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Fatherof2

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  1. Thanks all for the suggestions. I may use the Stop Watch method, as suggested, for awhile to get get things started. Meanwhile looking for a more automated way to time it. The stop watch idea is good and basic, but poses potential problems like forgetting to check it before the cells run out of juice...then you don't know when it stopped. And we have about 8 different cells to test. But better to get on with it than to hold things up while Dad is trying to do something fancy, eh? ;) ;)
  2. Thankyou so much for the quick reply. To answer your question 7th gd. is middle school; age for 7th graders is 12-13y.o., 8th gd is 14-15, etc. Your solution is a bit much for this 12 year olds science project. I was looking for something much simpler. Plus she needs to monitor the test and note the findings in her notebook. Thank you anyway.
  3. HELP for a 7th gd science project. HYPOTHESIS: do disposable AA cells last longer than rechargeable cells in a portable CD player? SET-UP: 2 AA cellS driving CD player. In series with cd PLAYER is an ampmeter; a DVM measures cell voltage. Added a digital clock to stop when the batteries discharge enough to stop the CD Player. THE PROBLEM: the CD player stops playing within an hour but the clock still ticks. The clock uses only 1 AA cell whereas the CD uses 2. The clock uses only .16mA and the CD starts at 300mA then drops to 120mA after 30 sec. Tried, among other configurations, to add 0.5 ohm resistor in series with CD player to drive the clock but this produces an IR drop of only 0.6V or so, not enough to drive the clock. QUESTION: is there a timer with a sensing input that I can buy, or build, that I can connect to this lab set-up in order to sense when the CD player stops running? It could be connected to sense the current because the current drops to zero when the CD player shuts off. Would an inductor in series with CD player be the appropriate component to produce a pulse? PLEASE HELP, DEADLINE IS LATE JANUARY.
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