Disabling HDMI

If you are using a Raspberry Pi in a headless configuration (using a remote device to control it), turning off the HDMI port is a no-pain way to save power (about 25mA). Per Jeff Geerling, you can disable HDMI in two ways. From the command line (Raspbian or similar Linux distros):

/usr/bin/tvservice -o                

To disable HDMI at boot, edit /etc/rc.local and add

/usr/bin/tvservice -o

To reenable HDMI from the command line:

/usr/bin/tvservice -p                

Disabling Onboard LEDs

Individual LEDs can be disabled from the command line (see https://www.jeffgeerling.com/blogs/jeff-geerling/controlling-pwr-act-leds-raspberry-pi ). For Raspberry Pi 2, B+, and A+, run sudo nano /boot/config.txt and add these commands to disable both LEDs at boot:

# Disable the ACT LED.
dtparam=act_led_trigger=none
dtparam=act_led_activelow=off

# Disable the PWR LED.
dtparam=pwr_led_trigger=none
dtparam=pwr_led_activelow=off

Save changes, exit, and reboot.

With Raspberry Pi Zero, there’s only one LED to disable. It can be disabled from the command line, or at boot time. Run sudo nano /boot/config.txt and add these commands:

# Disable the ACT LED on the Pi Zero.
dtparam=act_led_trigger=none
dtparam=act_led_activelow=on

The LEDs on the Raspberry Pi 3 appear to have different default behaviors depending upon the specific Linux distro used. For details, see the discussion thread at www.jeffgeerling.com/blogs/jeff-geerling/controlling-pwr-act-leds-raspberry-pi .

Enabling Login and Control via TTY

Disabling USB ports on the B+, Pi 2, and Pi 3 reduces power consumption significantly, increasing runtime by several hours when using the Pi for periodic photo captures. Unfortunately, these models implement their UBS ports though a hub that also controls the Ethernet port (see https://babaawesam.com/2014/01/24/power-saving-tips-for-raspberry-pi/ ). Consequently, these steps must be performed before you can boot your system without USB/Ethernet support :

1. Enable Serial with raspi-config or the equivalent in Raspbian with PIXEL or other GUIs

2. Connect a USB to TTL cable (Figure 10-2) from your PC or MacOS computer’s USB port to the appropriate pins on the GPIO bus:

   • Green: connect to RXD (receive) pin - PIN 10 (physical)/ GPIO 14

   • White: connect to TXD (transmit) pin - PIN 8 (physical) / GPIO 15

   • Black: connect to GND (ground) pin - PIN 6 or 14 (physical)

   • Red: connect to 5V power pin - PIN 2 or 4 (physical) only if the Micro-USB power cable is NOT connected to the Raspberry Pi (see inset in Figure 10-2)

     

     Figure 10-2. A USB-to-TTL (debug) cable enables you to connect to your Raspberry Pi’s GPIO pins for remote control via TTY. The inset (lower right) shows the use of the red power cable in place of the normal Micro-USB power connector on the Raspberry Pi.

3. Install the appropriate driver for your USB to TTY cable on your PC or MacOS computer. Older cables use the Prolific 2303 chipset driver, while newer cables use the SiLabs CP210X chipset. If you are not certain which cable you use, install both. Most Linux distros already have the appropriate driver installed.

4. You can connect directly to your Raspberry Pi from MacOS’s terminal with one of these commands (depending upon the cable’s chipset):

   screen /dev/cu.PL2303* 115200

   OR

   screen /dev/cu.usbserial 115200

5. To connect from another Linux computer, use

   sudo screen /dev/ttyUSB0 115200

6. To connect from Windows, download and install PuTTY ( www.chiark.greenend.org.uk/~sgtatham/putty/latest.html ):

   1. Use Windows Device Manager to determine the COM port used by the USB-TTL cable.

   2. Use the Serial Line connection option in PuTTY , specifying the COM port used by the cable and the speed of 115200 (Figure 10-3).

      

      Figure 10-3. Connecting to the Raspberry Pi with PuTTY. Replace COMX with the actual COM port number as reported by Windows Device Manager.

7. Log into your Raspberry Pi when prompted.

Disabling USB Hub and Ethernet

After booting and logging into your Raspberry Pi via TTL, use the following commands to disable the USB hub which also controls Ethernet:

#!/bin/bash
#Code to stop
/etc/init.d/networking stop
echo 0 > /sys/devices/platform/bcm2708_usb/buspower;
echo "Bus power stopping"

#!/bin/bash
#Code to start
echo 1 > /sys/devices/platform/bcm2708_usb/buspower;
echo "Bus power starting"
sleep 2;
/etc/init.d/networking start

If this script does not work, see https://babaawesam.com/2014/01/24/power-saving-tips-for-raspberry-pi/ for a workaround.

