Anybody done batteries management before?
I'm working on a wireless handheld controller, still looking for suitable battery solution and charger. Would prefer to build my own charger but it's too risky for this project, maybe next one.

Anybody know where can I get suitable battery & charger at reasonable prices? I need at least 7.2v 2000mAh. Those RC hobby shop mostly don't provide any datasheet, don't know how long they'll last.

Hehe didn't expect any answer from here..

Anyway I've settled on either Li-ion or NiMH battery, Lithium based preferred after reading Battery University. Lot's of good information about batteries there including battery charging graphs.
I'm getting both the battery and charger from Farnell. I can't really trust those from hobbyist shop, only info I found is they are made for high current discharge, 10C, 20C and upwards, while their lifecycle is only like 30 to 50.
My current requirement is much lower, ~300mA peak, average is probably less than 50mA. Battery needs to last at least 8 hours before recharging and I need to make sure the battery can last for at least 1 year of usage.

I'm not building the charging circuit this time, but from what I gather, accurate voltage sensing, and current control is very important to have maximum battery lifetime. I'm not sure why you need the 10A requirement, but a linear voltage regulator with 10A output will be very large (needs lot of heat sink) and inefficient. Building a switching regulator on the other hand is like a project on it's own already (another project I've always wanted to do )

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Added on May 9, 2009, 12:27 pmOh yeah, you'll need temperature monitoring, and maybe separate cell balancing for a really complete charger

This post has been edited by tgrrr: May 9 2009, 12:27 PM

Um.. I don't have the link, but I was searching through foreign website that sells R/C stuffs (looking for datasheet or more information), and I recall they mention the current output capability together with the number of cycles (maybe guaranteed to work?).
Well my opinion is, at 10C to 20C, they are draining a 2000mAh battery at 20A to 40A. That kind of usage might perhaps be the reason of the low number of cycles, which means perhaps moderate usage won't have any issue.

The High Current Regulator Supply is only 2 A. Anyway for ~3A, there are some single regulator choices, LM307 or something like that, in TP03 or T03 package (looks like a big metal transistor with 2 legs, the body is ground). The key with linear regulator is heat dissipation, so with adequate heat sinking, maybe can go up to 5A. And another big consideration is the transformer, it'll be huge to be able to supply 10A. Make sure the secondary winding can sustain 10A of current!

Switching is dangerous, as it plays with high DC voltage, and requires active control by uC. That means feedback isolation is required.

Oh I thought the 10A is for battery charger, so it's to drive some motors, another project?

Hmm.. 8.4v-7.2v to 6v is not much difference. Wait, you sure it goes to 8.4v first? I thought rechargeable batteries output when loaded is pretty much constant, until it's charges fell below certain level, then it dips sharply. I was thinking a simple resistor might be enough. Then again there maybe other things to consider like motor EMF backlash, so using a pass transistor might be better like your high current regulator up there might be a good choice. Reason is, not much voltage drop so low heat dissipation required.

Well I remember I was reading these links some months ago SMPS and this SMPStech. Switching is nice, because can control the output voltage using a uC

Ah don't take everything I said to be correct, I just fired them off the top of my head

8.4v to 6v sounds very simple until you factor in the 10-15A current requirements
But I think that's where the fun is And I might need some advice in motor control from you later on

From the link all you need is a level translator to convert TTL to RS232 signal. You're attempting to use PIC because of some reason or for fun? And even if you use a PIC, you still need a level shifter.

Anyway I think you are trying to use the built-in hardware UART module plus a software UART. The problem is your software UART is non-existence.
Like this piece of code,
while(PIR1bits.RCIF==0);
PORTBbits.RB6=RCREG;

RCREG should contains a full byte of data received from the hardware UART.
You can't just assign them to pin6 of portb like that. You have to send out the individual bits in them one by one, AND watch the timing as you send them out or it'll end up as unreadable junk on the other end.

Level shifter you can simply grab one from jalan pasar or get from farnell, they are pretty common IC. Search for MAX232. This way takes the least amount of effort.
Or as Cerita Dongeng suggested, you can try building one using transistor or other basic component, this will be ok if you're comfortable with electronics.

