74hc4067 Multiplexer for multi-cell battery tester
hello,
i'm newbie arduino , electronics. i have arduino uno ethernet shield , have managed build circuit on breadboard uses 74hc4067 multiplexer open port , read input temperature sensor. it displays temperature reading on serial monitor. in sketch figured out how use web display same information. i mention give idea of skill level. the math of ohm's law makes sense me applying design of own circuits remains daunting.
so here's goal. i've built electric bike. it's being powered 72 battery cells scavenged old laptops. from reading on using these cells important match cells of equal capacity (measured in mah). difficult task used batteries. the best way charge cell , discharge it, measuring voltage drop on time calculate true capacity.
to can put large resistor on cell draw current , measure voltage drop. track on time , have need. simple enough (easy me say) single cell. but have 300 cells test. one cell @ time take forever using method.
so i'd build multi-cell discharger using 74hc4067 multiplexer read 8 or 16 inputs @ time. conceivably connect 2 multiplexers same arduino or build. multiple units test batteries in large batches. hopefully see i'm going.
the lithium ion battery i'm testing charged @ start around 4.0v (maybe 4.2v). the test draw down 3.0v, lets say. a test pull 1a , measure how long takes drop voltage (and calculate mah of cell).
here's problem. the 74hc4067 inputs supposed @ 25ma or less. if hook multiplexer across ends of resistor, won't current fry it? how measure voltage @ low current (25ma) compared drain of battery is?
somehow think if understood ohm's law better figure out i'm stumped.
if you've read entire post, patience. any tips or pointers appreciated.
p.s. have hall effect sensor?
i'm newbie arduino , electronics. i have arduino uno ethernet shield , have managed build circuit on breadboard uses 74hc4067 multiplexer open port , read input temperature sensor. it displays temperature reading on serial monitor. in sketch figured out how use web display same information. i mention give idea of skill level. the math of ohm's law makes sense me applying design of own circuits remains daunting.
so here's goal. i've built electric bike. it's being powered 72 battery cells scavenged old laptops. from reading on using these cells important match cells of equal capacity (measured in mah). difficult task used batteries. the best way charge cell , discharge it, measuring voltage drop on time calculate true capacity.
to can put large resistor on cell draw current , measure voltage drop. track on time , have need. simple enough (easy me say) single cell. but have 300 cells test. one cell @ time take forever using method.
so i'd build multi-cell discharger using 74hc4067 multiplexer read 8 or 16 inputs @ time. conceivably connect 2 multiplexers same arduino or build. multiple units test batteries in large batches. hopefully see i'm going.
the lithium ion battery i'm testing charged @ start around 4.0v (maybe 4.2v). the test draw down 3.0v, lets say. a test pull 1a , measure how long takes drop voltage (and calculate mah of cell).
here's problem. the 74hc4067 inputs supposed @ 25ma or less. if hook multiplexer across ends of resistor, won't current fry it? how measure voltage @ low current (25ma) compared drain of battery is?
somehow think if understood ohm's law better figure out i'm stumped.
if you've read entire post, patience. any tips or pointers appreciated.
p.s. have hall effect sensor?
hi , welcome.
your concern nothing worry about. '4067 output connected arduino input, high impedance. tiny current flow arduino.
i surprised understand cell charging without understanding ohm's law!
paul
your concern nothing worry about. '4067 output connected arduino input, high impedance. tiny current flow arduino.
i surprised understand cell charging without understanding ohm's law!
paul
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