Around the World in 80 MicroAmps - Battery tech for IoT

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.header[.floatleft[.teal[Christopher Biggs] — Around the world in 80uA].floatright[.teal[@unixbigot] .logo[@accelerando_au]]] .footer[.floatleft[The Linux Of Things .hashtag.teal[lca2019] --- Jan 2019 Christchurch, NZ]]

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.header[.floatleft[.teal[Christopher Biggs] — Around the world in 80uA].floatright[.teal[@unixbigot] .logo[@accelerando_au]]] .footer[.floatleft[The Linux Of Things .hashtag.teal[lca2019] --- Jan 2019 Christchurch, NZ]]

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.header[.floatleft[.teal[Christopher Biggs] — Around the world in 80uA].floatright[.teal[@unixbigot] .logo[@accelerando_au]]] .footer[.floatleft[The Linux Of Things .hashtag[lca2019] --- Jan 2019 Christchurch, NZ]]

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.fig100[
![](lca2019-slide-template.svg)]

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.crumb[
# Intro
]

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class: vtight

# Who am I?
## Christopher Biggs — .teal[@unixbigot] —  .logo[@accelerando_au]

* Brisbane, Australia
* Linux user since the very beginning (floppy discs at 2400 baud!)
* Convenor, Brisbane Internet Of Things Meetup
* Founder, .logo[Accelerando Consulting]
* Accelerando is a "full service" consultancy - chips to cloud

???

I operate Accelerando Consulting which helps businesses
use technology to reduce stress.   Really, that's what
I believe, that technology is the gradual process of freeing
humanity from drudgery and fear, and I started Accelerando
because I wanted to contribute to a future that I will
be excited to live in.

---

# Shameless Self-Promotion

## Brisbane (AU) Internet of Things Meetup

* Evening Symposia 4th Mondays 
 * Afternoon Workshops 2nd Saturdays
 * Visitors and speakers welcome!

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.crumb[
# Intro
# Promise
]

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# The Promise

---

# Kill the clipboard

## Sensors everywhere*

.footnote[Hold the creepy]

--
## Control everything

--
## Reduced cognitive load => Bliss

---
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template: callout
.crumb[
# Intro
# Promise
# Problem
]

---
class: center, middle
template: inverse

# The Problem

---

# Wires are hard

---

# But use 'em if you got 'em

## PoE, EoP, EoC...

---

# Radio killed the Ethernet Star

## Wifi solves all our problems, right?

### Sure, for the first hour.

---

layout: true
template: callout
.crumb[
# Welcome
# Promise
# Problem
# Batteries 101
]

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# Batteries 101

---

# Batteries are pretty bad

---

# Battery tech

* Lead-Acid (cars, old solar)
--

* Nickel Metal-Hydride (satellites, cameras)
--

* Single-use Dry Cells - Carbon-Zinc, Alkaline-Manganese (dead cameras)
--

* Lithium (everything from phones, to cars, to grid storage)

---

# Thinking about Battery Capacity

---

# Lets build a FarmBot sprinkler
--

## Water tank <==>  Battery

## Water molecules <==> Electrons

## Hoses <==> Wires
---

# Lets build a FarmBot sprinkler

## Height of tank (water pressure) <==> Potential Difference
### Joules per Coulomb aka "Volts"

---

# Lets build a FarmBot sprinkler

## Amount of water flowing <==> Electric Current
### Coulombs per Second aka "Amperes"

---
# Lets build a FarmBot sprinkler

## Tank capacity (litres) <==> Battery capacity

### Number of electrons, aka Coulombs, or, more usefully "Ampere-Hours"

---

![](chapstick.jpg)

# Our standard battery

## One "Penguin Chapstick"
### (1PC == 2000 MilliAmpere-Hours == 2.0Ah)

---

# Lets ignore voltage, too, today.

* One Lithium-Ion Cell is 3.7 Volts*
* Most of our IoT electronics wants 3.3 Volts
* USB's 5 Volts makes a handy charging voltage

.footnote[ish.  Varies ~4.1V full, down to ~3.0v empty]
---

![](lies.jpg)

