From API to Electrons A journey on Tessel from JS to the metal…

…and back

Eric Kolker Technical Machine FIT 2014

Intro

◦ I’m Eric Kolker

◦ Electrical engineer, @technicalhumans

◦ Our adventure today:

What happens when you set a noise trigger

with Tessel and the Ambient module?

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Case study: the Ambient Module

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tessel run ambient.js

◦ JS transpiled to Lua via Colony

◦ Embeddable, low memory footprint,

semantically similar to JS

◦ Dependencies bundled

◦ Bundle stored in RAM, executed

◦ tessel push = saved in flash

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JS C

Lua

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Microphone

Light sensor (photodiode)

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Microphone

Light sensor (photodiode)

To SublimeText!

◦ Tour of ambient JS driver (index.js)

◦ Tour of ambient firmware (ambient-attx4.c)

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Firmware & driver recap

◦ Setup

◦ SPI communication

◦ Interrupt-driven

◦ ADC read

◦ Threshold detect

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To the schematic!

◦ Ambient schematic

◦ All our design docs

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Functional blocks

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(Approximate) system block diagram

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Signal ADC 1/s

To SPICE!

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Simulation results: time domain

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Simulation results: frequency domain

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Simulation results: frequency domain

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a = 0.9

a = 0.5

a = 0.3

Welcome to the bottom

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Time to head back to JS!

(This direction is a lot faster)

Simulation results: time domain

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Simulation results: time domain

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Everyone’s take on the situation

◦ Analog vs. digital

◦ Binning

◦ Sampling

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Triggered!

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Back to the firmware, JS

◦ ADC compare, module sets IRQ high

◦ Tessel handles SPI, saves data payload

◦ Callback pushed to top of queue

◦ Callback evaluated with given data

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Recap

◦ User code

◦ JS binds to Lua, Lua VM in C binds to HW

◦ Communication over SPI

◦ Interrupt-driven ADC reads, compares

◦ Yay, op amps for signal processing! SPICE!

◦ Data sent to Tessel, event fires, callback runs 38

Thanks!

Questions?

e@technical.io

@twiddlee

ekolker

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APPENDICES

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Resources

https://github.com/ekolker/fit-2014

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