[DaveC]

Several models of cordless drills have a white LED "headlight" that lights
the drill's target. I'd like to add one to my drill.

Battery voltage is 14.4.

It seems simple enough: some device senses a small voltage going to the motor
and closes a circuit from battery to LED.

What device would you use to sense and control these voltages?

Ideas?

Thanks,

 

[Ian Stirling]

Several models of cordless drills have a white LED "headlight" that lights
the drill's target. I'd like to add one to my drill.

Battery voltage is 14.4.

It seems simple enough: some device senses a small voltage going to the motor
and closes a circuit from battery to LED.

What device would you use to sense and control these voltages?

A resistor.
For added value, maybe a capacitor too.
A 10uF capacitor across the LED, and a 500 ohm resistor.
Actually, thinking about it, you'd want a bridge rectifier connected to
the motor terminals, a 420 ohm resistor between that and the
capacitor/LED.

Hmm.
If it does PWM, as it probably will, if it's not the very cheapest,
you'd want to swap that around so that the bridge is first, feeding the
capacitor (upgraded to 100uF@25V), then the resistor and LED in series.

 

[Rich Grise]

Several models of cordless drills have a white LED "headlight" that lights
the drill's target. I'd like to add one to my drill.

Battery voltage is 14.4.

It seems simple enough: some device senses a small voltage going to the motor
and closes a circuit from battery to LED.

What device would you use to sense and control these voltages?

I'd just duct-tape an LED flashlight to it.

Good Luck!
Rich

 

[GregS]

I'd just duct-tape an LED flashlight to it.

As the subject suggests, strobe the LED to make the drill stop.
I'm not sure what good this would do, but would be interesting.

greg

 

[bob mcree]

As the subject suggests, strobe the LED to make the drill stop.
I'm not sure what good this would do, but would be interesting.

greg

you could connect the led across the motor with a current regulator in
series to control the led current. you can use an lm317 3 terminal
regulator as a current regulator with just a single resistor. set the
current reg to put out the current your led needs and it will power it
appropriately any time the motor is running at an average voltage of 5v
or so which should be any time it is turning.

you could also use an npn transistor like a 2n2222 with the base
connected to the switched motor lead through a 1k or so resistor. you
would then hook the led up to the 14.4v through an appropriate current
limit resistor on the high side and the transistor making the led to
ground connection.

-bob

 

[Guns]

Buy a led with trigged included...

Regards!

 

[DaveC]

Thus spake bob mcree:

you could also use an npn transistor like a 2n2222 with the base connected to

the switched motor lead through a 1k or so resistor. you would then hook the
LED up to the 14.4v through an appropriate current limit resistor on the high

side and the transistor making the LED to ground connection.

Thanks, Bob. I think that is the sort of design I was looking for.

What about the PWM output of the motor controller turning the transistor on
and off? Is there a way to ensure that this doesn't pulse the LED?

Will a simple cap at the base keep the trans turned on? Would that interfere
with the motor control circuit (ie, the SCR, or whatever it is that controls
the motor current)?

Thanks,

 

[ehsjr]

Thus spake bob mcree:




Thanks, Bob. I think that is the sort of design I was looking for.

What about the PWM output of the motor controller turning the transistor on
and off? Is there a way to ensure that this doesn't pulse the LED?

Will a simple cap at the base keep the trans turned on? Would that interfere
with the motor control circuit (ie, the SCR, or whatever it is that controls
the motor current)?

Thanks,

This reply assumes you intend to modify the drill and
connect the LED to the drill's battery.

You *MUST* use Ian's idea of a bridge rectifier or
equivalent. The motor can go forward or reverse, so
you have to "steer" the voltage. You can use an LM317
and a resistor so that the LED always glows the same
brightness, but you'll need to add capacitors, too,
because the supply will be electrically noisy. Doubtful
you'll have the room inside for all of that.

Instead: wire the - of the led to the - lead from
the battery. Wire a resistor in series with the other
lead from the LED. Connect the other side of the
resistor to the banded ends of two 1N4148 diodes.
The other ends of the diodes go to the trigger
switch wires that go to the motor. You *might* be
able to squeeze all of that into the drill. So much
the better if you also have room to add an electrolytic
cap wired across the LED.

