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Current Sensors

I

Inspar8r

I have a question about a design problem i need to address.

I designed and built a set of LED taillights for my car. Obviously,
the LEDs draw significantly less than a standard bulb.

The problem is, there is a circuit that is designed to monitor the
bulbs, and illuminates a light in the cluster when the bulb fails.
Right now, it thinks my LEDs are failed bulbs.

I am not satisfied or comfortable with wiring up parallel 6© 10W
resistors for the taillights and 47© 25W resistors for the brake
light circuits just to mimick the standard bulb (as well as dissipate
almost 1A of current as heat every time the brakes are applied).
Removing the bulb is not an option either. Most have told me that b/c
they are LEDs, i don't need to monitor the circuit, but i'd like to
anyway (you never know)...

The failure sensor is a CURRENT sensing device, and according to the
schematic, uses an OR-gate that signals a npn transistor that powers
the warning light. The OR-gate is fed by 2 unidentified "boxes" (i'm
guessing IC's). I think the OR-gate is there to allow the failure
sensor to monitor the tails both when the car is in ACC and when
started.

My question is, where can i find schematics on IC current sensors that
i can tailor to my needs to build my own sensor and just bypass the
stock sensor?

If I knew what those unknown boxes where, i would modify the stock box
to "look" for less current.

Any ideas...
*---------------------------------*
Posted at: http://www.GroupSrv.com
Check: http://wwww.HotCodecs.com
*---------------------------------*
 
R

Robert Baer

Inspar8r said:
I have a question about a design problem i need to address.

I designed and built a set of LED taillights for my car. Obviously,
the LEDs draw significantly less than a standard bulb.

The problem is, there is a circuit that is designed to monitor the
bulbs, and illuminates a light in the cluster when the bulb fails.
Right now, it thinks my LEDs are failed bulbs.

I am not satisfied or comfortable with wiring up parallel 6© 10W
resistors for the taillights and 47© 25W resistors for the brake
light circuits just to mimick the standard bulb (as well as dissipate
almost 1A of current as heat every time the brakes are applied).
Removing the bulb is not an option either. Most have told me that b/c
they are LEDs, i don't need to monitor the circuit, but i'd like to
anyway (you never know)...

The failure sensor is a CURRENT sensing device, and according to the
schematic, uses an OR-gate that signals a npn transistor that powers
the warning light. The OR-gate is fed by 2 unidentified "boxes" (i'm
guessing IC's). I think the OR-gate is there to allow the failure
sensor to monitor the tails both when the car is in ACC and when
started.

My question is, where can i find schematics on IC current sensors that
i can tailor to my needs to build my own sensor and just bypass the
stock sensor?

If I knew what those unknown boxes where, i would modify the stock box
to "look" for less current.

Any ideas...
*---------------------------------*
Posted at: http://www.GroupSrv.com
Check: http://wwww.HotCodecs.com
*---------------------------------*


----------------------------------------------------------

----------------------------------------------------------
color]

It seems you are correct; the unknown sensing method is the problem
that needs to be solved.
Since the stuff you know about is standard logic, one can ignore that.
Work on the assumption that a current sensing resistor is used to
develop a voltage for the "box" which amplifies that voltage to drive a
comparitor (level sensor) which ten drives the logic.
On that basis, all you care about is to find that resistor, and
replace it witha larger vale.
Say the sense trigger point is one amp, and a reasonable trigger value
for the LED lamp replacement is 0.1 amp.
Then one would increase the value of the sense resistor by a factor of
ten.
Click to expand...
 
I

Inspar8r

Thanks for the info...

Here's a cutout of the box i'm looking at..

Pin 3 is the power coming from the car in ACC/ON mode
Pin 8 is the power coming from the car when STARTED
Pin 11 is ground
Pin 7 goes to my taillights.

Is that lone resistor the one setting up the current for the sensor?

Or do you really need to know what those to little boxes are (i'm
guessing ICs)??

Thanks for the help so far..
*---------------------------------*
Posted at: http://www.GroupSrv.com
Check: http://wwww.HotCodecs.com
*---------------------------------*
 
S

SCADA

Inspar8r said:
Thanks for the info...

Here's a cutout of the box i'm looking at..

Pin 3 is the power coming from the car in ACC/ON mode
Pin 8 is the power coming from the car when STARTED
Pin 11 is ground
Pin 7 goes to my taillights.

