Go Down

Topic: 3 motors on an arduino????? (Read 2 times) previous topic - next topic

dc42

#5
Nov 27, 2012, 01:28 pm Last Edit: Nov 27, 2012, 01:32 pm by dc42 Reason: 1
Yes. To control each bridge you need only the DIR and PWM pins, so that's 2 pins per motor, 6 in total. If you want to set the current limit then you need the SPI pins as well (you may need them anyway to configure the device the way you want it), but the controllers can be daisy chained (see http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00268302.pdf). So that's 4 shared pins. If you also want to power all 3 down, you will need one more output pin to drive either the EN inputs or the DI inputs. Total 3 PWM pins and 7 normal outputs (8 if you want to power the drivers down to save battery). You still have 9 or 10 pins left, also 3 of the SPI pins can be shared with other SPI devices.

BTW I've never used that board so I can't vouch for its quality, however the chip it is built around looks very nice.

[EDIT: by "enough room" I assumed you meant "enough output pins". These are not shields so they do not plug directly on top of a Uno.]
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

amp625

yeah i did mean pins, that clear up a lot thanks. also do you know how many amps those bridges can support per motor?  it wasnt on the description

dc42

The chip (see datasheet I linked to before) has built-in current limiting which you can set (by SPI) to set 4 different current limits: 2.5A, 4A, 6.6A and 8.6A. At the higher end of that range you would probably need a fan to keep the heatsink cool.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

amp625

#8
Nov 27, 2012, 05:05 pm Last Edit: Nov 27, 2012, 05:18 pm by amp625 Reason: 1
But the link on ebay isnt a L9958 (the data sheet you sent me), and how do you daisy chain?  Does all the stuff from the data sheet apply to that bridge?  Thanks for all your time.  Also can you run brushless motors on it?

dc42

Good point. The eBay page says the unit is a SX8847. When I googled "SX8847 datasheet", the first match was the L9958 datasheet I linked to. I don't know why, I can't find any mention of SX8847 in the datasheet.

However, the description of the I/O interface on the eBay page matches the description in the datasheet, so does the block diagram. Also, another item I found on eBay that appears to be a rather similar board has a L9958 chip in the photo, see http://www.ebay.co.uk/itm/Arduino-240W-High-power-H-Bridge-Motor-Driver-Module-Smart-Car-Driver-/330817755465?pt=LH_DefaultDomain_0&hash=item4d06465949.

So I think it very likely that the unit I linked to is based on the L9958.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

Go Up