. |
The power consumption must be within the battery's capacity. The current budget is the maximum average current that the scanner can draw. |
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Section 16: The Active Mode - The Scanning Current |
The active mode is the mode where the scanner is scanning. The active mode current is the sum of the illumination current, the motor current, the microcontroller current, and the communication current. |
The active mode current is typically 100-500 milliamperes. |
Section 17: The Idle Mode - The Standby Current |
The idle mode is the mode where the scanner is powered on but not scanning. The idle mode current is the current drawn by the microcontroller and the power management circuitry. |
The idle mode current is typically 10-50 milliamperes. |
Section 18: The Sleep Mode - The Low-Power Current |
The sleep mode is the low-power state. The sleep mode current is the current drawn by the microcontroller's wake-up circuitry. |
The sleep mode current is typically 1-10 microamperes. |
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Section 19: The Deep Sleep Mode - The Ultra-Low-Power Current |
The deep sleep mode is the ultra-low-power state. The deep sleep mode current is the current drawn by the PMIC and the wake-up sources. |
The deep sleep mode current is typically 0.1-1 microampere. |
Section 20: The Wake-Up Time - The Latency |
The wake-up time is the time it takes for the scanner to wake up from sleep mode and be ready to scan. The wake-up time is typically 1-10 milliseconds for sleep mode and 10-100 milliseconds for deep sleep mode. |
The wake-up time must be short enough to not annoy the user. |
Section 21: The Power-Down Sequence - The Shutdown Process |
The power-down sequence is the process of entering sleep mode. The power-down sequence involves turning off the illumination, the motor, and the communication interface. It also involves saving the microcontroller's state. |
The power-down sequence must be carefully managed to avoid data loss. |
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Section 22: The Power-Up Sequence - The Startup Process |
The power-up sequence is the process of waking up from sleep mode. The power-up sequence involves restoring the microcontroller's state and turning on the illumination and the motor. |
The power-up sequence must be fast and reliable. |
Section 23: The Power Management in Microchip's Reference Design |
Microchip's reference design includes a power management example. The example shows how to enter sleep mode and wake up from sleep mode. |
Section 24: The Power Management in NXP's Reference Design |
NXP's reference design also includes a power management example. |
Section 25: The Power Management in STMicroelectronics' Reference Design |
STMicroelectronics' reference design includes a power management example. |
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Section 26: The Power Management and the Operating System |
The power management is typically integrated into the operating system or the firmware's main loop. |
Section 27: The Power Management and the User Interface |
The power management affects the user interface. The scanner may have a battery status LED or a display that shows the battery level. |
Section 28: The Power Management and the Communication |
The power management affects the communication. The scanner may turn off the communication interface to save power. |
Section 29: The Power Management and the Firmware |
The power management is a critical part of the firmware. The firmware must manage the power consumption. |
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Section 30: The Power Management and the Hardware |
The power management is also a critical part of the hardware. The hardware must support the power-down modes. |
Section 31: The Power Management and the Battery Life |
The power management directly affects the battery life. A longer battery life is achieved by a more aggressive power management. |
Section 32: The Power Management and the User Experience |
The power management affects the user experience. A scanner that wakes up quickly and has a long battery life is a good user experience. |
Section 33: The Power Management and the Cost |
The power management adds cost to the scanner. The PMIC and the battery monitoring circuit add to the component cost. |
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Section 34: The Power Management and the Reliability |
The power management affects the reliability. A reliable power management system ensures that the scanner operates correctly. |
Section 35: The Power Management and the Future - Energy Harvesting |
The future of power management is energy harvesting. Energy harvesting is the process of capturing energy from the environment. Energy harvesting could power the scanner without a battery. |
Section 36: The Power-Down Mode - A Summary of Best Practices |
Based on our exploration, let us summarize the best practices for implementing power-down mode in a barcode scanner: |
1. Use a PMIC: A PMIC simplifies the power management. |
2. Use Multiple Sleep Levels: Use sleep mode and deep sleep mode to optimize power consumption. |
3. Use Multiple Wake-Up Sources: Use the trigger, object sensor, and timer as wake-up sources. |
4. Optimize the Wake-Up Time: The wake-up time must be short. |
5. Monitor the Battery: Monitor the battery voltage and current. |
6. Test the Power Management: The power management must be tested under various conditions. |
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Final Summary |
Power-down mode is a critical feature for battery-powered barcode scanners. It allows the scanner to conserve power when it is not in use, extending the battery life. The scanner enters a low-power sleep mode and wakes up when the trigger is pressed or an object is detected. |
We have seen how major companies have implemented power-down mode. Symbol's LS2208 uses a simple sleep mode. Honeywell uses a sophisticated PMIC. Datalogic uses an object-sense wake-up. Microchip, NXP, and STMicroelectronics provide reference designs with power management examples. |
Power management is not an afterthought. It is a critical part of the scanner's design. By following the best practices, you can create a scanner that has a long battery life and a good user experience. |
*End of the expanded Chapter 33 article.* |
cs@easiersoft.com