# EVERYTHING IS A LIE

* eg, Marked 5000mAh (2.5PC).
--

* In reality, less than one PC.
---

## Lies are so prevalent they created a market

* Inexpensive USB power loggers

.fig50[
![](power-meter.jpg)]--

* or, make your own with a measurement module and your Pi Zero

---

# But The Emperor (Penguin) Is Not Wearing Any Clothes

## Energy capacity is customarily quoted for 20-hour discharge

### Leaky pipes mean there is not a linear relationship

---

# Thank you, Nerds

## Lithium battery improvements driven by:

* Phones
 * Quadcopters
 * Electric Vehicles

---

.fig70[
![Magic Smoke](smoke.gif)]

.spacedown[
# "Please do not recline your seat"]

---

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.crumb[
# Welcome
# Problem
# Metering
# Batteries 101
# COTS
]

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# Commerical Off-The-Shelf solutions

---

.fig50[
![](powerbanks.jpg)]

.spacedown[
# Overdrawn at the Power Bank]

---

![](protection.jpg)

.spacedown[
# The Powerhouse of the Cell]

---

.fig40[
![](bms.jpg)]

.spacedown[
# A "Battery Managment System"]

---

.fig40[
![](solar.jpg)]

# Here comes the Sun

---

.fig30[
![](pi-hat.jpg)]

.spacedown[
# Pi is irrational
]
---

.fig60[
![](lifepo4wered.jpg)]

.spacedown[
#LiFePO4wered

## Thoughtful design

### (Still only runs a few hours)]

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.crumb[
# Welcome
# Problem
# Metering
# Batteries 101
# COTS
# Sleep
]

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# Using sleep modes to reduce power usage

---

# Computers are fast, objects are slow

---

# Wake me when something interesting happens

## General shape of deep sleep

* Configure one or more "wake interrupts"
* Turn off as much of the chip as possible
* Halt (or run very slowly) until an interrupt occurs

---

# Arduino deep sleep

* Interrupt pins
* Serial communications
* Sleep consumption as low as 6 *micro* Amperes (38 years / PC)
* But watch out for the stock voltage regulator (eats 10mA)

---

![](8266.jpg)

# ESP 8266 sleep modes

* "Modem sleep" just turns off the radio when not needed
* Light sleep - cpu is "idling"
* Deep sleep - cpu is halted
* Wire the wake pin to the reset pin
* Can deepsleep for up to 71mins
* You can jury-rig a reset-on-some-event

---

# ESP 32 Sleep modes

* As for ESP8266 but deep-sleep is much more useful
* Wake on defined transmition of any (one) IO pin
* Wake on one-low or all-high on a number of IOpins
* Watch out for complicated numbering of IO pins
* Wake on touch sensor
* Wake on signal from ultra-low-power coprocessor

.fig30[
![](esp32.jpg)]

---

layout: true
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.crumb[
# Welcome
# Problem
# Metering
# Batteries 101
# COTS
# Sleep
# ULP
]

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# Using Ultra-Low-Power coprocessors

---

# The ESP Ultra-Low-Power coprocessor

* A slow, 4-register, 16-bit RISC processor
* RTC "slow memory" can be accessed by main core
* Load a program into slow memory and run it
* Configure the ULP wake up interval
* ULP can choose to go back to sleep, or wake the main cores
* Fairly usable from RTOS and Arduino.
* **Maybe** could be jury-rigged from Python, JS or Lua

---

# ULP example (Arduino Code)

.code[
```c++
void setup() {

esp_sleep_wakeup_cause_t cause = esp_sleep_get_wakeup_cause();

if (cause != ESP_SLEEP_WAKEUP_ULP) {
        Serial.printf("Not ULP wakeup (i.e. cold boot) initializing ULP\n");
        ulp_load_binary(0, ulp_main_bin_start, (ulp_main_bin_end - ulp_main_bin_start) / sizeof(uint32_t));

ulp_max_count = 100;
        ulp_set_wakeup_period(0, 10 * 10000);
    }
    else
    {
        Serial.printf("ULP wakeup, inspect the status\n");
        go_do_stuff();
    }
    esp_deep_sleep_start();

// NOTREACHED
}
```]

