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Home / MISC Areas / Cameras Recharging hacks - 1 2 many 4 all adding usb recharging to the CVS/Wolf cams

Recharging hacks - 1 2 many 4 all (modified 0 times) billw Profile A new, appropriately titled thread for ongoing discussions about adding USB charging capabilities to the Ritz/CVS cameras. A recap... Excerpt from Kiram's original post: FYI i was playing with the connector, and i found that pin 4 is able to power up the camera if you apply 3 volts on it (it is connected to the positive pattery terminal) this was probably done so that they could program the camera without putting batteries in it... j_tetazoo's response: Dude! This means that if you put rechargable AA cells in the camera, and, with a properly sized resistor between the +5V from the USB side and this +3V pin on the camera side (and maybe a DC regulator to clamp the voltage at +3V), you'll be able to convert the camera so that it recharges via the USB port! brite_eye sounded in: j_tetazoo may have just described how Radio shack Flatfoto's recharge themselves! Who will be first with a rechargeable drugstore digital? teslafreak lended some expertise: to limit the charging current a 25 ohm resistor should do. to high a value resistor and youll never charge the batteries as to low a value you will overcharge the batteries if left on the usb continually. id evin go with a 10 ohm for starters but thats my story damm ita starting to hail outside arrrrgh An excerpt from my post: I did a bit of searching for a similar hack and found gold here: http://www.felesmagus.com/visor/ Among other things on this page, it details the charging circuit for a Visor using 2 AA rechargeables (the author suggests using alkaline rechargeables, but other rechargeables will work too.) Basically it amounts to a 10 ohm resistor (right on the money teslafreak!) and two 1N914 diodes to bring the +5 volts down to about +3.2 volts. I believe they're all just in series - again, someone with a clue please confirm. Personally, I'd build this right into the transfer cable so it'll work for all your cameras. Lastly, from sailpix: 74 and sunny here... I highly recommend Atlanta! I heartily endorse this line of hacking for these cameras - rechargables would be nice. If I was doing that I'd search for manufacturer's suggested charging circuitry, reverse engineer one of the non "disposable" SMaL cameras, or reverse engineer a USB-powered battery charger. And the RAW decoder is progressing nicely Kiram. 03-26-2005 15:41:39

RE:Recharging hacks - 1 2 many 4 all (modified 0 times) billw Profile Sailpix, I did a bit of research on battery chargers. It seems that if you're willing to recharge the battery slowly (a trickle charge) the charger design can be simple - like our basic current source+resistor design. Each rechargeable battery type can take a small amount of current applied to it even when it's fully charged without harming the cell. Some thoughts about the various types of batteries, and their relevance in this hack: -Alkalines, rechargeable or not, are poor for most digital devices, because voltage goes too far down before all the power is drained. Also, they lose capacity each time you allow them to fully discharge. -NiMH rechargeables are great for digital cams, power profilewise. The current with which you can indefinitely trickle them without harming the cell is lower than NiCads. In fact, they're quite difficult to safely trickle charge, because the difference between the current needed to charge and the trickle-current isn't very great. -High capacity NiCads are also great for digital cams, power profilewise. They're more resistant to overcharging than NiMH, and you can trickle charge them at C/10 indefinitely, though C/5 might be a good compromise for this project. (excerpt from second source listed below... Charge or discharge current is typically expressed as a multiple of the rated capacity (C-rate). For example, a C/10 discharge current for a battery rated at 1 Ah is 1 Ah/10 =100 mA) Sources: http://www.wppltd.demon.co.uk/WPP/Batteries/Charging_Methods/charging_methods.html http://www.houseofbatteries.com/librarydetail.asp?articleid=10 03-26-2005 17:32:08

