battery indicator

nos_slived · Post by **nos_slived** » Sun Dec 04, 2005 12:32 pm

I want to open up a gameboy, and see how the low battery indicator works in that.

G-force · Post by **G-force** » Sun Dec 04, 2005 1:01 pm

If you could also make a built-in charger, I might pay even more than $20...

Couldn't you do something like wire up an LED that switches colors when it reaches a lower voltage? (or do they not even make such a thing and I am gonna sound stupid...)

superdeformed · Post by **superdeformed** » Sun Dec 04, 2005 2:39 pm

Sounds like a great idea, but $20 actually sounds a little too cheap. I'm assuming you'll be making the boards yourself, so are you just not considering the cost of the boards and time required to make them, or can you get them made through the school for free? There's also gonna be the cost of the other components: capacitors and resistors (although, the smaller surface mount ones are dirt cheap), the LEDs, and any connectors you decide to put on it. So unless you can get all of the other parts through the school for free too, I think it's gonna cost almost $20 just to make each board. It would definitely be a plus if you could keep it around $20 for the sake of everyone that wants to buy one, but if you are doing this entirely for profit then I think you're gonna be short-changing yourself.

G-force: They do make multi-colored LEDs, even RGB ones, but usually the voltage difference to change the color is pretty steep (over a volt sometimes). You could probably rig something up to make them work, but it wouldn't be anywhere near as accurate as using a microcontroller designed for monitoring batteries.

Post by **Skyone** » Sun Dec 04, 2005 3:46 pm

superdeformed wrote:...but $20 actually sounds a little too cheap.

Shhhhhh.

timmeh87 · Post by **timmeh87** » Sun Dec 04, 2005 4:52 pm

lol. well these chips im looking at are pretty self contained, internal oscillator and everything. I will look into making the boards myself. if i do, i already have enough chemicals for like tonz of boards, and i can get a 6x6 photoresist board for 15 bucks. so i can get 9 2x2 boards out of that, which is like 2 bucks each (profit included)

so lets say i get the chips for 8 bucks (they are cheaper if i order 25 or more! so maybe if i can get 25 preorders....), and make that 11 to include profit. i was planning on designing it with a pin header, and a ribbon cable included, but you gotta solder your own LED's onto the other end of the ribbon cable. that way i can cut costs and make it customizeable. so the ribbon cable/pinheader is like 2 bucks; profit included. then id probably need like 6 resistors, and two caps. ... 4 bucks?

so what am i at?

02
11
02
04
----
19 bucks

and i will probably find more crap i need, and prices might work out differently...

so what we are looking at is like a 25$ device (thats my goal now. keep the price under $25), plus shipping.

there are a lot of features on this that i could make optional... i was thinking it would be cool to include a temp. sensor and a fan driver. the temp sensor is designed to measure the battery pack temperature, but you could probably measure the heatsink temp instead, then get one of the FET driver pins to kick in a cooling fan when it starts to get too hot. it could possibly allow for designs with smaller heatsinks...

Post by **Skyone** » Mon Dec 05, 2005 2:22 am

Don't mean to bug you, but when do you think you would be done with some? No pressure.

timmeh87 · Post by **timmeh87** » Mon Dec 05, 2005 10:40 am

i found a better chip from TI last night. its not as fancy, but its a lot cheaper. i ordered free samples, they should be here by like tomorrow.

i gotta figure out how the chips work, then i gotta design a board, then i gotta do some testing... THEN i gotta send out a few units for other people to test. you can be one of those people

with my '64 busted for the time being, ill have more time to work on this project too.

these chips also have built in charge control. so g-force will be happy.

as far as making one LED change colour, i think we might be stuck with a 5 segment display with these chips. of course, you may be able to figure out how to rewire the various segments to do something you want to do. (im thinking... transistors).. and a green/yellow LED will work fine for the colour chaging. it just has 3 leads coming out of it. one ground, one to turn on the green half, and one to turn on the yellow half.

sydney075 · Post by **sydney075** » Mon Dec 05, 2005 1:34 pm

Well I'm going to keep an eye on this. I was looking into building my own but if you manage to put together them at that price I may just have to get one or more from you.

Extreme_Jesus · Post by **Extreme_Jesus** » Mon Dec 05, 2005 4:20 pm

If you want to di this for a lithium ion or a ni-cd battery you'll need a different system altogether as you'll need to know the current rather than the voltage.

