Current Detecting Circuit

[Matt]

I am looking for some help for my senior design project. I am not an
electrical engineer, however I will need a simple circuit for my
project.

This is what we would like to do:
We are running a 12 volt drill motor off of batteries and we would
like to detect the current used by the drill motor, and illuminate an
LED when the motor draws more than some arbitrary cutoff current and
extinguish the LED when the current is below a the same value.

I'm guessing this will require an op amp, but I haven't taken circuits
yet, so I don't know much more than that.

Thanks in advance for any help you might be able to provide.

-Matt

 

[D from BC]

I am looking for some help for my senior design project. I am not an
electrical engineer, however I will need a simple circuit for my
project.

This is what we would like to do:
We are running a 12 volt drill motor off of batteries and we would
like to detect the current used by the drill motor, and illuminate an
LED when the motor draws more than some arbitrary cutoff current and
extinguish the LED when the current is below a the same value.

I'm guessing this will require an op amp, but I haven't taken circuits
yet, so I don't know much more than that.

Thanks in advance for any help you might be able to provide.

-Matt

Fully integrated Hall Effect Based Linear Current Sensor
http://www.allegromicro.com/en/Products/Part_Numbers/0712/0712.pdf
Digikey <$2.00

...add comparator.


D from BC

 

[[email protected]]

Fully integrated Hall Effect Based Linear Current Sensorhttp://www.allegromicro.com/en/Products/Part_Numbers/0712/0712.pdf
Digikey <$2.00

WHAT!? You're not going to build your own out of old chewing gum and
underwear???

 

[Jim Thompson]

WHAT!? You're not going to build your own out of old chewing gum and
underwear???

Naaaah! You need some bailing wire ;-)

...Jim Thompson

 

[Charlie Edmondson]

Naaaah! You need some bailing wire ;-)

...Jim Thompson

And duct tape. Nothing beats duct tape...

Charlie

 

[D from BC]

And duct tape. Nothing beats duct tape...

Charlie

Electronics homebrew style

Resistors : BBQ charcoal
Capacitors: Cooking foil, paper towels and peanut oil
Inductors: Coat hanger wire
Amplifiers: Maybe dual filament automotive bulbs
PCB's: Cooking foil on Arborite laminate
Wire: Salt water in plastic tubing.
Battery: Lemons and dissimilar metals
Circuit simulator: paper


D from BC

 

[Jim Thompson]

Electronics homebrew style

Resistors : BBQ charcoal
Capacitors: Cooking foil, paper towels and peanut oil
Inductors: Coat hanger wire
Amplifiers: Maybe dual filament automotive bulbs
PCB's: Cooking foil on Arborite laminate
Wire: Salt water in plastic tubing.
Battery: Lemons and dissimilar metals
Circuit simulator: paper


D from BC

Extra points if the current flows thru the duct tape ;-)

...Jim Thompson

 

[Ecnerwal]

Extra points if the current flows thru the duct tape ;-)

That can be arranged. Nothing like a 50 KV supply and a supposed
insulator (some are quite good - I recall getting to 30 KV with normal,
non-high-voltage heat shrink, - probably 3M, not some offbrand. Been a
few decades.)

 

[Alex]

I am looking for some help for my senior design project. I am not an
electrical engineer, however I will need a simple circuit for my
project.

This is what we would like to do:
We are running a 12 volt drill motor off of batteries and we would
like to detect the current used by the drill motor, and illuminate an
LED when the motor draws more than some arbitrary cutoff current and
extinguish the LED when the current is below a the same value.

I'm guessing this will require an op amp, but I haven't taken circuits
yet, so I don't know much more than that.

Thanks in advance for any help you might be able to provide.

-Matt

if it do not have to be scientific precision , a resistor in the
current path could do it, with a transistor base and emitter at the
ends of resistor and the transistor collector with a resistor to
limit LEd current could do...

 

[Matt]

Thanks for all the suggestions. I'm outta charcoal and my duct tape is
running low, so I think I might just go with the hall effect sensor.