RE:Recharging hacks - 1 2 many 4 all (modified 0 times) sailpix Profile Excellent! Sounds like after figuring out a circuit that there may also be some recommendations about which batteries work best for this. I'm actually almost more interested in the hacks for the Visor Handspring. I have one of those that I use frequently and having it recharge automatically from the cradle sounds most nifty - if it doesn't bypass being able to use real disposable batteries when I want to. BTW - that's probably something to consider in this hack. Rechargeables are good - but I'd want to retain the ability to throw regular AA's into it if the rechargables die "in the field". Last idea - I think there's a growing set of "Areas which could use further hacking" around these cameras. I have my own niche (RAW decompression) and others have their areas. But, there are some open areas which we could list to give any new hackers some direction:   - Rechargable batteries (yours?)   - Firmware mods (room for several folks)   - Similar cameras (and camcorders)   - RS-232 serial comm. to camera?   - Cable development   - etc... Or, maybe we could have a large list that includes what areas are currently being actively worked on along with the list of open areas/questions/ideas. Seems like a good extension to the FAQ... - sailpix _/) 03-27-2005 12:11:06

RE:Recharging hacks - 1 2 many 4 all (modified 0 times) kiram Profile Ok, Sorry Ive been off the board in a few days, but I am glad you all are excited about building a recharger. let me explain some simple charger types, and i have to agree that the simple current limiting resistor is probably the best idea. Fast charger: this charger will charge the battery for a short time at a high current (high being anywhere from 100ma to 1A) this is usually more complex than a trickle charger because it has to be able to tell when to stop charging the battery when its fully charged.... another option for using this is to just time it. Another reason not to use this type is the usb port is only able to supply a maximum of 500ma per device. so it would be better to not test the current handling of our expensive computers. Trickle charger: this charger will supply anwhere between 15 and 100ma of current to the battery pack, this charger can be left on indefinitly without harming the battery, in fact this is the best way of storing any rechargible battery. for some calculations. i visited my fav design site http://www.epanorama.net/index.php (by the way i would recommend anyone who enjoys hardware hacking to visit here, it has tons of really good info on just about everything electronic) for charger specific info heres the page http://www.epanorama.net/links/psu_battery.html#charger now for some math hopefully everyone knows I = V/R now everyone is using nicad (or nimh) batterys in these devices so a general formula for charging them is 0.1 x (total capacity of the battery) for nicads this is anywhere between 500 and 1000 mAh. so lets just pick somewhere in teh middle such as 700. which gives us a charging current of 70ma. 0.07 of an amp. now to actually figure out the resistor value we need to find the charging voltage of the battery. the per cell charging voltage of a nicad is about 1.5V (remember that nicad batteries have a discharge voltage that starts around 1.2volts) this means we need a resistor to drop the voltage by 2 volts (from the usb power voltage of 5 volts) and transfer about 50-70 mA. if we rearrange the equation we get R = V/I plug in the numbers and remember to convert mA to A. and i get a resistor value of 28ohms. now to calculate the current handleing of the resistor we need to calculate the amount of watts the resistor will dissipate. on this part we would want to be conswervative because the resistor will dissipate more power when the battery is fully discharged. watts = V x A which is 0.14 watts, thus a half watt resistor will do nicely. ok now to hook this all up. connect a resistor between pin 4 and pin 6 of your connector you dont need a diode to prevent the battery from revirse charging through the usb power connector because when ever the connector is plugged in, there is power supply. This charger will charge up the battery overnight. another option is to make another connector with a wallwart on the other end to charge the battery if you dont want to leave the computer on... Good Luck! (I cant wait for the image decoder to be finished) Kiram 03-27-2005 12:16:58

RE:Recharging hacks - 1 2 many 4 all (modified 0 times) billw Profile sailpix, excellent idea about the addition to the FAQ. I'll probably update it soon with that, and also more info on where to find instructions on busters no-firmware-mod method. I have a Tungsten E, and I love the USB charging - especially when I have to do work away from home, since there's one less wall-wart to pack. If the charging circuit is in-cable it definitely won't affect your abilities to use batteries in the field. Worst case, we might just put an off-switch in the cable so you can recharge with regular batteries in-camera. Though, I think that design then begs a charging indicator LED... feature creep? ;) Kiram, interesting. The diodes were meant to actually drop the voltage sufficiently instead of limiting current flow to a particular direction, but if a single resistor will do the job, even better. I won't be able to really work on recharging until I get a new cable built. Realistically it will be at least a couple of weeks. Anybody else planning on working on this? 03-28-2005 09:42:24

