Arduino Robot: enabling motors while the robot is connected to COM over USB

Projects General Guidance
1

Hi,

I would like to be able to control the motors on the Arduino Robot platform over serial using Python on the host PC. However the motors on the Arduino Robot are intentionally disabled wen the Robot is powered from the USB connection. Is there any way to unlock the motors while the Robot Control Board is connected to a PC?

Thanks!

soe

2

It looks like the check is done in hardware on the Motor Control board. There are logic gates driving MOSFETs to ground the Enable pin (pin 1) of the motor driver. There are two solder jumpers in that circuit (SJ1 and SJ2) so perhaps changing one of those (most likely SJ2 which goes to the same gate as VUSB) will change the behavior. If it is open, close it with a blob of solder. If it is closed, open it by cutting the trace or removing the solder.

3

Hey John,

Thanks for you help. You're correct, I put a solder blob on the jumpers to keep the enable pin high. The motors now work with both the USB and power cable connected.

4

Hey,

we can't find the SJ1. Can someone post a picture?

Thank you!

5

Elektroniag:
we can't find the SJ1. Can someone post a picture?

I could not find any picture of the board on the Internet with enough resolution to read labels. The solder jumpers SJ1 and SJ2 should be near a 14-pin 74HCT123D Quad Schmidt-trigger NAND gate chip (IC7) and be connected to pin 9 and pin 13 of that chip. If you can find the chip you can follow the traces.

6

Hello johnwasser,

Can't find it !
I found a 74HCT132D 14-pin chip and a kind of... solder jumper?
Photos are attached to this post.

Thank you -

WIN_20150208_102049.JPG

WIN_20150208_132300.JPG

7

I mostly see blur. You can probably put a magnifying lens in front of your camera to allow it to focus closer.

8

Hello again,

(EDIT : don't have any lens. Excuse me !)

If you take the power switch on the left, the presumed jumpers are on the upper-left corner, just at the bottom of the USB port.
They are not-labelled two pairs of besides little squares, separated by a half centimeter. -> you see them pointed by an arrow on pictures, and surronded by a circle on two photos.

By downloading the Eagle ref design, I see SJ1 and SJ2 connected to pin 9 and 13.
I saw the MOSFET driving EN pin to GROUND if VUSB is connected.

But I can't find the TI motor driver chip on board, I believe it's in the closed part.

I also found the 74HCT132D chip, that you see on (blur) first photo of my FIRST post on this topic.

Another thing, I'm almost sure it's unpossible, but can I do that... without any solder? Just a very little wire attached by scotch. Can I do it?

Thanks by advance, Shadow (Florian Durand).

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9

(UP because of the active community that make my topic go to the 4th page! :slight_smile: )

10

ShadowCraft66:
I'm almost sure it's unpossible, but can I do that... without any solder? Just a very little wire attached by scotch. Can I do it?

I don't know if you will get a reliable connection but a conductor and tape might work. It won't do any harm if it doesn't work. If you use wire be sure it is bare copper (or tin-plated copper). Enameled copper "magnet wire" has to have the insulation scraped off before it can be used as a jumper.