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improving the battery readings

This commit is contained in:
Jorj Bauer 2017-07-18 02:13:12 -04:00
parent f1d74c1644
commit 58c636b484
1 changed files with 22 additions and 11 deletions
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33
teensy/teensy.ino
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@ -75,7 +75,7 @@ void setup()
pinMode(RESETPIN, INPUT);
digitalWrite(RESETPIN, HIGH);
analogReference(EXTERNAL); // 3.3v external, instead of 1.7v internal
analogReference(EXTERNAL); // 3.3v external, or 1.2v internal. We need 1.2 internal for the battery level, which means we're gonna have to do something about the paddles :/
analogReadRes(8); // We only need 8 bits of resolution (0-255) for battery & paddles
analogReadAveraging(4); // ?? dunno if we need this or not.
analogWriteResolution(12);
@ -263,26 +263,37 @@ void loop()
// FIXME: what about rollover?
nextBattCheck = millis() + 3 * 1000; // check every 30 seconds
// This is a bit disruptive - but the external 3.3v will drop along with the battery level, so we should use the more stable (I hope) internal 1.2v.
// The alternative is to build a more stable buck/boost regulator for reference...
analogReference(INTERNAL);
batteryLevel = analogRead(BATTERYPIN);
analogReference(EXTERNAL);
/* 204 looks like the top end (5.05v * (204/255), within tolerance of my resistors).
* Which suggests 176 is about 3.5v, which is the bottom 20% of discharge for LiIon.
* We'll call that 0% battery remaining to protect the battery.
/* LiIon charge to a max of 4.2v; and we should not let them discharge below about 3.5v.
* With a resistor voltage divider of Z1=39k, Z2=10k we're looking at roughly 20.4% of
* those values: (10/49) * 4.2 = 0.857v, and (10/49) * 3.5 = 0.714v. Since the external
* voltage reference flags as the battery drops, we can't use that as an absolute
* reference. So using the INTERNAL 1.1v reference, that should give us a reasonable
* range, in theory; the math shows the internal reference to be about 1.27v (assuming
* the resistors are indeed 39k and 10k, which is almost certainly also wrong). But
* then the high end would be 172, and the low end is about 142, which matches my
* actual readings here very well.
*
* Notes: 191/192 is 3.7v
* ... but 193/192 is also 3.57v. :/
* Actual measurements:
* 3.46v = 144 - 146
* 4.21v = 172
*/
#if 1
Serial.print("battery: ");
Serial.println(batteryLevel);
#endif
if (batteryLevel < 176)
batteryLevel = 176;
if (batteryLevel > 204)
batteryLevel = 204;
if (batteryLevel < 146)
batteryLevel = 146;
if (batteryLevel > 172)
batteryLevel = 172;
batteryLevel = map(batteryLevel, 176, 204, 0, 100);
batteryLevel = map(batteryLevel, 146, 172, 0, 100);
g_display->drawBatteryStatus(batteryLevel);
}
}