Embedded Computing – Chuck Malloch

Category: Embedded Computing

Smarthome-type Candidate Networks

Posted on April 4, 2026April 16, 2026 by CBMalloch

Long-range off-the-grid communications
- Meshtastic
  - LoRa sub-GHz radio band, e.g. 915MHz in the US
  - mesh, broadcast, forwarding, max 7 hops
  - normal use case – short text messages
- MeshCore
  - LoRa sub-GHz radio band, e.g. 915MHz in the US
  - mesh, using path learning
  - AES encryption
  - devices have fixed roles: companion radio, repeater, room server, stand-alone device
- Reticulum
- LoRa and/or HAM
  - APRS – Automatic Packet Reporting System “Packet Radio”
    - Digipeaters
    - aprs.fi
Wireless Personal-Area Networks
- BSR X-10
  - power line transmission
- XBee
- Zigbee
  - 6LoWPAN/IEEE 802.15.4
  - 2.4GHz, sub-GHz, e.g. 915MHz radio bands
  - 10-100 meters, line-of-sight
  - star, tree, mesh
  - Zigbee coordinator (ZC), router (ZR), end device (ZED)
  - encryption
  - optimized for battery-operated devices
  - network layer, application layer, Zigbee device objects (ZDO), manufacturer-specified application objects
- Z-Wave
  - sub-GHz radio band, e.g. 915MHz in the US
- painlessMesh
- Thread
  - 6LoWPAN/IEEE 802.15.4
  - 2.4GHz radio band
  - can be run on ESP32, perhaps on ESP8266
  - IP-addressable
  - cloud access
  - AES encryption
  - optimized for low-power and battery-operated devices
  - open-source implementation OpenThread via Google
    - OpenThread network simulator
- Tasmota
  - Protocol for ESP devices
  - Supports Matter, but only (so far) over WiFi
- Matter
  - Lives atop Thread; can also live atop WiFi

Chuck’s SDP Links

Posted on April 4, 2026April 4, 2026 by CBMalloch

Articles especially pertinent to Senior Design Projects

“In theory, there’s no difference between theory and practice. In practice, however…”

Please share the problems you encounter! Participation builds a stronger community.

A must-watch video: Mistakes to avoid when designing a PCB I have seen most of these bite SDP teams where it hurts…

More board design points: ESD Protection for Your Board

Design Patterns — Useful schematics in KiCad — Really excellent presentation about making your schematics readable!

More design patterns, this time from TI

And yet more copy-paste sub-circuits culled from Github

Long-term waterproofing for submerged projects (much more at the Cave Perl Project)

Detecting hidden cameras post from Hackaday

And more on detecting hidden electronic devices

Designing circuitry for BLDC motor control, including ADCs, FET choice, gate drivers, and big high-current motors in industrial robots

U.Illinois Robotic Systems book – work in progress. In particular, this book already has nice sections on forward and reverse kinematics.

Switching Mains Power – not fully investigated yet. A place to start your investigation.

Sonoff S31 Mains Power Switches

Sonoff S40 Mains Power Switches

Adafruit Power Relay Module

Surface-mount soldering tutorial

Soldering the Tektronix Way – Training Videos

“Ideal Diodes”: Protect Your Project from Reversed Polarity Power

Overcoming the parasitic capacitance of a photodiode

Decoupling Capacitors – 0.1µF is suboptimal

Don’t use Nyquist as your only criterion for choosing a sampling rate

RP2040 resources from Cornell from their microprocessor design course ECE 4760

Wearable sensor for continuous analysis of sweat

Astrophotography and the new HD Raspberry Pi Camera

Raspberry Pi HD Camera for astrophotography

AstroPitography | Dr Adam Luke Baskerville

My DIY 8″ Telescope & Raspberry Pi HQ Camera

Astrophotography with Raspberry Pi HQ Camera and Celestron Astromaster 130 EQ

New Pi camera – any good for Astrophotography?

I2CWrapper – Using microcontrollers to translate I2C for non-I2C devices

System for digital signing of photographs

… and breaking the system for digital signing of photographs

Forest-deployed wildfire sensing and reporting system

New series of ATtiny µP eliminates requirement for dedicated pins

And also for JDP

Some insight into the design process for audio pedals (note: using STM32!)

Blogs and Vlogs

Engineering, specifically EE, CompE

Eric Bogatin – Practical EE/CompE fundamentals and practical skills

Andreas Spiess – LoRa, low-power, sensor networks, ESP8266, ESP32

Jay Bowles – The Plasma Channel – Plasma physics experiments (usually involving high voltage)

e.g. Using High Voltage to Obtain Water from Coastal Fog in the Desert

David Jones – EEVblog; instrumentation, troubleshooting, repair

Bil Herd – electrical engineer, designer at Commodore; CPLD, PLL

Moritz Klein – Audio electronics

Fran Blanche – FranLab; Apollo flight computer, DSKY, FranTone audio pedals

Big Clive – tear-downs

Ben Krasnow – Applied Science; including electronics; how he built his own electron microscope

Alan [w2aew] – tutorials on components; ham radio; RF

Security

Steve Gibson – Security Now podcast – a MUST for computer security folks; good episodes on internet components

Science & Math

Michael Stevens – Vsauce, The Mind Field

Grant Sanderson – 3Blue1Brown; math concepts, including a good visualization of Fourier analysis

Ben Sparks, Holly Krieger – Numberphile; math concepts, including large numbers and number theory

Matt Parker – Stand-Up Maths, lectures at Royal Institution

Brady Heywood – Understanding Complexity, complexity theory

Grady Hillhouse – Practical Engineering, particularly civil engineering

Steve Mould – Science vlogs, how things work

Collin Cunningham – “Lab Notes”, quick videos about electrical components and Adafruit products

Making, Robots, and Machinery

Adam Savage – amazing maker, MythBusters

Simone Giertz – general making, silly projects

Jeremy Fielding – general EE topics; built a cool robot arm

Tim Hunkin – very fun arcade game maker – machining tips

Internet Black Hole – Danger!

Destin Sandlin – SmarterEveryDay; how stuff works, including helicopters, nuclear subs, the James Webb space telescope

Derek Muller (PhD Physics) – Veritasium

Mark Rober – e.g. squirrel obstacle course, glitter bomb, world’s smallest Nerf gun

Markus Voelter – Omega Tau podcast; aviation, gliders, rides in fighters. Half of his podcasts are in English; the other half in German. Sadly, not being updated since a few years ago…

Scary (but interesting) stuff – Don’t do this at home (nor at M5, nor for SDP)!!!

Mehdi Sadaghdar – ElectroBOOM; high-voltage stuff; fun to watch

Colin Furze – crazy powerful builds

Plasma Channel – plasma thrusters, very high voltage projects

Styro Pyro – big scary lasers

Erratum – Arduino external forced reset circuit

Posted on January 6, 2021January 6, 2021 by CBMalloch

My previous post (Watchdog watchdog) sought to fix a problem – the Arduino ATmega328 I was using to monitor my heating system would occasionally hang. It would remain hung despite the use of the built-in watchdog timer to reset it. I’m not sure why, but I suspect it’s related to the electrical environment. In particular, I’ve replaced the entire Arduino board, and tested the program on the bench (where it worked perfectly, resetting as intended). I tried reconfiguring the watchdog interrupt service routine to pull Arduino pin 12 low and connected that to the ~RESET line. Still no good.

Fast forward (a few years!) while I ignore the problem and manually reset the Arduino every couple days. Finally, I designed and built a new circuit to power-cycle the Arduino; it worked perfectly on the bench. But not in deployment. Rats!

So I did a little modification – I removed the MOSFET and other power-cycling components, and dedicated a pin of the ATtiny to the inverse of the power-cycling pin – it is pulled low when a reset was needed. That pin is connected to the ~RESET line on the Arduino board. It looks like this works. I’ll update this post with news, and if it looks good, with the new program and circuit documentation.

Watchdog watchdog

Posted on December 30, 2020January 1, 2021 by CBMalloch

Well. It’s been a while. Here’s what’s new:

I monitor my heating system (temperatures, zone activation) with an Arduino, and relay the values to my home monitoring system through an ESP-01 / ESP8266. The Arduino occasionally hangs up.

I have tried to fix this by checking the power supply for good clean power; by making it reboot itself every 24 hours; by enabling the ATmega328’s watchdog timer. It still hangs up.

