Current Detecting Circuit

Fully integrated Hall Effect Based Linear Current Sensor

Digikey

Sensor

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

Sensor

Naaaah! You need some bailing wire ;-)

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

| 1962 | America: Land of the Free, Because of the Brave

Sensor

And duct tape. Nothing beats duct tape... 8-)

Charlie

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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

Sensor

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

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
         America: Land of the Free, Because of the Brave

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.)

--
Cats, coffee, chocolate...vices to live by

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...

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

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.

1. 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

=EF=BF=BD =EF=BF=BD =EF=BF=BD =EF=BF=BD =EF=BF=BD =EF=BF=BD =EF=BF=BD =EF=BF= =BD =EF=BF=BD =EF=BF=BD =EF=BF=BD =EF=BF=BD =EF=BF=BD ...Jim Thompson

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

Those chips have soberingly-high DC offset specs.

Jim Thompson snipped-for-privacy@My-Web-Site.com posted to sci.electronics.design:

But then it would be conduct tape.

*groan* :P .... :)

D from BC

"Jim Thompson" skrev i en meddelelse news: snipped-for-privacy@4ax.com...

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