Since it is doubtful you will be able to mount the LED
in the drill in the first place, go with a mofification
of Rich's idea. Glue a steel plate on the drill in
an appropriate place. Use a strong magnet or two to
attach the LED flashlight to the drill. You can get
some really strong magnets that are about the size of
a small "button" battery, like catalog # MAG-80 from
http://www.allelectronics.com/

Ed

 

[DaveC]

Thus spake ehsjr:

Instead: wire the - of the led to the - lead from the battery. Wire a
resistor in series with the other lead from the LED. Connect the other side
of the resistor to the banded ends of two 1N4148 diodes. The other ends of
the diodes go to the trigger switch wires that go to the motor. You *might*
be able to squeeze all of that into the drill. So much the better if you also

have room to add an electrolytic cap wired across the LED.

Thanks, Ed. An elegant solution, as always.

There is plenty of room in the handle (above the battery) for components, but
you're right, there's no room for the LED in the body below the chuck. I plan
on adding a little JB Weld on the external of the drill body to mount an LED
holder.

Thanks again,

 

[DaveC]

Thus spake ehsjr:

So much the better if you also have room to add an electrolytic cap wired
across the LED.

Ed, what size cap would you suggest?
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC
[email protected]
This is an invalid return address
Please reply in the news group

 

[Ian Stirling]

Thus spake ehsjr:


Ed, what size cap would you suggest?

Don't wire it across the LED.
Wire it across the LED and resistor - this way it'll smooth the PWM much
better.

10uF@25V should be fine.

Whatever you can easily fit @25V, is what I'd use.

 

[Rich Grise]

Thus spake ehsjr:



Thanks, Ed. An elegant solution, as always.

There is plenty of room in the handle (above the battery) for components, but
you're right, there's no room for the LED in the body below the chuck. I plan
on adding a little JB Weld on the external of the drill body to mount an LED
holder.

http://www.copquest.com/10-4650.htm
Fifth hit at:
http://www.google.com/search?hl=en&q="tiny+LED+flashlight"

Cheers!
Rich

 

[Rich Grise]

Don't wire it across the LED.
Wire it across the LED and resistor - this way it'll smooth the PWM much
better.

10uF@25V should be fine.

Whatever you can easily fit @25V, is what I'd use.

If you're using the actual PWM, I wouldn't put a cap right at
its output, because it will affect the PWM waveform, and might
affect the operation of the drill motor. And I wouldn't put
the cap right across the LED, because it won't charge over Vf
of the LED, and won't discharge lower than Vf. (Well, it won't
discharge below Vf anyway...)

I'd use a resistor on _both_ sides of the cap. One to isolate
it from the PWM, and the other to give it a chance to hold some
charge before the LED discharges it.

IOW, if this is an exercise in drill modification and circuit-
building, then it sounds like an "interesting" project [ ;-) ],
but, if all I wanted to do is have some light to drill holes by
in dark nooks, I'd _still_ duct-tape an LED flashlight to the
drill. (or glue it, or maybe Sculpey.)

Cheers!
Rich

 

[Keith]

This reply assumes you intend to modify the drill and
connect the LED to the drill's battery.

You *MUST* use Ian's idea of a bridge rectifier or
equivalent. The motor can go forward or reverse, so
you have to "steer" the voltage.

I haven't been following this discussion, but one could also use two LEDs
anti-parallel. ...or one could take the trigger/polarity switchs (don't
have the wiring diagram) and wire it to a pair of complementary
transistors to drive the LED.

You can use an LM317
and a resistor so that the LED always glows the same
brightness, but you'll need to add capacitors, too,
because the supply will be electrically noisy. Doubtful
you'll have the room inside for all of that.

Who cares about noise? Any such noise is certainly going to be above the
flicker fusion threshold. ...or a simple capacitor (smaller than a
garbage can) isn't going to help.