Note you need a level translator (also called level shifter) EVEN if you have PIC. The reason is the output from your hdd is TTL (0 to 3.3v/5v) whereas the pc com port is RS232 (usually around +9 to -9v). Connecting +9v or -9v to any pin of your hdd is probably going to kill it.
And take note TTL can mean 3.3v or 5v, and they are mostly but not always interchangeable e.g. if your hdd UART is 3.3v tolerant only and you connect it to your PIC that pumps out 5v, something bad can happen.


Whatever you type in HyperTerminal get's send out by pc as a string of bits, and the PIC hardware UART detects the start bit, collects all the data bits, pack them into a byte, place them in the RCREG AND set the flag telling you it's received a byte.
PIC only has one hardware UART. Since you need another UART, you need to handle all of these in the software yourself!

And there are other problems with your code. I just highlighted one of the problem because I think writing software UART is not very easy and I don't know if you can handle it or are willing to try, especially since you don't really need it. But if you still want to try a software UART it's up to you.

Buy online from Farnell, they'll ship to your doorstep. Pay through maybank cash deposit or maybank2u online.
See here -->Max232 @ Farnell

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Added on August 12, 2009, 6:33 pmI think parallel port is all but dead. Why do you want to use parallel port? Do you already have some tools to control the parallel port with?


I don't know if the kind of programmable IC you're looking for exists.
You can make your own simple audio player using micro-controllers like PIC, but you'll need to write the whole program, not just the song you wanted to play.

This post has been edited by tgrrr: Aug 12 2009, 06:33 PM

I can't open the picaxe website. But anyway, those are using PIC controllers. You can achieve the same thing by building your own controller board and writing your own code, provided you know how to do that. I've never tried them but the higher end 16-bit PIC has DSP for advance sound processing.

Or are you looking for a finished product? A quick google search shows this -->Some stuff. Looks like something you're looking for but I've no idea on the cost.

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Added on August 13, 2009, 11:00 amthat really sounds like a FYP.

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Added on August 13, 2009, 12:05 pmOh I didn't know you just want some beeping music. I'm thinking using PIC to generate PWMs at the frequency of music "note" will do the job. Then you just need some driver circuit for the speaker.

This post has been edited by tgrrr: Aug 13 2009, 12:05 PM

There are types of IC. Many have specialized functions like the Max232 converter or some audio encoder/decoder.
Other are basic building blocks to allow the forming of larger circuitry i.e. logic IC or opamps.

PIC is a brand of microcontrollers which in turn is a type of IC.
Microcontrollers contain a tiny cpu (similar but generally much weaker to the one in a pc), and allows user to program it for a variety of tasks.
Thus you'll need some programming knowledge, and some hardware to 'program' it.

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Added on August 14, 2009, 12:16 pmIt would be far more helpful if you guys first list out,
1. Your level of skills and experiences in programming and electronics -> e.g. if you've build a 5vdc power supply before...
2. Your project overall design architecture -> simple but concise descriptions with or without diagrams. Schematics and code snippets if you had one.
3. Your project current general status -> what's working, what's not working yet...
4. What you're stuck with -> Give as much details as possible of what you've tried and the results.

This will save us a lot of time figuring out what's your problem and how to help you.
Note we do expect a significant amount of effort and responsibility from your side.

This post has been edited by tgrrr: Aug 14 2009, 12:16 PM

Hi there,

I think PIC and Atmel are the most popular 8bit MCU worldwide.
Anyway I just started using PIC about 1 year ago when I started doing some freelance jobs and my primary concern then is functionality, availability and pricing which I think PIC did better than Atmel in Malaysia. I've only used the 16F family so far, been wanting to try the 18F family, had couple of those with USB lying around. Now I'm porting my code from assembly to C, using SourceBoost C compiler which seems to be pretty good and surprisingly cheap.

I've no experience or knowledge of ARM. Using ARC600 in my current full-time job but I've really no idea on the different between ARM and ARC. Previous job uses 8051 based MCU and before that in Zilog.