Is that lone resistor the one setting up the current for the sensor?

Or do you really need to know what those to little boxes are (i'm
guessing ICs)??

Thanks for the help so far..
*---------------------------------*
Posted at: http://www.GroupSrv.com
Check: http://wwww.HotCodecs.com
*---------------------------------*


----------------------------------------------------------

----------------------------------------------------------
color]

I'm thinking that there must be an additional pin to light the dash
indication of a failed bulb! Or perhaps pin 3 or 8 is that indication but
you read 12VDC through the bulb!
That being the case, it may be easier to design your own circuit rather than
reverse engineer that one. If you have the DC input (12V) the output (tail
lamp) and the indication circuit (?) than you have all you need to design
the circuit. Either use a shunt resistor in series with the +12V to tail
lamp and measure the drop across a differential amp, or use a "High side"
current sensor chip. Interface the output to the indication circuit.
Click to expand...
 
B

beast

Since LED's don't burn out, why not just neutralise the sensors?

Or that IC is probably a low voltage box, why not wire the output of
the LED directly into the box?
*---------------------------------*
Posted at: http://www.GroupSrv.com
Check: http://www.HotCodecs.com
*---------------------------------*
 
S

SteveB

There's also the problem that a failed LED doesn't necessarily take a lower
or zero current, it may even take more when it fails.
 
Y

Yukio

A: I have seen circuits that just use a couple of turns of wire over a
REED switch to sense DC currents in the milli-amp/amps. range with
virtually no voltage drop ! for greater sensitivity just add more turns, for
more capacity use heavier wire !
B: On several automobiles , I know that the Tail-lights are fed off the
same circuit as the Dash-board fuse, ie, if the tail-light fuse fails, the
dash-light will not turn on !


Yukio YANO
I have a question about a design problem i need to address.

I designed and built a set of LED taillights for my car. Obviously,
the LEDs draw significantly less than a standard bulb.

The problem is, there is a circuit that is designed to monitor the
bulbs, and illuminates a light in the cluster when the bulb fails.
Right now, it thinks my LEDs are failed bulbs.

I am not satisfied or comfortable with wiring up parallel 6© 10W
resistors for the taillights and 47© 25W resistors for the brake
light circuits just to mimick the standard bulb (as well as dissipate
almost 1A of current as heat every time the brakes are applied).
Removing the bulb is not an option either. Most have told me that b/c
they are LEDs, i don't need to monitor the circuit, but i'd like to
anyway (you never know)...

The failure sensor is a CURRENT sensing device, and according to the
schematic, uses an OR-gate that signals a npn transistor that powers
the warning light. The OR-gate is fed by 2 unidentified "boxes" (i'm
guessing IC's). I think the OR-gate is there to allow the failure
sensor to monitor the tails both when the car is in ACC and when
started.

My question is, where can i find schematics on IC current sensors that
i can tailor to my needs to build my own sensor and just bypass the
stock sensor?

If I knew what those unknown boxes where, i would modify the stock box
to "look" for less current.

Any ideas...
*---------------------------------*
Posted at: http://www.GroupSrv.com
Check: http://wwww.HotCodecs.com
*---------------------------------*
Click to expand...
 
I

Inspar8r

Here's the schematics I drew up..

PLEASE NOTE BEFORE READING!!!!!!!!

The IC a drew is the way it would look if you were looking AT THE
BOTTOM OF THE IC, WITH THE NOTCH CLOSEST TO YOU.

The harness connector is the pin asignments as if you were looking
DIRECTLY AT THE HARNESS CONNECTOR.

The harness PLUG is the pin assignments as if you were looking
DIRECTLY AT THE PLUG. Try no to get confused. The best way to
remember is to match up the "X's", since they denote a terminal that
is UNUSED.

Hopefully you can understand my notes...

Oh and C1, C2, C3 are all .047µf Ceramic Discs. I forgot to ge tthe
values of C4 and C5, but i don't think it matters much.
http://mmsport.s5.com/IS300/LED/Sensor schematic.jpg
*---------------------------------*
Posted at: http://www.GroupSrv.com
Check: http://www.HotCodecs.com
*---------------------------------*
 
B

beast

The pin that indicates "lights on" should be 3V to 5V if it's a
standard digital voltage, then the pin that triggers the dash light
should be hot. So you run the 3V photocell to the sensor array,
whichever one it is.

I think your unknown boxes are sensor arrays.
 
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