How to measure current consumed over time?

[n_grimm]

Hello friends. I have one of the audio players/recorders from Radio Shack similar to those used in greeting cards. I measured about 11 ma during play. I am powering it with (4) rechargeable 2500 mah lithium AA cells in series to achieve 9 volts so that comes to 227 hours if played continuously. The problem is that I am activating the playback about once per second for a short sound effect and I don't know what the duty cycle is. I could guess and say 50% etc. but I am trying to figure out a way to get an actual current measurement for a fixed period of time like a minute or hour etc. Forgive me if I'm overlooking something simple. Thank you.

 

[MikeMl]

You have to integrate the current over time. Not easy unless you have a data acquisition system, and some software. I could do it with a small USB two channel data recorder, which lets me make a comma separated file of current vs time. I would then read the waveform into EXCEL, and do the integration and plotting there.

 

[crutschow]

If the current draw is fairly constant, then you just need to measure the on-time of the playback. You perhaps could use the activating signal or sense the current flow with a small series resistor to control a time or stop-watch counter circuit. At the end of the measuring period just multiply the total time count times the current draw to get the total mAh used.

Edit: There is stopwatch function software available for a PC that can be externally controlled from the COM port (such as this) that would measure the time .

 

[BrownOut]

I think all he wants to do is measure the total play time over a specified time period ( hour or minute ) In that case, just connect a time counter and let the dang thing run for whatever time period you want to use, then observe the time run off on the timer. A suitable time counter may be purchased, but if you want help making one, I'm sure that help is available here, also I'm sure many timer schematics are available on the web.

 

[OldTechie]

If the current draw is constant while the recorder is playing, then you can just measure the amount of time the recorder is playing, then calculate the duty cycle. DutyCycle = PlayTime / TotalTime. (Use hours for the time calculation). BatteryVoltage * DutyCycle * Current (in MA) = MA-Hours from the battery.