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@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. -
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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... ;-) -
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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?
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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 thepinMode()
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. -
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
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German IT developer who found his long lost love for electronics and connected devices...