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'[OT] ?: LED With only one battery'
1998\01\14@021731 by Pasi T Mustalahti

picon face
Trying to run a PIC 16F84 with 2V i came to tihnk if there is any
possibilities to make a LED to run with only one NiCd that has the output
valtage of about 1.2 V. Led needs about 1.6 V.
The system should not have any fancy IC's and it should fit in the size of
half of an AAA-cell.

Virtual beer for the best idea !

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1998\01\14@044814 by Steve Baldwin

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face
> Trying to run a PIC 16F84 with 2V i came to tihnk if there is any
> possibilities to make a LED to run with only one NiCd that has the output
> valtage of about 1.2 V. Led needs about 1.6 V.
> The system should not have any fancy IC's and it should fit in the size
of
> half of an AAA-cell.

A couple of transistors/FETs and a capacitor to make a charge pump doubler.

Steve.

======================================================
 Very funny Scotty.  Now beam down my clothes.
======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680                email: stevebspamKILLspamkcbbs.gen.nz
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1998\01\14@050644 by Keith Howell

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face
Check out the LM3909 LED flasher chip. 8-pin DIP package.
By National Semiconductor.
Developed for toys flashing a LED from a single cell.
It uses the timing capacitor to increase the voltage to the LED.
Data sheet shows internal circuit.
You may be able to implement it with a few discretes,
but it's not worth the effort unless you're making
many gadgets.

1998\01\14@051726 by William Chops Westfield

face picon face
   Trying to run a PIC 16F84 with 2V i came to tihnk if there is any
   possibilities to make a LED to run with only one NiCd that has the output
   valtage of about 1.2 V. Led needs about 1.6 V.
   The system should not have any fancy IC's and it should fit in the size of
   half of an AAA-cell.

An LM3909 "LED Flasher" charges a cap and then discharges it in series with
the battery to drive an LED from a single cell.  While the "normal"
configuration uses a 300uF cap and flashes once a second, presumably
(haven't tried it) a smaller cap would result in a faster rate, perhaps up
to the "apparently continuously on".  Might be awfully dim, though - it's
none too bright in the original config.  About $1 for the chip - the circuit
would fit in your space if you can find SOIC versions.

You might be able to achieve the same sort of thing with a couple
transistors, some IO pins and some intelligent software (sorta like a
standard AC voltage doubler driven by IO pins, which might work too, for
high efficiency LEDs...)

BillW

1998\01\14@060957 by REMOVE_TO_REPLY_jnlrich

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face
Try this:

  PIC Output pin
        |
  +-----+------+
  }            |
  |            |
  |           ---
  |           ---    .1 to 2.2 uFd - value depends on drive pulse
  |            |                     rate, use smaller value with
  |            |                     higher rates        
  |            |        
  \            \
  / 1K         /
  \            \      10-100 Ohms - may not even be needed.
  /            /                     Limits peak current
  \            \                     from output pin.
  |            |
  |            |
  |     /------+
  |  | /       | //
  |  |/       ---  
  +--|   LED  / \    
     |\|      ---  
     | \       |      
2N3904  |      |  
        |      |
       ---    ---
       ///    ///

The LED will appear to be on solid when the pulse rate is more
than 30 per second.



On Wed, 14 Jan 1998 09:16:58 +0200, you wrote:

->Trying to run a PIC 16F84 with 2V i came to tihnk if there is any
->possibilities to make a LED to run with only one NiCd that has the
output
->valtage of about 1.2 V. Led needs about 1.6 V.
->The system should not have any fancy IC's and it should fit in the
size of
->half of an AAA-cell.
->
->Virtual beer for the best idea !
->
->--------------------------------------------------------------------------
->PTM, .....pasi.mustalahtiKILLspamspam.....utu.fi, EraseMEptmustaspam_OUTspamTakeThisOuTutu.fi,
http://www.utu.fi/~ptmusta
->Lab.ins. (mikrotuki) ATK-keskus/Mat.Luon.Tdk
OH1HEK
->Lab.engineer (PC support) Computer Center
OI7234
->Mail: Turun Yliopisto / Fysla, Vesilinnantie 5, 20014
->Pt 02-3336669, FAX 02-3335632 (Pk 02-2387010, NMT 049-555577)
->--------------------------------------------------------------------------

1998\01\14@064341 by Ian Stirling

flavicon
picon face
>
> Trying to run a PIC 16F84 with 2V i came to tihnk if there is any
> possibilities to make a LED to run with only one NiCd that has the output
> valtage of about 1.2 V. Led needs about 1.6 V.
> The system should not have any fancy IC's and it should fit in the size of
> half of an AAA-cell.
>
> Virtual beer for the best idea !

