Phoebe guidesA field team faces an unresolved physical question: When the LDR divider stops being negligible They must answer it before changing ldr divider duty cycle on the real device. Predict the direction first.
See the relationship before changing it
The figure reads from left to right. The blue card is ldr divider duty cycle. The middle card applies this page's relationship. The green card is total daily charge. Walk the arrows once: set the input, apply the rule, then read the result with its unit.
The retained audit below checks several chapter fixtures. This added model holds every other chapter fixture fixed, so the numeric fixture does not switch without explanation.
Derive the baseline in four named moves
- 1
Name the input. The chapter baseline for ldr divider duty cycle is 100.
- 2
Name the relationship. Qsensor=Ibrightx24hxd; Qtotal=Qmotor+Qsleep+Qsensor; life=C/Qtotal
- 3
Substitute the chapter fixture. Set ldr divider duty cycle to 100. The page ledger gives total daily charge as 31.220 mAh/day.
- 4
Read the result. Keep mAh/day beside the value. Use it only inside the technical boundary on this page.
Predict, then change ldr divider duty cycle
Try Predict the direction of total daily charge. Move one control, calculate, then check your prediction.
Observe The widget multiplies the same 0.320 mA by biased time, adds the chapter's motor and sleep terms, then divides capacity by daily charge. Reset the control to 100 and compare total daily charge.
Explain Only ldr divider duty cycle moves here. The other chapter fixtures remain fixed.
Check yourself
What should you do before trusting a moved-control result?
What does this small model leave out?
1. A divider draws current whenever biased
The LDR and fixed resistor form one path from 3.3 V to ground. At the chapter's bright point, that path draws 0.320 mA whether or not firmware is using the ADC result.
2. Convert current into daily charge
Continuous biasQsensor=Idiv×24 h.
Duty-cycled biasQsensor=Idiv×24 h×duty fraction.
Total budgetQday=Qmotor+Qsleep+Qsensor.
3. Turn daily charge into days
The units cancel: mAh divided by mAh/day leaves days. This is an arithmetic estimate, before battery aging, converter loss, and discharge-rate effects.
4. Try the divider duty cycle
TryMove from a 0.1% sample pulse toward an always-on divider.
ObserveAlways on, the divider adds 7.680 mAh/day, raises the total to 31.220 mAh/day, and gives about 80.1 days.
ExplainThe widget multiplies the same 0.320 mA by biased time, adds the chapter's motor and sleep terms, then divides capacity by daily charge.
This uses the chapter's bright-case current as a conservative fixed value and ideal charge division.
- the light-dependent current distribution
- Needs separate evidence
- switch leakage
- Needs separate evidence
- settle time
- Needs separate evidence
- ADC acquisition
- Needs separate evidence
- motor duty/current spread
- Needs separate evidence
- regulator efficiency
- Needs separate evidence
- battery temperature/aging
- Needs separate evidence
- usable capacity
- Needs separate evidence
- low-voltage cutoff measured
- Needs separate evidence
Use field evidence or a deeper model before release.
5. Work the always-on case
Against the exact divider-off arithmetic baseline of 2,500/(23.3+0.24)=106.2 days, the always-on divider reduces life by 24.6%. The chapter's 25.1% figure instead uses its rounded 107-day baseline.
6. Work the sampled case
The chapter's 100 µs window at about ten reads per second is a 0.1% duty cycle.
That term is genuinely tiny beside the 23.3 mAh/day motor budget. The disagreement between “negligible” and “costly” is entirely the switching assumption.
7. Check yourself
How much charge does 0.320 mA use in 24 hours?
Why does 0.1% duty divide that result by 1,000?
Is 80.1 days a field guarantee?
These are the chapter inputs, worked results, and named teaching assumptions.
- 0.320 mA bright-divider current
- Current or responsivity value
- 23.3 mAh/day motor term
- Time, interval, or service-life value
- 0.24 mAh/day sleep term
- Time, interval, or service-life value
- 2,500 mAh capacity
- Charge or energy value
- 7.68
- Chapter input or worked result
- 31.2 mAh/day results
- Time, interval, or service-life value
- exact 106.2-day arithmetic baseline
- Time, interval, or service-life value
- about 107-day rounded chapter baseline
- Time, interval, or service-life value
- 80.1-day always-on result
- Time, interval, or service-life value
- 24.6% exact-baseline reduction
- Percentage, ratio, or gain
- 25.1% rounded-baseline reduction
- Percentage, ratio, or gain
- 100 µs at about ten reads per second
- Time, interval, or service-life value
- 0.1% duty
- Percentage, ratio, or gain
- 0.00768 mAh/day sampled result come from the chapter
- Time, interval, or service-life value
The arithmetic is not a battery qualification.