RE:Recharging hacks - 1 2 many 4 all (modified 0 times) j_tetazoo Profile Kiram: Your R=V/I=28 Ohms looks right, but 0.14 watts? Isn't peek power more like P=VI=5x0.07=0.35W. Still, that's <0.5 Watts, so you're OK with a 1/2-Watt resistor. Billw: If you want to add an LED to indicate charging, you can't put it in series, since an LED only handles ~20mA, and we're using 70mA to charge the battery. Put it in parallel with the 28 Ohm resistor, with it's own series resistor to limit the current < 20 mA (you'll need to experiment to get a pleasing brightness; I suggest about 330 Ohms as a starting point). The trick is finding a value that's large enough to protect the LED when you plug in a fully-depleted battery, but is small enough so that it stays illuminated once the battery charges and the voltage difference drops to ~2v. It also occurred to me that maybe a power diode inline with the charging resistor isn't a bad idea. We wouldn't want the camera batteries to feed power back into the USB port if your computer happens to shutdown with the camera plugged in. Here's an ASCII-art schematic: 1/4 Watt 330 Ohm LED +---/\/\/---|>|---+ | | +5V o---+---/\/\/---|>|---+---o +3V 28 Ohm 1N4001 1/2 Watt 03-28-2005 15:41:35

RE:Recharging hacks - 1 2 many 4 all (modified 0 times) j_tetazoo Profile Dammit. I still got the power calculation wrong. The current I used for the worst-case scenario was the trickle current. At a 5V drop across the charging resistor, the current is going to be a lot more than 70mA. I should have used: P = VI = V(V/R) = V^2/R = 25/28 ~ 1 Watt. So, a 1/2 Watt resistor is NOT going to cut it! Best to use a 28 Ohm, 1 Watt resistor, just to be on the safe side: 1/4 Watt 330 Ohm LED +---/\/\/---|>|---+ | | +5V o---+---/\/\/---|>|---+---o +3V 28 Ohm 1N4001 1 Watt 03-29-2005 08:06:50

RE:Recharging hacks - 1 2 many 4 all (modified 0 times) teslafreak Profile | Email a one watt resistor is kinda big and to get five volts across it you would have to have two shorted batteries even dead batteries have some voltage left in them and the camera wont evin come on if your batteries are below 1 volt per cell or so so within moments after carging current is applied your voltage should be around 2.5v across the batteries leaving 2.5 volts to deal with minus the .6 volt drop across the diode leaving 1.9 volts to deal with anyway im working on a built in camera charger using the usb port and the acronym kiss means trickle charging is the way to go ill use a 10~27ohm setup and see what works best and ill start with the half watt ones since thats what i have around the shop the only possible problem i can forsee is a condition where you install the batteries in reverse mabye a 1/4 amp fuse or currnt limiter should be used for that but then thats more to stuff in the camera anyway i just thought id throw that out there teslafreak 03-29-2005 10:12:39

RE:Recharging hacks - 1 2 many 4 all (modified 0 times) kiram Profile I dont think you need to worry about putting the batteries in backwards, if you look at the battery door, you can see that when the batteries are put in backwards, one will not make contact with the door, problem solved with a very neat structural design change. Also teslafreak, you are right, if you put any kind of battery in there, it will jump up to over 2 volts in a matter of seconds, so a half watt resistor is fine. I see i forgot to square the voltage in my initial calculation, so yes it will be more like 0.35 watts. Another thing, if you put a diode inline with the resistor to prevent reverse current flow, use a slightly smaller resistor because diodes add about between 0.4-0.7V drop accross each one. Maybe i will get around to putting up my own faq page sometime that will explain this, have pictures etc 03-29-2005 15:28:53

RE:Recharging hacks - 1 2 many 4 all (modified 0 times) Progard Profile I've been following this board for a while now and have successfully gotten pictures off of my original Blue Dakota. This rechargable ability sounds very interesting and I just wanted to say that at least with my original Dakota, 1600 mAh nimh batteries don't seem to have enough power to run the camera. Thanks for all the work you all are doing! 04-01-2005 15:27:34

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