Instead: wire the - of the led to the - lead from
the battery. Wire a resistor in series with the other
lead from the LED. Connect the other side of the
resistor to the banded ends of two 1N4148 diodes.
The other ends of the diodes go to the trigger
switch wires that go to the motor. You *might* be
able to squeeze all of that into the drill. So much
the better if you also have room to add an electrolytic
cap wired across the LED.

Again, what's the cap do?

Since it is doubtful you will be able to mount the LED
in the drill in the first place, go with a mofification
of Rich's idea. Glue a steel plate on the drill in
an appropriate place. Use a strong magnet or two to
attach the LED flashlight to the drill. You can get
some really strong magnets that are about the size of
a small "button" battery, like catalog # MAG-80 from
http://www.allelectronics.com/

A good idea, but doesn't answer the question asked.

 

[gnoge]

This is the best idea, because you probably want the light on before
you pull the trigger. Actually, I remember seeing one of these drill
headlamps that had its own little watch battery and pushbutton switch.

 

[DaveC]

Thus spake gnoge:

This is the best idea, because you probably want the light on before you pull

the trigger. Actually, I remember seeing one of these drill headlamps that
had its own little watch battery and pushbutton switch.

It's an exercise in drill modification and circuit design. I don't want to
just "tag something on" as it will interfere with the drill's fit in its
vacuum-molded case, and it'll be one more thing I'll have to think about:
shutting off and dismounting the light before packing the drill.

I'll probably try Ed's idea with 2 diodes running from the motor leads to the
LED. Some combination of resistor(s) and cap will be tried also, as needed.

As far as needing light before beginning drilling, I note that power runs to
the motor at the slightest pull of the trigger, which rotates the motor
imperceptibly, if at all. So with this design I will have light before I spin
up the motor for drilling.

Other approaches of circuit design are still welcome. I haven't unholstered
the soldering iron yet!

Thanks,

 

[ehsjr]

I haven't been following this discussion, but one could also use two LEDs
anti-parallel. ...or one could take the trigger/polarity switchs (don't
have the wiring diagram) and wire it to a pair of complementary
transistors to drive the LED.




Who cares about noise?

The LED will, if/when it burns out. The LM317 behaves
badly when there's noise & no caps. It won't deliver
constant current to the LED, so the brightness will
vary, negating the reason for using the LM317 in
the first place.

Any such noise is certainly going to be above the

flicker fusion threshold. ...or a simple capacitor (smaller than a
garbage can) isn't going to help.

Of course it will. Look at the LM317 datasheet.

Again, what's the cap do?

Poorly stated. Intended was across the series R & LED.
Reduces flicker.

A good idea, but doesn't answer the question asked.

The question asked was already answered. Is there a
problem with providing alternative ideas ?

Ed

 

[Paul Hovnanian P.E.]

Thus spake gnoge:



It's an exercise in drill modification and circuit design. I don't want to
just "tag something on" as it will interfere with the drill's fit in its
vacuum-molded case, and it'll be one more thing I'll have to think about:
shutting off and dismounting the light before packing the drill.

I'll probably try Ed's idea with 2 diodes running from the motor leads to the
LED. Some combination of resistor(s) and cap will be tried also, as needed.

As far as needing light before beginning drilling, I note that power runs to
the motor at the slightest pull of the trigger, which rotates the motor
imperceptibly, if at all. So with this design I will have light before I spin
up the motor for drilling.

Other approaches of circuit design are still welcome. I haven't unholstered
the soldering iron yet!

Here's a thought: Install two contacts on the face of the trigger switch
and make a touch switch. Using a Mosfet and a couple of resistors, the
conduction through your finger will be enough to turn on the LED by
touching the trigger. I'd post a ckt, but you can Google a bunch of them
faster than I can hack ASCII line art.

Of course, this won't work if you wear gloves while operating the drill.

 

[Paul Hovnanian P.E.]

While you're at it, get two of those LED lasers that have the optics to
put out a line instead of a spot. Mount them at right angles so that
they put out an alignment cross just beyond the drill tip.

The mounting method will have to incorporate some means of lateral
adjustment to 'bore site' the beams.