I think some of those homebrew solutions might just work ;-)

-M

 

[Paul Mathews]

I am looking for some help for my senior design project. I am not an
electrical engineer, however I will need a simple circuit for my
project.

This is what we would like to do:
We are running a 12 volt drill motor off of batteries and we would
like to detect the current used by the drill motor, and illuminate an
LED when the motor draws more than some arbitrary cutoff current and
extinguish the LED when the current is below a the same value.

I'm guessing this will require an op amp, but I haven't taken circuits
yet, so I don't know much more than that.

Thanks in advance for any help you might be able to provide.

-Matt

The Allegro chip provides isolation, which you probably don't need if
you're going to run your detection and LED circuits off of the drill
battery anyway. You can monitor current with a series resistor and a
comparator alone. You may want to slow down the circuit so that it
doesn't respond to the current spikes that you're likely to have with
most any motor and speed control circuit. The circuit can be as simple
as this description:
1. Comparator open-collector output (*e.g., LM311) drives LED with
series limiting resistor.
2. Choose comparator with included reference or generate a reference
voltage with a zener or a forward-biased junction. A resistor divider
presents a low reference voltage (say 100 mV) to the + comparator
input. You may want some positive feedback.
3. Battery - is system ground. Motor current from Motor - passes
through Rs. Rs = 100 mV / Ithreshold. For example, for 10 amps, Rs =
10 milliohms.
4. The comparator - input connects to the high side of Rs.

Paul Mathews

 

[D from BC]

The Allegro chip provides isolation, which you probably don't need if
you're going to run your detection and LED circuits off of the drill
battery anyway. You can monitor current with a series resistor and a
comparator alone. You may want to slow down the circuit so that it
doesn't respond to the current spikes that you're likely to have with
most any motor and speed control circuit. The circuit can be as simple
as this description:
1. Comparator open-collector output (*e.g., LM311) drives LED with
series limiting resistor.
2. Choose comparator with included reference or generate a reference
voltage with a zener or a forward-biased junction. A resistor divider
presents a low reference voltage (say 100 mV) to the + comparator
input. You may want some positive feedback.
3. Battery - is system ground. Motor current from Motor - passes
through Rs. Rs = 100 mV / Ithreshold. For example, for 10 amps, Rs =
10 milliohms.
4. The comparator - input connects to the high side of Rs.

Paul Mathews

Probably the only reason why I like the Allegro chip is that there's
no hot current sensing resistor in a circuit that depends on it's
resistance value.


D from BC

 

[mpm]

Electronics homebrew style

Resistors : BBQ charcoal
Capacitors: Cooking foil, paper towels and peanut oil
Inductors: Coat hanger wire
Amplifiers: Maybe dual filament automotive bulbs
PCB's: Cooking foil on Arborite laminate
Wire: Salt water in plastic tubing.
Battery: Lemons and dissimilar metals
Circuit simulator: paper

D from BC- Hide quoted text -

- Show quoted text -

Don't forget the "hard drive": - Coffee can and paperclips.

 

[Winfield Hill]

Probably the only reason why I like the Allegro chip is that there's
no hot current sensing resistor in a circuit that depends on it's
resistance value.

D from BC

Those chips have soberingly-high DC offset specs.

 

[JosephKK]

Jim Thompson [email protected] posted to
sci.electronics.design:

Extra points if the current flows thru the duct tape ;-)

...Jim Thompson

But then it would be conduct tape.

 

[D from BC]

Jim Thompson [email protected] posted to
sci.electronics.design:


But then it would be conduct tape.

*groan*
.....


D from BC

 

[Frithiof Andreas Jensen]

Naaaah! You need some bailing wire ;-)

Combined effort: One *could* probably make some kind of reed-relay out of
two pieces of bailing wire fixed in the chewing gum and actually get it to
work!

 

[Michael A. Terrell]

Combined effort: One *could* probably make some kind of reed-relay out of
two pieces of bailing wire fixed in the chewing gum and actually get it to
work!

Use barb wire, if you need a latching relay.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida