designing a battery controller and power supply (and general design problems)

[atsch]

I am currently working on a project that involves multiple tiny differential drive robots.

These tiny robots currently consist of

• a small lipo 1s battery
• this cheap china battery charging circuit
• this cheap china boost converter
• an arduino mini
• cheap 433mHz radio recievers
• two small (presumably stepper) motors with drivers (I have not found suitable motors yet, the ones I bough were to big)

I'd like to unify most of this stuff into a single board, customizing and optimizing many things, because the current stack of at least five boards on each other is a really big mess.

I hope for a single board (or maybe two stacked boards connected with headers) solution to be cheaper, easier and all-around better.

There's one issue: while I have do know some high-level electronics stuff (connect a power supply to some stuff, connect an LED or pushbutton, etc), I have never designed actual circuits at a component level before.

I expect I can just copy over the Arduino and the 433mHz reciever from somewhere and the motor drivers are probably just some passive components and a big H-Bridge (or dedicated stepper controller) chip, so the part I think I am going to be having the biggest problems with (and currently really stuck on) is designing the power supply/battery circuit.

I'd like it to do the following:

• charge the battery in circuit (having the charger external isn't feasible because I plan to have a bunch of these, and the battery will likely be soldered on)
• do some decent battery protection
• boost the voltage up to 5v with enough current to drive two small motors
• not spout so much ripple everywhere that my receiver has problems, in case that could be an issue (Could this even be an issue? No clue!)

My first intuition is to find a chip that does all of that, but I can't seem to find any. So I think I will have to build the circuit using two chips. This is where I can't go any further. There are thousands of battery controller circuits, and even more switch-mode regulator chips. I don't know what to do, or where to start. As mentioned, I can't find any examples to go off of, or "How to design a [insert thing I'm working on]" tutorials anywhere.

Is it even feasible that I try this? Will I manage to hand-solder parts at this scale? It certainly looks daunting.

I know I'm not actually asking any specific questions, and that is likely a mistake, but any help on anything I wrote about is greatly appreciated!

[Mosaic]

Hi,
Sounds like you have a plan to make some type of product or custom device for a specific application and want to reduce the plug N play Arduino assembly to a single integrated module as a system.

That requires a several key things including:
1) Understanding of component level electronic design
2) Understanding thermal design issues for power supplies
3) Soldering and PCB making capability.
4) Debugging capability for when things go wrong, which means a few test instruments like a basic logic analyzer or 'scope and decent DMM.

If this is a commercial venture such as creating a product or product kit, well I think it may be a good idea to put a team together rather than try to DIY as there is much to learn.

If this is just a DIY exercise so you can learn skills and enjoy your hobby, I suggest you just start with designing your system in block mode. Starting by developing the specs for your PSU and then developing and building that. With that done move on to the next block, get it working etc etc.

At the end  you will have several working system blocks which you can either connect via jumpers /headers or  do a complete PCB layout  to have the whole thing integrated as a system.

Thus for forum help: specify the PSU you want (expected input supply & output voltage/current and possibly max ripple and max operating temp.)

Then we can help by suggesting circuits or parts etc.

[jeroen79]

How about reversengineering the layout of the off the shelf modules and then putting them on one single board?
Then you would only need to shuffle them around for the best fit and route connecting traces between them.

[atsch]

Hi,
Sounds like you have a plan to make some type of product or custom device for a specific application and want to reduce the plug N play Arduino assembly to a single integrated module as a system.

pretty much.

That requires a several key things including:
1) Understanding of component level electronic design I understand most of the basics, but I don't have much experience
2) Understanding thermal design issues for power supplies Sure, I'd say I have a basic grasp of them
3) Soldering and PCB making capability. I've soldered a bunch (only through-hole so far), I have a basic grasp of PCB design CAD and best practices (i.e. I watched a bunch of tutorials)
4) Debugging capability for when things go wrong, which means a few test instruments like a basic logic analyzer or 'scope and decent DMM. I don't think I'll really need a Logic analyzer on this one, a scope is on my list of things to get. I have a decent Multimeter (and a shitty one).

If this is a commercial venture such as creating a product or product kit, well I think it may be a good idea to put a team together rather than try to DIY as there is much to learn.

If this is just a DIY exercise so you can learn skills and enjoy your hobby, I suggest you just start with designing your system in block mode. Starting by developing the specs for your PSU and then developing and building that. With that done move on to the next block, get it working etc etc.

At the end  you will have several working system blocks which you can either connect via jumpers /headers or  do a complete PCB layout  to have the whole thing integrated as a system.

Yes, this is a private project. Blocks is the way I am currently approaching this thing, with the power block being my biggest concern right now

Thus for forum help: specify the PSU you want (expected input supply & output voltage/current and possibly max ripple and max operating temp.)

Then we can help by suggesting circuits or parts etc.

My current maximum current estimation with a lot of headroom is the following:

• Microcontroller: I have not measured this directly, but the figures I've read online lead me to estimate 30mA
• Bright RGB LED: I need to get higher-power ones than I currently have, so 100mA
• two tiny motors: 200mA
• 433Mhz reciever: 10mA

This would be a total maximum of around 500mA at 5V output.

So the boost converter would have the following specifications:
IN: 3.2V-4.5V
OUT: 5V 500mA

I am unsure about ripple, because I don't how how much it will effect my radio reciever.
Operating temps: nothing special. At 90% efficiency I'll only be dissipating 0.25W, so I don't think thermals is a big issue. However, I do not really have space for any heat sinking beyond using the copper. The robots will only ever be operating at room temperature.

Thanks for your reply, I hope the specifics help![/list]

[atsch]

How about reversengineering the layout of the off the shelf modules and then putting them on one single board?
Then you would only need to shuffle them around for the best fit and route connecting traces between them.

Yes, I could do that, but the thing is, if I'm rolling my own board, I might as well do stuff properly. Currently, while charging, the board gets 5V, which is stepped down to the charging voltage, then stepped up to 5V again and then regulated again by the Arduino. So I'll have to remove and improve some things. I think if I remove everything that is currently unnecessary, I have so little left over that it's probably just faster to design my own.
Also, on the step-up converter board, I don't know what the SOT-23 is, and there is no obvious way to find out.

[Mosaic]

Wel, unless you really want to design the thing....I'd go with this as a tiny piggyback.
Ebay # 351421932376

Ancel