Don't know if this mail message will work...
However, I've done this, it's not too hard.
What I did.
Take small pot-core, break/sand to get a toroid of 3mm*1mm*1mm
Wrap with fine wire, to get a reasonable inductance (I picked
200Khz, and 60ma max current).
Then you need a way of switching this coil, at 200Khz or so.
I picked a multivibrator, as it was simplest, and diddn't require
much thinking to get working.
One end of one collector resistor was connected directly (IIRC) to
the base of the switching transistor.
The LED became it's own diode.
IIRC, efficiancy was around 85%.

I posted on this on misc.sirvivalism, dejanews should pick it up.
Final size was around 3mm long, and the diameter of an AAA cell, it
went in space made by extra compression of the spring, in a single
AAA cell light.
Transistors were surface mount, and the other components were mounted
round them, using fine enameled wire, which fluxes when soldered to.
Need a magnifying glass :)

1998\01\14@085456 by Lynn Richardson

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face
Sorry, guy, my brain misfired this morning.
The ciruit should have been:

  PIC Output pin
        |
  +-----+------+
  |            |
  |            |
  |           ---
  |           ---    .1 to 2.2 uFd - value depends on drive pulse
  |            |                     rate, use smaller value with
  |            |                     higher rates
  |            |
  \            \
  / 1K         /
  \            \      10-100 Ohms - may not even be needed.
  /            /                     Limits peak current
  \            \                     from output pin.
  |            |
  |            |
  |     /------+
  |  | /       | //
  |  |/       ---
  +--|   LED  / \
     |\|      ---
     | \       |
2N3904  |      |
        |      |
       ---   (VCC)
      ///
               ^
Note the LED anode now connects to VCC, instead of VSS.

At 11:01 AM 1/14/98 GMT, in a state of severe coffee deprivation,
Lynn Richardson wrote:
{Quote hidden}

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1998\01\14@115003 by John Halleck

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face
On Wed, 14 Jan 1998, Pasi T Mustalahti wrote:

> Trying to run a PIC 16F84 with 2V i came to tihnk if there is any
> possibilities to make a LED to run with only one NiCd that has the output
> valtage of about 1.2 V. Led needs about 1.6 V.

 I flash a 2.0 LED on a 1.2 V battery all the time.
 The 3909 chip does the job...   And the idea behind it seems quite "Pic"able.
 Just charge a cap, and then put it in series with the battery.

{Quote hidden}

1998\01\15@080609 by Pasi T Mustalahti

picon face
PTM: This was not exactly what I was looking for, but I liked it.
So, here you got some beer from Finland (and some foreign
too)
http://www.hartwall.fi/new/merkit_frameset.html

73 de OH1HEK


On Wed, 14 Jan 1998, Lynn Richardson wrote:

{Quote hidden}

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PTM, RemoveMEpasi.mustalahtispamTakeThisOuTutu.fi, ptmustaEraseMEspam.....utu.fi, http://www.utu.fi/~ptmusta
Lab.ins. (mikrotuki) ATK-keskus/Mat.Luon.Tdk                    OH1HEK
Lab.engineer (PC support) Computer Center                       OI7234
Mail: Turun Yliopisto / Fysla, Vesilinnantie 5, 20014
Pt 02-3336669, FAX 02-3335632 (Pk 02-2387010, NMT 049-555577)
--------------------------------------------------------------------------

1998\01\16@075724 by paulb

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face
Pasi T Mustalahti wrote:

> PTM: This was not exactly what I was looking for, but I liked it.

 Well, I certainly didn't like the original.  I am still very
suspicious of the circuit published.  Transistors still have some gain
with emitter and collector reversed.  Unless the 2N3904 is somehow
immune to this (and I am SURE I have seen it deliberately used "upside-
down" somewhere to achieve a low saturation votage), when the PIC output
pin having been high and charged the capacitor, goes to ground, will it
not bias the transistor on so as to discharge the capacitor "up" to
ground as soon as the transistor's nominal collector falls 0.7V below
ground?

 Perhaps the LED will conduct first at 1.7V which is only 0.5V below
ground with a Vcc of 1.2V, but this is a bit close.  If the LED requires
2.0V, you are going to lose current through the transistor.

It would be simpler to replace the transistor with a Schottky diode.

 Cheers,
       Paul B.

1998\01\16@075727 by paulb

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face
William Chops Westfield wrote:

> An LM3909 "LED Flasher" charges a cap and then discharges it in series
> with the battery to drive an LED from a single cell.  While the
> "normal" configuration uses a 300uF cap and flashes once a second,
> presumably (haven't tried it) a smaller cap would result in a faster
> rate, perhaps up to the "apparently continuously on".  Might be
> awfully dim, though - it's none too bright in the original config.

 It can be brightened by shunting the time constant resistors with a
much lower value (original is as I seem to recall, two 5k steps).  The
problem I have with it is that there is no actual "enable" pin; the
series pair of said resistors is internally connected in place so you
can decrease the fixed resistance but not increase or open it.

 Consequently, the only way to switch it on and off is to use the PIC
to feed power to it, adding the PIC I/O resistance to any other losses.

 Cheers,
       Paul B.

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