Since your circuit obviously lets you control what LEDs are on at what time,
you could probably just reduce the on-time percentage to proportionally
reduce power draw.

Bob Ammerman
RAm Systems

----- Original Message -----
From: "Fred Hillhouse" <fmhillhouse@COMCAST.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Friday, June 04, 2004 3:36 PM
Subject: Re: [PIC:] First Project Finished! But... it used up all my bat
tree


> You shouldn't connect every LED through one resistor.
>
> What are your LEDs rated at? What is the forward voltage?
>
> If you have 5ma LEDs and the forward voltage is 1.2v, then a resistor of
760
> ohms [(5V-Vforward)/.005=resistance] should be in series with the LED. If
> you are using a transistor to turn them on, then you will need to also
> account for the voltage drop across the transistor.
>
> The purposes of multiplexing the LEDs are less parts and less current.
>
> Something else to consider: if you are using 20ma LEDs and they are all
> connected to you PIC, then if they all turn on, you can exceed to overall
> current rating of the PIC. Even though each pin can sink/source 25ma, all
of
> them can't at the same time.
>
>
>
>
> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Lindy Mayfield
> Sent: Friday, June 04, 2004 3:15 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC:] First Project Finished! But... it used up all my bat
> tree
>
>
> I connected my multimeter from +5 on the battery to the circuit and it
reads
> about 75 mAmps.  I'm quite new to this, but that seems like a lot.
>
> Since all the LED's are connected to a common ground in my circuit
(already
> soldered), can I add a resistor between the cathode of the LED's to the
> battery ground?
>
> -----Original Message-----
> From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]
On
> Behalf Of Fred Hillhouse
> Sent: Friday, June 04, 2004 21:11
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC:] First Project Finished! But... it used up all my bat
> tree
>
> Although many LED clocks have 9V batteries in them, usually the LEDs are
off
> if the AC power fails for some reason. The 9V battery only powers the
'time
> keeping' circuit, not the 'time displaying' circuit.
>
> You may want to consider a 9V wall wart instead.
>
>
>
> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Lindy Mayfield
> Sent: Friday, June 04, 2004 2:48 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [PIC:] First Project Finished! But... it used up all my bat
> tree
>
>
> Hi Guys.
>
> I finished my first project!  Finally.  I got the idea from Mike Predeko's
> book for the LED clock.  But I couldn't find the right parts to put
together
> the multiplexing for all the LED's, so I decided to work with what I have
> available and made a binary clock:  20 small 3mm LED's that show the
hours,
> minutes, and seconds in bcd binary.
>
> The design so far is simply a 9v battery, a 5v voltage regulator, a PIC
> 16f877, a 32.768 kHz crystal + 2 22pf caps, resistors and LED's, and one
> resistor tied to MCLR.
>
> The programming was fun.  Building and soldering the rat's nest out of
wires
> on the back of the board wasn't.  (-:  (Took 3 weeks.)
>
> I left it running for a test last night and it sucked all the juice out of
> my 9 volt battery in just a few hours.
>
> Would someone give me hints as to how to figure out what the problem is
why
> it is using so much power?
>
> Thanks in advance.
> Lindy
>
>
>
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