The timer should run while the circuit is powered by the battery then stop timing and retain the time required to drain the battery.

 

The timer is running off the battery you are draining?

Neat trick. I'd be interested in how to do it as well.

 

Doesn't need to be. The timer can be self-powered. However, it needs to shutdown and retain the cumulative time recorded when the circuit goes dead from a drained battery.

 

What is this for? A micro, couple dozen lines of code, voila!

 

Using for a science fair project - measure battery capacity for different battery types (not brands). Working to determine power-hrs for batteries when divided by cost will yield best bang for the buck.

 

A cheap USB Oscope.
Check the specs on them to find one with a graphic display that is time scaleable. This will show the length of usable power output and the time of decline from end of usable life to total exhaustion.

 

Will check into it.

 

Here is one with logging function that can be displayed via excel file.

http://digital-measure.com/html/usb_voltmeter.html

 

The device you're looking for is a common, 1.5V cell powered analogue quartz clock.

 

Sounds simple enough - but does not log the data, nor does it measure voltage decay. I found a device that does

 

Sounds simple enough - but does not log the data, nor does it measure voltage decay. I found a device that does

No it doesn't, but In none of your previous posts did you mention a requirement for data logging or voltage measurement.

 

Why measure and not log?

 

Why measure and not log?

If you have a bunch of different AA cells and you want to know which performs the best (for a particular load) you only need to do a comparative test i.e. apply the same load to each cell and measure how long it takes for the voltage to fall below some arbitrary threshold e.g. 1V or, less precisely, whatever voltage the clock stops working at.

But, again, this is exactly what you asked for:
"I need a timer for a dc circuit (aa battery) with a light bulb that exhausts the battery"...... "The timer should run while the circuit is powered by the battery then stop timing and retain the time required to drain the battery."

 

(ignore me i just think loud while you do your stuff) -- #9 is interesting if it can be integrated to required sys which we don't know yet what it'll be

about the battery draining requires 2xAA in series for std. *2.4V 3xAA for std.*3.6V incandescent to glow
however it does not need to glow having the cold filament resistance about 350mΩ or higher depending of type* (output power)
◄ forgot there are those
the AA battery is most likely performing best at about 24ohm series resistor discharge

▲ normally this or less capacity
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he shows the relevant number just at the beginning
it'd be thoughtful to use some device of common in the market
or then (exceeding the scope and likely the time you can spend on it !!!!!!!!!!!!!!!!!!!!!!) the opposite - some exotic stuff in comparison with ordinary
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• (out of scope of your prj.) the battery however **recovers if not fully drained and if not used for weeks/months to 50% of it's initial performance
  
• Energizers and some other alkaline-s tend to increase their power output (No-load terminal voltage) at the beginning of over moderate discharge likely due internal heating
• (out of scope of your prj.) it'd be interesting to know the No-load terminal voltage (and thus internal resistance) during discharge (levels)
  • only way is to measure this - for that you need - for a very small period (so the battery won't much recover)** - break the circuit - sample/log the No-load terminal voltage . . . continue discharge
  •• on this small smpling window the V.term will not be stable (the more correct is the lowest reading !!!) as you break circuit and connect voltage probe there's also some time to charge it's input capacitance to reach the valid lowest reading!!!

 

here some more of a setup
a clock not a timer (but theres quite in detail description of everithing and link to site that may have the bits of information required to make your presentation)

about display multiplexing http://thecustomgeek.com/2011/06/29/multiplexing-for-a-7-year-old/ (also the site may contain the ideas that could be adaptad to your needs)

what i actually searched and did not found was a simple MCU based LCD stopwatch with some PC logging interface (or on board "results" memory) - eighter with man or electronic reset/start stop/log(store) controls . . . ((not that day i guess))

what you actually require is any kind of stopwatch clock that you either manually or electronically start / stop and eigther manually or electronically log the results for (consider budget as time as money as what you know and what you need to learn)

while so - if the clock is digital - the display is likely necessary to be able to confirm the operation going on as required

setting up the LCD control yourself requires a lot of pre knowledge - thus there are modular LCD displays with input control - you just need find one that suits your needs and budget (you likely need the electronical stop and HOLD-display for stopwatch - by sudden battery voltage drop at near before it gets empty - the analog clock can be used if you master the el-mechanical actuator to do the trick)

 

actually we don't know your starting platform
if you generate you current (and voltage) sampler interrupt by a control PC or MCU
AND your system clock runs there you just need to setup extra timer there
or store the AA draining process start and stop times as sys timer counter values

if you already have an interrupt timer (other than the one in PC or MCU)
for measuring the current of the battery being drained

• the reasonable interval depends on draining speed for 200mA to 500mA the 30s sampling interval is fairly good while for say 1A it'd has to be 1s range

. . . so if you already have a sampler timer setup with the fixed interval
you just can count these intervals , multiply 'em by the duration of the single one . . . an you get your total time

• where the counter is stopped by battery terminal voltage dropping below say 0.5V or less (the smaller resistor for battery load the lower the STOP threshold voltage)
  
• or battery current dropping down to 60mA to 1mA depending what it is during the normal discharge time (the lower the current the lower the STOP current)

if you haven't came up with any concept yet - go consult with your class instructor (make notes . . .)

 

(i always run a post-error-checking - even when they've already unmounted what we once installed - e.g. - what is been learned since and by that what should've been done differently )

the major challange here is to measure the current correctly
if you plan to use the 1.2 to 1.5V AA and incandescent bulb:

• find/map/adjust your device/system for systematic error (assuming) I.BATT = amplified.scaled.ranged.MCU.A/Dinput(U) / R.fix.sense
  
• calibrate your bulb for I=functionOf()V.terminal -- enables to masure IU simultaneously (requires calibrating the calibrated set of "sampling lightbulbs") -- also may involve the µ-controllers A/D inputs systematic error²

since the unload graph is changing (dropping) fast near start(battery is fresh) and near the end (battery's becoming exhausted)
-- it'd be reasonable to tie the sampling rate to voltage change speed (faster change - more samples)
---- because too low sampling rates may alter the true capacity estimation and too high sampling rate (while it's not required at the middle of discharge cycle) generates you vast volumes of data that won't significantly effect the end result