First you'll need to step down the voltage, to do this you can use this circuit

http://img425.imageshack.us/my.php?imag ... it17it.jpg

this will count down the voltage (for this situation im taking 9v down to 6v
The odd looking diode is a special type called a Zener, the resistor value above it depends on the diode you will need the 6v out to power the seconf circuit which will show the status of the battery

http://img36.imageshack.us/my.php?image=circuit44ks.jpg

This is the circuit for showing the status this uses a stadard 741 op-amp chip, in the + you need the power directly from the battery (not the stepped down bit) and then attach the - to the bottom of the first resistor, which takes the 6v (stepped down) in and then through the second and to ground, this means that when the voltage is high (+) the LED is on (output of the 741) and when the voltage is low its off.

http://img510.imageshack.us/img510/8286/circuit36yy.jpg

This is for 3 LEDs so full power = 3 on, all this takes is 2 extra 741 chips and 2 extra resistors, btw the resistor values dont really matter so long as they are ALL EQUAL.

i havent made this circuit but if i get a chance in the next week, which i probably wont seeing as im in the middle of my exams

timmeh87 · Post by **timmeh87** » Mon Dec 05, 2005 5:38 pm

i ordered some chips that measure the capacity by keeping track of all current that goes in and out of the battery. theyre supposed to be accurate to within like 5% and can drive up to 6 LEDs, and are specifically designed for NiMh packs of multiple cells. they also estimate self-discharge based on an internal temperature sensor. as well, they have a charge controller that can be used to safely charge the batterys, and an end of discharge cutoff to prevent over-discharge

also, li-ions and nicd's are easier to measure the capcity based on the voltage... its the NiMh that have a tough voltage curve to predict capacity from. see the one i posted earlier.

and excuse my ignorance... but in your circuit, wouldnt all three LEDs just all always be on... but at different intensities? or am i missing something about the operation of an op-amp? why step the voltage down to 6v... dont LED's run on 3v?

Post by **Skyone** » Mon Dec 05, 2005 6:11 pm

timmeh87 wrote:you can be one of those people

Oh awesome, thanks! Good luck with your 64 anyway!

timmeh87 · Post by **timmeh87** » Tue Dec 06, 2005 12:08 am

i still dont fully understand how these chips work, but im etching a board for one now. lol. its about 1" by 2". i wont have time to mess with anythign till after my thrusday exam though (i have two between now and then).

WARNING! DO NOT TRY TO ETCH CIRCUIT BOARDS AT YOUR COMPUTER LIKE I AM DOING! I AM VERY EXPERIENCED AT BEING STUPID!!!

lol

Extreme_Jesus · Post by **Extreme_Jesus** » Tue Dec 06, 2005 2:23 am

timmeh87 wrote:i still dont fully understand how these chips work, but im etching a board for one now. lol. its about 1" by 2". i wont have time to mess with anythign till after my thrusday exam though (i have two between now and then).

WARNING! DO NOT TRY TO ETCH CIRCUIT BOARDS AT YOUR COMPUTER LIKE I AM DOING! I AM VERY EXPERIENCED AT BEING STUPID!!!

lol

Well im not entirely sure myself but going on my knowledge of electronics it should work, when i have the chance, ill make one and see if it works

If it does work i might make a PCB for it as well, im fairly lucky though my school has got one of the photo-resit board things, mmmmmmm acid....

timmeh87 · Post by **timmeh87** » Tue Dec 06, 2005 12:21 pm

the concern i have is that the Nimh discharge curve is so flat... i dont see how those 3 LEDs will accurately indicate the charge. id expect all three to be on until about 80% discharge, then quickly turn off within 10 minutes of each other. like how battery meters on cd players that are designed for alkaline batteries do.

rawls · Post by **rawls** » Tue Dec 06, 2005 12:49 pm

In my PSNES (which has been done for months, sans case) I used this. I modified it for my particular battery usage, but it works great. Parts are pretty standard and cheap. It uses almost no power and I used a blinking LED, which draws very little current so it doesn't exacerbate the problem of low batteries. From what I chose for my low voltage alarm level, I get about 5-10 minutes of warning before the batteries no longer have enough juice.