Erm.. what's the reason you wanted to use SMT over through-hole components?
I'm no expert in layout and PCB making, but I think for home-made PCB the minimum track clearance you can create are the main issue, which in turn creates a minimum pcb size you need to make. And making vias for double-sided pcb are very troublesome and unreliable.
Ain't sure about parts availability in Jalan Pasar, but I see from Farnell many SMT are cheaper than their through-hole counterparts.
I'm lazy to build pcb manually too

Aurora, I think ARC is only for custom made IC, they buy the license and embed the ARC core inside their chip together with other stuffs. ARM I'm not sure.

Jalan Pasar is the most popular places in Kl, the whole road there is full of shops selling electric and electronics components.

Penang Island is Hondai (near Sg. Nibong Bus Stations), and Destiny (Near the Bayan Lepas KWSP office).
I know there's a Hondai in Penang Mainland, but ain't sure where is it.

Err.. never tried anything with video yet. How do you interface to the camera? Some high-speed serial or er.. analog AV signal?
I suppose it depends on how much information you're going to stream through your uC and whether your uC can handle it. Sounds like a lot of work I think you'll need a uC with DMA or multiple DMAs to help with the streaming, and maybe DSP for encoding/decoding. First thing I'd check is how much bandwidth is needed i.e. is 1Mbps transfer rate sufficient for your video quality?


Well if your circuitry is not too complex to require using double-sided layout, then yeah.
Else I'd rather use double-sided, the extra dimension can really makes your life much easier.


I think you need a H-bridge. Try google for it. Aurora probably can assist you in this better than me


You should have a circuitry drawn out first. Then you'll be able to tell what components you need. Like the Max232 usually needs some 1uF eCaps to work. And maybe a couple of pull up resistors to your hdd tx/rx line. Plus a vreg to power your max232.

Er, not the Nibong Tebal or something like that in the southern Pg area. Sg. Nibong Bus Station is the only bus station on Pg. Island.
I know there's a Hondai in mainlang Pg., will try to check with my friend.

Well 50x50 line x 1 char (assuming 7x11 size char) == 192500 pixels per image. I'm assuming it's a black&white only image.
Multiply by say 15fps, you'll need to stream through 2887500 pixels per second.
The raw data transfer would be ~360kbps which is sufficient for I2C (usually limited @ 400kbps).
With some encoder chip with good compression, maybe you can achieve higher video quality using the same amount of bandwidth, though I'm just purely guessing about this part and your uC need to decode the data.

Now the question is, are you going to do image processing in your uC, or just stream these data out wirelessly?
Processing data @ 360kbps is a lot of work. You'll probably need some hardware support i.e. some DSP engine.
Wireless transfer @ 400kbps is also rather high.

I haven't been there, but I think this is the location of Hondai Butterworth --> Wikimapia - Hondai Butterworth. The Hondai on Pg Island is correct.

There's tons of circuit on the net. Like this one --> MAX232 Serial level converter. And double check with the datasheet!

Here's the address for HONDAI.

What do you mean by Malaysian site?
The easiest and with widest choices for electronics components would be Farnell and RS online. Both has sales and support office in Malaysia.

Err you can check farnell online on the status of your order, including whether payment has been received, or item has been shipped, or still in transit from it's global warehouses.

So far my experience is those local stuffs will arrive within 5 days, UK stuffs will be next week if you ordered on Monday, and US will take 2 to 3 weeks.
RS is actually faster for local stuff, arrive in 3 days.
Note all these are business days.

And don't order those items that says 'please call'. Those can take up to 3 months to arrive.

If status is "received", I think they haven't confirmed received your payment, and the working days don't start counting until they have payment confirmation.
To speed things up, I usually email my transaction ref # right after making payment.

Last I checked RS online got sell several Li-Ion battery. Not sure about Li-Po.

Or try those Radio Control hobbyist shops. Like this ->RC Battery. Generally RC use larger size battery 7.2v and above, but this shop seems to have a couple of 3.7v choices albeit with smaller current capacity.

Actually I'd advise you to only replace with similar size battery (both voltage and current capacity), and to only get them from reputable sources. I'm somewhat concerned about replacing the battery pack with a smaller or larger unit, as I don't know how your battery charger circuitry works.