What do you suggest?To get a boosted output of 5V at 300mA, the little 3V battery must produce 575mA which would be a lot of current for two much larger AA alkaline cells. As the battery voltage drops then the booster must use more battery current.
Two AA cells might last for 1 hour.
I'm not getting the 5V and 300mA from the coin but from a boost converterYou are NOT going to get 5V 300mA from a 3V coin battery unless it's the size of a pizza.
Power in = power outI'm not getting the 5V and 300mA from the coin but from a boost converter
But all the energy ultimately comes from your primary power source...However, I would be powering PIC microcontroller (uC) from the booster while the LEDs from the uC.
Yes, but you can't create energy from thin air as Dennis and others have said. You simply don't have enough energy storage in a coin cell, booster or no booster, to power a scrolling LED display.I'm not getting the 5V and 300mA from the coin but from a boost converter
Dear Eric,hi Exjay,
Options..
E
See you've fallen into the trap of saying how it works rather than what its pure function is...I want to build a charlieplexed LED badge with 90 LEDS. Each LED is 2mA, a low power LED.
The LEDs to be run from PIC uC. I want the overall package to be so small that it can be attached to small pocket. I intend to use 18×5 for the LED combination. All LEDs are red.
Thanks for the analysis. Can't I use a PIC with 16 pins? The pins to be used is just 10 pins. I want the design to be simple.See you've fallen into the trap of saying how it works rather than what its pure function is...
But no matter, lets run some math...
18 x 5 red LED @ forward voltage of 1.7v and current of 2mA with, say, on average 12 of the 18 on at once (strobing on the 5-led direction) requires 1.7v * 2mA * 12 mW = 41mW. Driven from 3.3v via resistors loses another (3.3 - 1.7) * 2 * 12 mW = 38mW, so doubling the losses - better to drive from buck converter 3.3 -> 1.8v at 80% efficiency gives only 8mW loss. A suitable microcontroller sinking the 18 LED and driving 5 p-channel high-side mosfets on 3.3v will consume around 20mA on top of the display, or another 66mW (led matrix drivers like MAX7219 consume too much power and are physically too large). So allowing an extra 15% we need around 133mW from 3.3v or 40mA. A 150mAH Li-Ion pouch battery will give 2 - 2.5h of operation in a package around 17mm wide x 53mm high x 15mm deep - using 2mm x 2mm chip LED and mosfets on one side of PCB and everything else on the back.
Its doable - but not for a novice... the uController is a 10mm x 10mm 44pin leadless package on a 6 or 8 layer PCB
You could but you'd need serial-to-parallel conversion on one or both axis; thats at least 3 or 4 x 16pin SOIC chips, which will take far more real estate and power than driving direct from the uController. Also your 16pin PIC will be a SOIC package almost as big as the 44-pin device. There is no way to easily make this small and battery powered and keep it simple, indeed the solution I've suggested is probably the simplest - if you want to manufacture in quantity you have to design for ease of manufacture, and every device you add increases manufacturing and testing costs disproportionally. A nearly two chip solution is by far the most cost effective.Thanks for the analysis. Can't I use a PIC with 16 pins? The pins to be used is just 10 pins. I want the design to be simple.
You're right. I have much to learn. I just don't know where to start from. I need a mentor like you and other experience peopleYou could but you'd need serial-to-parallel conversion on one or both axis; thats at least 3 or 4 x 16pin SOIC chips, which will take far more real estate and power than driving direct from the uController. Also your 16pin PIC will be a SOIC package almost as big as the 44-pin device. There is no way to easily make this small and battery powered and keep it simple, indeed the solution I've suggested is probably the simplest - if you want to manufacture in quantity you have to design for ease of manufacture, and every device you add increases manufacturing and testing costs disproportionally. A nearly two chip solution is by far the most cost effective.
You have much to learn my friend!
Charlieplexed LEDs from uC doesn't need serial to parallel converterYou're right. I have much to learn. I just don't know where to start from. I need a mentor like you and other experience people
True, but charlieplexing is of no use to you - for reasons I will explain shortly - but first lets go back to what you are trying to achieve...Charlieplexed LEDs from uC doesn't need serial to parallel converter
Thanks Irving. I'm trying to use text font that's readable to anyone in english. I want to achieve a 0.5second scroll i.e if an LED is on then in 0.5s the next one should one depending on the character to be displayed. I don't have a peculiar bitmap since I want the use to select any character or words of choiceTrue, but charlieplexing is of no use to you - for reasons I will explain shortly - but first lets go back to what you are trying to achieve...
I realize now of course your proposed display is 5 high and 18 wide, so what font are you planning to use, and how fast will it scroll? Do you have a bitmap representation of the font?
Did you have a specific LED in mind or were you quoting a 'generic' example?
Yes, I get you want the user to specify the words, but you have to say how each character looks... so, for example, is the font based on a 5 x 5 bitmap or a 5 x 4 bitmap? For example, in a 5x5 font the character A is represented by the 5 binary values:Thanks Irving. I'm trying to use text font that's readable to anyone in english. I want to achieve a 0.5second scroll i.e if an LED is on then in 0.5s the next one should one depending on the character to be displayed. I don't have a peculiar bitmap since I want the use to select any character or words of choice
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