When it is running, it flashes an LED connected to the standard pin 13 of the Arduino. I recalled seeing that a 555 timer could be used as a missing-pulse detector. This would trigger if the 1Hz flashing stops. Cool. The missing pulse detector takes its output low during pulse starvation, and takes it high during the happy times when the pulses continue. I needed to take that prolonged low value and turn it into a one-shot pulse to drop and resume the power to the Arduino, and a second 555 could be configured as a one-shot to create this pulse. I had to add a capacitor in between to prevent continuous retriggering of the second 555, which would keep the power off to the Arduino.

The circuit “1” in the schematic illustrates this setup.

I happened to have a 556 handy, which comprises the functionality of two 555 timers. The equivalent simpler circuit is “2” in the schematic.

But, duh. I’m really more of a programmer at heart. And I had some ATtiny85 chips around. So I created an Arduino program to embody all the above functionality in a much simpler circuit – “3” in the schematic.

Note: in the code and the schematic the name ATmega refers to the (processor on the) Arduino board.

Watchdog_watchdog_sch

And I put it all onto a very small solderless breadboard. Since I needed regulated 5V to feed all the components, I put standard voltage regulation onto the breadboard as well.

The Arduino program was very simple:


/*
  Watchdog_watchdog
  
  One of my Arduinos, the one that monitors temperatures and zone activations 
  in my heating system, occasionally hangs up. This despite the fact that I'm
  using the ATmega watchdog to automatically reset it if it hangs. Dunno why. 
  The power seems good and stable. I've tried replacing the ATmega chip.

  I've decided to kill a flea with a cannon. The ATmega blinks an LED at 1Hz
  to indicate that it's still alive - I call this a throbber. The ATtiny will 
  monitor the throbber and if it stops, it will power-cycle the ATmega.
  Hah.

  The MOSFET in question will be a p-channel MOSFET configured on the high side
  of the power to the ATmega; when its gate is pulled low, it allows power to 
  flow to the ATmega. The specific MOSFET I'm using is a 5LP01SP, which is a 
  p-channel device whose pins are 1=source, 2=drain, 3=gate.
  
*/

#define pdThrobber_in 3
#define pdMOSFET      4

const unsigned long resetAfter_ms = 2000UL;
unsigned long lastThrobAt_ms = 0UL;


void setup() {
  pinMode ( pdThrobber_in, INPUT );
  pinMode ( pdMOSFET, OUTPUT );
}

void loop() {
  static int throbberStatePrevious = 0;
  int throbberState = digitalRead ( pdThrobber_in );
  if ( throbberState != throbberStatePrevious ) {
    lastThrobAt_ms = millis();
    throbberStatePrevious = throbberState;
  }
  if ( ( millis() - lastThrobAt_ms ) > resetAfter_ms ) {
    // BOOM. Cause a reset
    digitalWrite ( pdMOSFET, 1 );  // turns off ATmega
    delay ( 500 );
    digitalWrite ( pdMOSFET, 0 );
    delay ( 5000 );  // time enough to let the ATmega boot up
    lastThrobAt_ms = millis();  // reset the watchdog
  }
}

ATtiny Development Board

Posted on March 21, 2019August 25, 2020 by CBMalloch

I recently had to program an ATtiny85. As I was developing, I got tired of repeatedly wiring the connections between a 6-pin ISP socket and the ATtiny, and wanted something more permanent. I found myself sucked into Eagle CAD and this is the result. It has everything necessary to program 8-pin and 14-pin Atmel microcontrollers ATtiny25, ATtiny45, and ATtiny85.

[Read More...]

Experiment with CircuitPython, Jupyter, and WordPress

Posted on August 11, 2018August 25, 2020 by CBMalloch

I’m trying to embed a Jupyter notebook page as a blog post. I saved it as html, and copied an pasted that html below. I don’t think that’s the best way to do it.

We are exploring the Adafruit Metro M4 Express

[Read More...]

Chuck Malloch

Audio and Home Control Electronics

Category: Embedded Computing

Smarthome-type Candidate Networks

Long-range off-the-grid communications

Meshtastic

MeshCore

Wireless Personal-Area Networks

BSR X-10

XBee

Zigbee

Z-Wave

painlessMesh

Thread

Tasmota

Matter