---

# ULP example ctd. (ULP Code)

.tinycode.fl[
```c++
  .bss
  .global max_count:
max_count:
  .long 0
counter:
  .long 0

.text
  .global entry
entry:
  /* Read counter, increment, save back to RAM */
  move r3, counter
  ld r0, r3, 0
  add r0, r0, 1
  st r0, r3, 0
```
]

.tinycode.fl[
```c++
  /* check for a change of state on some IO pin */
  /* get count in r1 (code elided) */

sub r2, r0, r1
  jump wake_up, eq

/* Put ULP back to sleep */
  .global exit
exit:
  halt

.global wake_up
wake_up:
  /* Wake up the SoC and stop ULP program */
  wake
  halt
```
]

---

layout: true
template: callout
.crumb[
# Welcome
# Problem
# Metering
# Batteries 101
# COTS
# Sleep
# ULP
# DIY
]

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# Designing your own low power device

---

# Aim for efficency

* Sleep as much as possible
* Use interrupts not polling where possible
* Reduce unnecessary words
* Reduce unnecessary words

---

# Avoid nasty surprises

* Simple resistor ladders leak power
* Linear regulators eat power
* Poor antennas cost watts
* Beware USB programming bridges that are always on

---

.fig60[
![](battery_level.png)]

.spacedown[# Monitor your battery level

## ...but without wasting it
]

---

.fig60[
![](charger.png)]

.fig60[
![](regulator.png)]

.spacedown[
# Recharge in place

## Inexpensive single-chip Lithium battery chargers abound
]

---

# Turn off unused modules

* Got a radio transmitter?   Switch it off when not in use
* Need to receive?  Work out how to do that on a schedule

---

# Turn off unused chip features

* Shut off bluetooth if you're not using it
* Run only as fast as you need to

---

# Not so flashy

## If you must use LED indicators:

* Use low duty cycles (eg 100ms on, 900ms off)
* Use low intensity (either in software or hardware)

---

# Don't go *too* far

.fig80[
![](reverse.jpg)]

---

layout: true
template: callout
.crumb[
# Welcome
# Problem
# Metering
# Batteries 101
# COTS
# Sleep
# ULP
# DIY
# Results
]

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template: inverse

# Case Study: 5 years between meals

## Maybe

---

![](waterwise-lashup.jpg)

# The problem: wireless utility metering retrofit

* Monitor a physical rotating dial
* Optical or magnetic sensing of rotations
* Count rotations, transmit total periodically
* Run in a cellar or meter box, forever

---

.fig50[
![](waterwise-3d.jpg)]

# The solution

* ESP-32 microcontroller
* Wifi for setup and maintenance
* LoRA for communication every 15 minutes
* ULP coprocessor monitor 4 sensors
* ULP wakes CPU after number of elapsed minutes and/or pulses

---

.fig50[
![](waterwise-prototypes.jpg)]

# How's it stack up

* 150mA when communicating over wifi
* 100mA when communicating over for LoRA
* 50mA when idle, with radio(s) on
* 40mA when idle (radio off)
* 80uA in deep sleep
* Average under 1mA => battery life 1-5 years

---

layout: true
template: callout
.crumb[
# Welcome
# Problem
# Metering
# Batteries 101
# COTS
# Sleep
# ULP
# DIY
# Results
# Coda
]

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.fig30[
![](keep-calm.jpg)
]

# Recap

.nolm.vtight[
* Wires are hard
* Measure and understand your power usage
* Batteries 101
* Off the shelf battery systems
* The basics of "Deep Sleep"
* The ESP32 Ultra-Low-Power Coprocessor
* Designing your own battery-friendly systems
* Projecting and monitoring your battery lifetime
]

---

# Resources, Questions

## Related talks - [http://christopher.biggs.id.au/#talks](http://christopher.biggs.id.au/#talks)

- Email: .blue[christopher @ biggs.id.au]
- Twitter: .blue[@unixbigot]
- BNE IoT Meetup: .blue[@iotbne]
- Accelerando Consulting - IoT, DevOps, Big Data - .blue[@accelerando_au] https://accelerando.com.au/