Robot power supply

Rsadeika

I dug out my old iRobot Create and I started to play around with it. Now, the question or problem I have too deal with is the power supply issues, or possible issues down the road. My set up at the moment is, I am getting a power source from the Create robot ~18V @ 1.5A, and I am using a PropBOE board, it seems like the PropBOE board is not getting hot, but I will be adding other boards and devices, and they will be drawing the regulated power from the PropBOE. I already tried adding a Raspberry Pi 5v @ 1.5A, and the PropBOE still does not seem to be getting hot. I suppose that at some point the PropBOE will shutdown when it reaches a specific amp limit, but not sure how calculate for something like that.

I guess the best solution would be to have a power supply that would tap off of the Create battery, and then have the boards pick up the necessary voltage. Since most of the Parallax boards that I have are using a barrel device with a required 6-12V and the Raspberry Pi has a pin(s) or a mini-USB for attachment, I am not having much luck finding such a power supply too meet my needs. So, the question is, does anybody have a source for this, I already tried the usual suspects - Parallax, Futurlec, Sparkfun, Adafruit.

Thanks

Ray

kwinn

You can probably continue to power the boe board, RPi, and a limited number of other boards from the 18V supply. The boe board LM3478 power supply controller is rated for 40V in, and the switching transistor (Q1) for 30V so you are probably fine as far as that goes even though the data sheet specifies a 4-16V range. At typical efficiencies the switching regulator on the boe should draw about an amp from an 18V supply when putting out 3A at 5V

Output current spec for the 5V is up to 3A, although I would be reluctant to run it continuously at that current. The boe board itself can run from the USB connector so it cannot be drawing more than 1/2A, which leaves a maximum of 2.5A you could use from the boe's 5V power supply.

Rsadeika

Thanks kwinn. I looked at the schematics and docs for the PropBOE, and could not make any sense of it, I am not a hardware guy, not too that detail anyway. Now, I changed my opinion of the PropBOE, it is a GREAT little board, since I can now use it as the main access board for my robot project.

Since I plan to use C as the preferred language, for my robot project, I was hoping that the Activity board had the same voltage regulation setup as the PropBOE. Why, because the Activity board has all C drivers, and the PropBOE has all Spin drivers. So, it will limit some of the expansion that I will be able too accomplish using the PropBOE board, unless I want want too make heavy use of spin2cpp.

I am still interested in finding a variable power supply that would fill the previously stated needs. That way I could give power to all boards without worrying about any amperage limits, and seeing a complete power shutdown when the limits are accidentally hit. You would think that Parallax would have a product like that available, after all they do sell robots that use batteries and control boards.

Ray

kwinn

Rsadeika wrote: »

.....

Since I plan to use C as the preferred language, for my robot project, I was hoping that the Activity board had the same voltage regulation setup as the PropBOE. Why, because the Activity board has all C drivers, and the PropBOE has all Spin drivers. So, it will limit some of the expansion that I will be able too accomplish using the PropBOE board, unless I want want too make heavy use of spin2cpp.

I am still interested in finding a variable power supply that would fill the previously stated needs. That way I could give power to all boards without worrying about any amperage limits, and seeing a complete power shutdown when the limits are accidentally hit. You would think that Parallax would have a product like that available, after all they do sell robots that use batteries and control boards.

Ray

There are always limits to how much current you can draw from any power supply, particularly when running from batteries, so current draw has to be taken into account.

I'm guessing that you want to use the iRobot as your robot chassis. If that is the case I would suggest buying one of the many available 5V switching regulators and use that to power the boards. Just make sure to select one that has a Vin of 18V or more. Variable output voltage regulators are harder to find and usually more expensive. Most add on boards seem to require 5V, and have on board regulators for any 3.3V parts.If you have add on boards that only need 3.3V I would suggest a separate 3.3V switcher for them.

The boe and activity board seem to have a lot of the same hardware in common, and seem to use a lot of the same pins.

The main differences I see are:

VGA, on boe, not on activity
Power, switcher on boe, linear on activity

I would guess that a lot of the drivers in C and Spin would run on either board, and at most would only require minor changes.