Estimated Battery Runtimes

You don’t need to reduce power consumption before looking at alternative power sources for your Raspberry Pi, but if you decide to use a battery, the combination of larger battery size (measured in mAh) and reduced power drain provides longer runtime.

What level of runtime can you expect? The Spell Foundry Raspberry Pi Battery Life Calculator web site ( http://spellfoundry.com/raspberry-pi-battery-runtime-calculator/ ) provides typical estimated runtimes for standard RPi models in different configurations:

• Selected Pi model

• Pi with USB Wi-Fi adapter

• Pi with Pi Camera

• Pi with USB Wi-Fi adapter and Pi Camera

You might be surprised to discover that using the standard 5MP or 8MP Raspberry Pi camera has a much larger impact on battery life than using a USB Wi-Fi adapter. Figure 10-4 illustrates estimated runtimes based on a standard 2000mAh battery for four current Raspberry Pi models:

• Pi Zero

• Pi A+

• Pi 2

• Pi 3

Figure 10-4. The single biggest impact on estimated runtime is using the Pi’s camera

Figure 10-5 illustrates estimated runtimes for the same models based on a 4000mAh battery.

Figure 10-5. Doubling the mAh (milliampere-hour) rating doubles the runtime

To increase battery life over these figures, use the tips provided in the section “Configuring the Raspberry Pi for Minimal Power Consumption ,” in this chapter.

MoPi Mobile Power for Raspberry Pi

The MoPi mobile power peripheral for Raspberry Pi connects to the first 26 pins of the 40-pin GPIO interface on newer models and also supports the early models that have a 26-pin GPIO interface. MoPi uses the I2C bus, the 5V out pin, and a ground pin. It offers the ability to connect to almost any type of power supply that can produce at least 6.2V DC under load (maximum is 20V DC).

Although it includes two default battery profiles (nonrechargeable or nonbattery; eight NiMH rechargeable batteries) that are jumper-selectable , MoPi includes a configuration utility that is used to select power supply type, number of individual battery cells, and battery chemistry.

The software used by MoPi includes

• simbamond : SIMple Battery MONitor daemon (system service)

• mopi : Configuration tool similar in appearance to raspi-config

• mopicli : Command-line interface (CLI) for mopi

• monit : Monitors simbamond and other system statuses

In addition to providing optimized power for the Pi, MoPi can shut down the Pi in a controlled manner before the battery source runs out of power, acts as a UPS when both battery and nonbattery power is available, supports hot-swapping of power supplies, and has an integrated on-off switch. MoPi supports programs in Python.

The current model does not support the Raspberry Pi 3 (but supports the Pi 2 and all other models). An updated version (tentatively named MoPi ++) will support the Pi 3 and is expected by the end of 2017.

To learn more about MoPi, see https://pi.gate.ac.uk/pages/mopi.html . To order MoPi, see https://pi.gate.ac.uk/pages/get-mopi.html .

LiFePO₄wered/Pi 3

The LiFePO₄wered/Pi 3 is optimized for extreme portability. Like the MoPi, it uses the I2C bus for communications. However, it uses only the first eight pins of the Pi’s header. It is compatible with all 40-pin GPIO Raspberry Pi models. A Pi Zero will need to have an eight-pin header installed. Minor adjustments are needed to run on Model A and Model B.

It includes a 1500mAh lithium iron phosphate (LiFePO) cell that has a nominal output voltage of 3.2V, a smart USB charge controller , autoadjusting for input amperages ranging from 1.33A to 500mA, MPPT (solar cell) compatibility, power management, auto shutdown when battery voltage approaches critical levels, a wake timer, auto boot when sufficient power is restored, and charge and power LEDs.

LiFePO₄wered/Pi 3 uses a CLI (command-line interface) tool to change parameters. To learn more about the /Pi 3 and original /Pi versions or to purchase, go to http://lifepo4wered.com/ .

Sleepy Pi and Sleepy Pi 2

Sleepy Pi (26-pin Raspberry Pi) and Sleepy Pi 2 (40-pin Raspberry Pi) combines the microcontroller interfacing of an Arduino with a real-time clock and wake-on-demand circuitry, current monitor, and support for battery power ranging from 5.5-30V DC.

Like the other products we’ve examined, Sleepy Pi/Pi 2 connect via the I2C header pins. However, because Sleepy Pi products also contain the ATMEGA328P chip for Arduino functions, many additional pins are used (see Figure 10-6).

Figure 10-6. How the Sleepy Pi 2 routes signals between its built-in Arduino chip and the Raspberry Pi’s GPIO pins (adapted from a diagram at http://spellfoundry.com/product/sleepy-pi-2/ )

Both products are available in low-profile and stackable versions. The stackable version can be used with other add-on devices. For more information or to order in the EU , see http://spellfoundry.com/products/ . To order in the United States and Canada, visit http://buyapi.ca/ .