Driving a simple numeric LCD display is easy from any microcontroller, with very low power: http://www.ubasics.com/driving_static_lcds With a two digit display counting from 32 to 0 you need 12 output lines, and they will need to change state about 30-60 times a second. Put them on an interrupt, and put the processor to sleep, and it'll consume less than 1mA for the LCD and timer. The USB function of the microcontroller can be turned off until you detect 5V on the USB V+ line. So the only current you'll need beyond 1mA is the current required to activate that external signal you mention. The PIC18F24J50 might be agood candidate. It has more than enough pins to drive the LCD and talk via USB, it's part of the extra low power line of microchip's parts, built in real time clock/counter. It has a high precision internal oscillator to the USB, and a low speed internal oscillator which you can use for the timer/clock and for low power LCD driving. And it's relatively inexpensive. The MAX1555 IC is good for lithium-ion charging. It'll accept charging from either a USB port or from a 3.7-7V input (solar cell, for instance) and performs all the work required for safely charging the cell. You can get it on a breakout board here: http://www.sparkfun.com/commerce/product_info.php?products_id=3D726 That may help with hardware selection, but the hardware design and more difficult software design still lie ahead. If the system is as simple as you suggest, then using the USB libraries provided by microchip and just adding your LCD/timer/external output code should be relatively easy. On Mon, Nov 30, 2009 at 9:36 AM, patrickdel1982 wro= te: > > =95 =A0 =A0 =A0 My objective is to create a battery-operated counter-cont= roller which shuts > down an external function =93X=94 via an analog signal after one cycle of > thirty-two (32) days (e.g. 2764800 seconds) unless the counter-controller= is > =93unlocked=94 through a security code is entered through a USB port to r= enew > the count. > =95 =A0 =A0 =A0 The unit should be able to display the number of days lef= t in the counting > cycle on a small LCD, starting from thirty-two (32) days and counting down > to zero (0). > =95 =A0 =A0 =A0 The external function is run through a PIC16F785, which h= as an available > analog input. =A0There should be a string of five (5) security codes stor= ed on > the counter-controller memory which repeat every five (5) cycles. > =95 =A0 =A0 =A0 The counter-controller should be as low-power, running as= few watts as > possible. =A0The system should also work on a 3.0-4.0 volt range (single > lithium-ion battery). > =95 =A0 =A0 =A0 The default mode for if the battery has low power below 3= .0V is, =93locked, > but not counting,=94 meaning that the external device cannot function but= the > counter-controller stops counting for the time being until the battery is > charged above 3.0V. > =95 =A0 =A0 =A0 Since the unit is solar powered, the entire counting and = controlling > regime must be super low-power. =A0There is a switch which a human user w= ill > push periodically (perhaps 3-20 times per day) to activate and deactivate > the external function =93X,=94 so a count check, date display and control > function can be hypothetically performed only at these times. > =95 =A0 =A0 =A0 As a side note, the USB port used to unlock the system sh= ould use its > external 5V power source to charge the battery while unlocking. > > My experience with microcontrollers, counters and IC=92s is limited, havi= ng a > fair working knowledge of 8-bit MCUs, perhaps able to debug codes written= in > C format, but not a true designer or troubleshooter. =A0Overall I am a > beginner level with microcontrollers, but have a good working knowledge of > circuit design. =A0I know how to =93flash an LED.=94 =A0In fact, I can ma= ke an LED > run on PWM using 16F785. =A0Can anyone give me a recommendation of where = to > start? =A0I am interested in PIC microcontrollers, but not strictly limit= ed if > nothing fits the design parameters above. > Here is a basic diagram of the functionality of the counter-controller: > > > > > > > > > > > > http://old.nabble.com/file/p26575712/simple_diagram.jpg > > http://imgur.com/g2eg1 > > > Can anyone offer any help with what PIC families and features I should lo= ok > for? =A0Is there any PIC which has both LCD and USB capability? =A0How mu= ch > memory will I need? =A0How can I find a PIC or incorporate a design that = will > fulfill all of the above requirements? =A0What approach should I use on t= his > design? =A0Any ideas or tips? > > -- > View this message in context: http://old.nabble.com/Experimental-LCD-USB-= Solar-Design-tp26575712p26575712.html > Sent from the PIC - [PIC] mailing list archive at Nabble.com. > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist