Connector cable SCI -> Raspberry Pi

[hambleturtle]

I'd like to connect a Raspberry Pi to a roomba 530, powering the Pi (5V 700mA) from the roomba and controlling/monitoring the roomba from the Pi.

Are there any off the shelf solutions (or partial solutions)?

I'm thinking I could use a switching UBEC (dc->dc converter used in RC planes etc) to get the 5V power from the Roomba.

I could use USB to connect to the SPI port if anyone can suggest someone who sells SPI->USB cables to UK addresses.

Or I could use the RPi's 3.3v serial pins and a Logic level converter as suggested here
http://forums.adafruit.com/viewtopic.php?f=8&t=31095

I doubt I'm the first person to want 5V power and 3.3V logic from the Roomba (would be useful for arduinos as well as Pis) so any pointers?

[vic7767]

The Roomba provides 5 volts dc to the MCU onboard the robot. Use a voltmeter and locate the 5vdc source. You may be able to use it for power. You can check for 3.3v to 5 v ttl converters on ebay.

[Gordon]

I'd like to connect a Raspberry Pi to a roomba 530, powering the Pi (5V 700mA) from the roomba ...

Sure, Roomba's have their own +5VREG node that is derived from its battery power; but, I'd bet money (not much, of course) that the SMPS (buck converter ckt) that down-converts battery voltage has no where near "700mA" of margin to share with any add-on peripheral. In fact, it is my guess that Roomba's buck converter's maximum current draw is way less than 0.7A. AFAIK, none of us have determined the power output capability of that buck converter.

Are there any off the shelf solutions (or partial solutions)?

There might be on this board, somewhere, but I don't recall what or where.

I'm thinking I could use a switching ... dc->dc converter ... to get the 5V power from the Roomba. ...

You may be able to do that by directly tapping into raw battery voltage and returning current to battery negative, and completely side stepping Roomba's elex.

Don't plan on tapping into the battery voltage appearing on sockets 1 & 2 of the SCI Mini-DIN receptacle -- that power has a 0.25A (fused) limitation.

When making direct connections to battery terminals, keep in mind a couple thoughts: 1) Charge depletion: 0.7A represents about 35% of Roomba's Clean-Mode current, so, if Roomba has all its motors running when your Pi is controlling it the robot's run-time will be reduced. And 2) EMI coupling: Your add-on SMPS down-converter may require added components between it and the battery terminals to attenuate the converter's switching noise enough to not confuse Roomba's controller.

[mfortuna]

IMHO your nest bet is a switcher type supply, they even have them in the 3 pin 7805 pinout:

http://www.murata-ps.com/data/meters/dms-78xxsr.pdf

A little pricey but it will do a great job of converting the roomba battery voltage to 5V DC.

[hambleturtle]

Thanks for the info, from the sound of it my best bet is to tap directly to the battery.
I understand a raspberry Pi requires a supply capable of 700mA x 5V but normally draws much less power especially without peripherals, so hopefully I'll won't be eating too much of the roomba's battery.

mfortuna: the 78xxsr series you linked to looks like it can only handle 500mA which might not be quite enough at startup, but the data sheet has interesting warnings and suggestions about extra capacitors to avoid the EMI issues Gordon mentioned.

Something like http://www.hobbyking.com/hobbyking/stor ... 3A_5v.html should be happy supplying the power but I might want to consider an input capacitor to protect the roomba from it.

[mfortuna]

I did not even notice that. The one I bought from mouser (which I can't find now) a few years ago was rated at 1A. I found the following as well:

http://www.gravitech.us/35v1aswvore.html

[shining]

Don't plan on tapping into the battery voltage appearing on sockets 1 & 2 of the SCI Mini-DIN receptacle -- that power has a 0.25A (fused) limitation.

Hm, isn't pin 1,2 and 6,7 just a direct connection to the Roomba battery?

[Gordon]

Don't plan on tapping into the battery voltage appearing on sockets 1 & 2 of the SCI Mini-DIN receptacle -- that power has a 0.25A (fused) limitation.

Hm, isn't pin 1,2 and 6,7 just a direct connection to the Roomba battery?

No. Sockets 1//2 have a 0.25A, resettable (polymer) fuse between them and the battery's (+) terminal on 4XXX Roombas. On 5XX/6XX Roombas one or more series diodes are between the fuse and VBAT.

On all models, sockets 6//7 have the master current shunt between them and the battery's (-) terminal, but most people can ignore that bit of information.

[crypted]

Have you had any success making something nifty with the Pi and the Roomba? I have a Pi model B sitting around and just received and began repairing a 530... I'm not hardcore techie, but I'd like to see if there's a quick setup going on.

If you have it working, would you be able to provide a tarball of your sdcard OS for the Pi and describe what you've done, what needs to be done, etc?