Category: Firmware Development

Watchdog watchdog

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

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.

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Updating some, but not all, old technology

Lightning strikes. It struck near me, and fried a component of my old X10 home-control system.

X10 is a power-line-based communications network. Data is sent (slowly) over the house power lines by injecting a 120 kHz signal into the 60 Hz AC signal just after the zero-crossing of that signal. One bit per cycle is sent by either adding or withholding a short pulse of the 120 kHz.

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Experiment with CircuitPython, Jupyter, and WordPress

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

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Thoughts on serial communications

Maybe these issues have been solved in the past. I don’t think there is necessarily a very good solution, though.

The problem is that serial communications is imperfect. Characters get messed up in transit between two devices. When they do, that in turn messes up carefully thought out protocols, like “Capture characters in a buffer until you see the linend; then process the buffer as a single message.”

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Teensy, touch sensing, and ESP8266 – via MQTT and Raspberry Pi

Whee!

I have a demo/development setup on a small breadboard which powers an ESP-01 ( the small, cheap, 8-pin breakout board for an ESP8266 chip ). In addition to being a programming board, it has 3v3 voltage regulation, a pot, a temperature sensor, a simple LED, and a WS2812 3-color LED. I have the installed ESP8266 running a program to subscribe to an MQTT broker and light the LEDs according to publications on a certain topic.

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Securing a Raspberry Pi IoT Gateway

I believe that the UMass IT policy forbids “rogue” WiFi gateways in order to prevent anonymous Internet access, so that nefarious actors can be identified.

I needed to create an IoT server for my lab, M5, and it needed to be accessible via WiFi. It also needed to have Internet access so that I could keep its Linux firmware up to date.

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The overloading of potentiometers

Creating complex firmware for existing hardware is often complicated by unforseen ( or ignored by the hardware designer ) human-interface issues. One example of this situation comes up when a project requires more settings than there are physical controls for. Modern cameras provide examples of the problem, and also of its solution.

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