I am an information sponge and as I asked the original question - all these responses add value and depth to understanding what I need to achieve.
now if you guys could post some schematicsā¦ 8)
All the more reason to keep those batteries together?
My power specs -
2 batteries ea @ 7.2 V
qty part description
[1] Micro - 5V supply (250 mA draw)
[4] Lynxmotion Rover motors ( how many mA if all in motion/speed?)
[1] SSC-32 - 5V
[1[ Sabretooth motor controller @ 7.2 V
[5] servos from the Lynx 6 arm
[2] cheap servos for my sonars
[2] Max botix sonars 5 V
Near Future power needs
[1] additional Java based micro
[1] RF Data transmitter
[1] RF Video transmitter
What I need is a power header circuit that will allow me to tie in all these devices.
If you guys donāt mind horribly, Iāll make a final post to answer this:
Check out this image, and note the LTC4412 device in the top-middle (E5): geocities.com/saipan59/robots/power.jpg
The LTC4412 is made by Linear Technology. They call it a ālow-loss controllerā. There are likely other gadgets that do the same thing.
The way it works is that E5 āsensesā any attempt for current to go ābackwardsā through the FET (Q7), and turns off Q7 to prevent it.
I would guess that it would work with a bigger MOSFET for more current, but youād have to study the datasheet. The tradeoff is probably that itās response-time becomes longer, but for the type of stuff we do it probably doesnāt matter.
The image shows the power system on my 'bot, although the stuff related to U2 has never been implemented.
Iām not sure whatcha mean about that header board.
The SSC-32 has itās own 5V supply, and if your micro is a BASIC clone, you can get the Mini ABB to supply and breakout it.
Both the SSC-32 have seperate VL and VS inputs.
VL input is intended for 9V batteries.
The battery connected to VL passes through the 5V regulator which suplies all of the ālogicā portion of the board.
The VS header is just a straight-through connection to the battery connected to VS.
This is intended to be a 6V or higher, large capacity battery to power motors and servos.
Thanks for the idea diode circuit! I actually will get a lot of use out of that.
As far as the header thing goes, I think moonbuggie means a board to wire up to the packs and then run the appropriate voltages (regulated or not) to the appropriate boards. This may include some FET switches like in saipanās power supply circuit so he could turn off some devices to conserve power. I can imagine not needing servo control or servos if the arm is stowed properly and the rover is moving around, etc.
My only suggestion is that while the two packs should be more than enough for the motors, with all that equipment, you might need another one, or two. Iām not sure how you want to handle the power board. I donāt think perf. board is really going to cut it, due to the high currents that could involved. I guess it would be possible to drill bigger holes for things like the screw terminals, and use multiple wires to connect components carrying more current, but it would be a pain and not come out looking very nice. If you happen to have access to Eagle (not sure if the trial will cut it for what you want to do) you can design a small PCB and then you can get it fabbed with something like BatchPCB for relatively cheap. Just make sure to make your power traces nice and thick.
As far as regulation, Iām fairly sure that as long as youāre using switching (i.e. FET based) regulators you can put them in parallel. However, the only thing you really need to regulate is your micro board and maybe your motor controller board. The servos can handle a wider voltage range and so can the motors. So you probably wonāt even need to run switching regulators in parallel. This is assuming your charger doesnāt overvolt too much. Basically unless you want FET switches, your power board could just be a few rows of screw terminals, the regulator, and capacitors. Also, assuming you didnāt add more packs, you might also seriously want to consider my diode and cap circuit for the electronics.
I came across the SWADJ simple 3 pin variable switching regulator. It gets nice efficiency too, around 85-90% at 500-1000 mA. The spec sheet is here espritmodel.com/documents/de_parkbec/DE-SWADJ.pdf, this might be of interest to everyone. The downside is that it is very expensive.
I donāt know that I would jump into using this with an R/C receiver without some solid proof of other people using it successfully. It is basically a switch mode UBEC and the long road of battles in getting switch mode regulators NOT to interfere with R/C receivers is a well worn path. Notice in their list of applications they do not list r/c equipment. Iām not saying it wonāt or canāt work, what I am advising is caution in plunking down a wad of cash for this type of item unless there are documented examples of people (other than the people selling them) using them successfully in r/c applications.
edit: I have just confused this project topic with the guy making a 4wd w/pan+tilt and an arm being controlled via r/c where he is already dealing with learning about power routing, ground control, and separation. If you are looking at this for autonomous or hard wired control applications it is probably just fine to use. My concern was in regard to using it in the r/c application I just mentioned. sorry for any confusion I may have introduced.
No problem, your post actually got me thinking I might need to be more careful about using switching regulators with radio controlled projects. I havenāt encountered any problems (I mainly use bluetooth and WiFi as my radio links) but I also am not at the stage where I need any range as all the pieces are either on my workbench or across the room. Any tips on how to plan things so they donāt interfere? I can certainly see how it would be nice if I wasnāt working against myself when I finally did want to give the bot a good long range WiFi link.
actually bluetooth and wlan are packet based with error detection and correction capabilities. noise just reduces their throughput (sp?). typical r/c radios are analog and you only get 50 updates a second so scrambling even 1 frame can cause a perceptible glitch. most wlan access points, certainly your computer and laptop with a wlan or bluetooth card, and non-battery powered bluetooth peripherals are using switchmode power supplies. What you need to do is keep the power clean. It is not uncommon to isolate rf or analog sections power from the main digital power with small r-c or sometimes pi filters. filtering and common mode chokes at the point the power enters the board also help keep the switching crap out of the board to begin with. it is very common in multi-layer pcb designs to carve up and control how the power and ground planes allow current to flow between portions of a design. in 2-layer design you are always trying to balance ladder power distribution against star distribution layout to control how noise moves between circuits. very generally speaking just consider every conductor both an emitter and an antenna, remember that signal strength falls of as the square of the distance, and itās always easier to keep noise out of a system than to remove or deal with it once it is in there.
Thereās the LM2574 .5A simple switcher family that I know of.
The 12V one has been used in many of the OSMC designs, so Iām pretty sure that itās safe to use when dealing with large loads as well as with or close to radios.
Then again, Iām basing that simply upon them repeatedly using it.
Maybe thereās been interference and no oneās noticed.
I actually will get a lot of use out of that.