ChristianW

Most recent activity

• banglejs.com - hackable smart watch?!?

  @ChristianW started

  • 59 comments
  • 2,294 views

  @Gordon replied
• Detecting power loss (here: Pixl.js)

  @ChristianW started

  • 13 comments
  • 394 views

  @Gordon replied
• Detecting power loss (here: Pixl.js)

  in Electronics • 3 weeks, 4 days

  

  @allObjects thanks for the clarification.
  Actually it's not for a motorized vehicle but for a velomobile - a fully faired three wheeled recumbent. Because there is no dynamo you need a battery to power lights, indicators and horn.
  And if that goes down on longer trips you are busted, so I'd like to know how much is left and how much I currently draw.
  Because it is easy to do I'd also like to measure speed, cadence and distance - and store them in an EEPROM (see other thread). And the best time to store is when the battery is pulled.

• Detecting power loss (here: Pixl.js)

  in Electronics • 3 weeks, 5 days

  

  Thanks for the suggestion, I'll change the resistor setup tomorrow to be on the safer side.
  No voltages above 12,6 V (LiPo 3S) - and no charging while in circuit possible.
  So that should simplify things a bit...

• Detecting power loss (here: Pixl.js)

  in Electronics • 3 weeks, 5 days

  

  Not quite.
  The 12V pulls the pin high, but the (external) diode shortens that to 3,3V.
  I just measured the voltage to be about 3.8V on the pin.
  Do you think this is still an issue?

  For pulldown (in case of power loss) I used the internal resistor via pinMode()

  As with the flickering this may have been cause by wrongly wired MOSFETs or a shortage between 3,3V and 5V PIN.
  Prototyping got a bit messy lately... ;-)

• Detecting power loss (here: Pixl.js)

  in Electronics • 3 weeks, 5 days

  

  PS: Without BLE connection and LED off it is even 9 seconds feedback on the LCD!

• Detecting power loss (here: Pixl.js)

  in Electronics • 3 weeks, 5 days

  

  I just wired it up.
  Used a 10k resistor to pull D7 against Vin (about 12,5 V from my fully charged LiPo).
  Capacitor is a 1000uF / 25V.

  Strange thing: The display flickers and blacks out rhythmically while D7 is not configured.

  I used this script to test powerdown detection:

  function onInit() {
  
    pinMode( D7, "input_pulldown" );
  
    setWatch(function(e) {
      //LED.set();
      console.log( "power out" );
      var t=0;
      setInterval(function() {
        console.log( "t=", t++ );
      }, 1000 );
    }, D7, { edge: "falling"});
  }
  

  It gives me about 6 seconds console feedback before dying with the LED off:

  power out
  t= 0
  t= 1
  t= 2
  t= 3
  t= 4
  t= 5
  t= 6
  

  With LED set immediately after power down it is only two seconds (still enough for some cleanup probably).

  So basically it seems to work.

  @Gordon: is it normal that it behaves strange when certain pins are used as inputs bot not configured yet?

• Detecting power loss (here: Pixl.js)

  in Electronics • 3 weeks, 5 days

  

  Thanks, @AkosLukacs.

  I was considering the CR2032 backup, but was scared to mess with two inputs.
  Thanks for sorting that our.

  Actually it would be enough to have some cycles left for a EEPROM write, so a powercap or elko could just do.
  What about another pulldown between Din and GND?
  EDIT: I just found input_pulldown in the pinMode() documentation. That would do the trick, wouldn't it?

  It would be nice to use a setWatch() instead of polling external hardware.
  Maybe I'll give t a try later...

  The NRF52LL reference looks interesting, too. Did not know about it.
  Thanks.

• Detecting power loss (here: Pixl.js)

  in Electronics • 3 weeks, 5 days

  

  I am using a Pixl.js for a bike (velomobile) computer project.
  It should monitor the onboard LiPo battery with 11.1 V and is also driven by it.

  In case off immediate power loss (battery is dying or just disconnected) there should be a triggered routine to save some current data to flash.

  I was considering this:
  Battery power is monitored by an INA226.
  So one way is to regularly poll and detect an undervoltage.
  But this is slow and could only work for a slowly dying battery - no sudden disconnect.

  So another idea is this:
  Put a capacitor parallel to the Vin Pins to gain some time after power loss.
  Put a diode in front so the capacitor only feeds the Pixl, nothing outside.
  Wire the feeding current (before the doide) with a resistor (~10k) to a digital input.
  Put another small diode between 3,3 V and the input so the voltage will not rise above 3,3 V. (Maybe a Z-diode of about 3,3 V between GND and the input would be better?)
  As soon as the outside voltage drops, the pin will change to low and trigger a watch set on that pin.

  Will that work?
  Anyone tried something similar or has a better idea?

  Some ASCII Art sketch for clarification:

  Din  O---+--[R]----+
           |         |
           V diode   |
           -         |
           |         |
  3v3  O---+         |
              diode  |
  Vin  O---+---|<----+-------------O 
          +|                       + LiPo
          === capacitor
           |                       - LiPo
  GND  O---+-----------------------O
  

• Spare display for Pixl.js?

  @ChristianW started

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  @ChristianW replied