RoboSavvy Forum

Daughter board for Gumstix-new questions.

2009-07-09T15:52:31+01:00

Hey guys, the experiment is up and running.
However the results are being a little disapointing... Does anyone know the HIGH and LOW voltages for the Ax-12 servos? Our open collector circuit sets the High at 4.66V or 3.66V and Low at 1.5V or 1V, respectively (they are not independent). However, the servos aren't recognized by the CM-5, and we suspect it's because of this values.

Also, our IMU (from huvrobotics) stopped working... it lights the red led at the start but CM-5 doesn't recognize it... I've tried connecting with different wires and in different bus entrances, and still nothing. Any ideas on what to do?

Thanks

Statistics: Posted by clusher — Thu Jul 09, 2009 3:52 pm

Daughter board for Gumstix-new questions.

2009-06-22T22:28:42+01:00

So all i need to do is setting bit 3 of USART Register B to LOW? I'll be trying that tomorrow! Thanks

Statistics: Posted by clusher — Mon Jun 22, 2009 10:28 pm

Daughter board for Gumstix-new questions.

2009-06-20T08:51:18+01:00

If the UART TX is enabled it takes control of the pin. If the UART isn't enabled you're using the pin in GPIO...

Statistics: Posted by StuartL — Sat Jun 20, 2009 8:51 am

Daughter board for Gumstix-new questions.

2009-06-19T23:11:21+01:00

Again, a confusing post... I'm really needing some sleep. I was talking about CM5, therefore only AtMega, not XMega... I can't find how to define if the pin is used as UART or as general purpose.

Statistics: Posted by clusher — Fri Jun 19, 2009 11:11 pm

Daughter board for Gumstix-new questions.

2009-06-18T23:30:42+01:00

The Xmega is more flexible an hence more complex tan the ATMega which I have used.

If you look at the data sheet, then the alternate function (UART) can override the GPIO, so do not enable the UART. Port PE1 is TX out on the ATMega, but not on the XMega, this would be port PE3.

Take regard to the different datasheets for XMega A, XMega128-A1, and the ATMega128

Work only with the I/O port registers. For Port E these are 32 registers located at peripheral address starting 0x0680 (datasheet section 31) and are defined in datasheet section 13.17

Assuming you work with PE1, then you must consider the DIR direction register to set PE1 as output, then use the OUT register to set and clear the bit, or alternatively use the set/clear/toggle.

Consider the setting of the PIN1CTRL for the mode you want to experiment with.

Statistics: Posted by i-Bot — Thu Jun 18, 2009 11:30 pm

Daughter board for Gumstix-new questions.

2009-06-18T21:17:17+01:00

Sorry, I really wrote a confusing post.
You really hit the spot, I'm trying to get it to work as a general purpose pin, but I have no idea how to choose the mode... which register defines this?

Statistics: Posted by clusher — Thu Jun 18, 2009 9:17 pm

Daughter board for Gumstix-new questions.

2009-06-18T15:28:10+01:00

It is not clear how you are trying to use PE1. PE1 can be used as UART TX or as general purpose output. You say your are driving high and low which suggest general purpose, but say you enable TX which suggests UART.

Depending on which it is make sure the configuration registers are then set correct

Statistics: Posted by i-Bot — Thu Jun 18, 2009 3:28 pm

Daughter board for Gumstix-new questions.

2009-06-18T12:46:20+01:00

Hey guys, new question.

So, our professor asked us to make a little experiment in order to measure the rise time using open collectors and not using them. The idea is to measure a rise time from the DATA pin of the AX-12 BUS using an osciloscope.

There I went, making a simple C program that would allow me to manipulate the PE1 pin to HIGH and LOW. The thing is, it doesn't work. I enabled the TxD mode, and then I made a small program to pull the pin HIGH and LOW... It gives a really strange signal... Am I doing it right?

Statistics: Posted by clusher — Thu Jun 18, 2009 12:46 pm

Daughter board for Gumstix-new questions.

2009-06-09T10:38:38+01:00

Also I am not sure if you are making a PC board, package is also a consideration.

Yes, we were looking at DIL packages, not SMD, in order to use sockets to change it if something goes wrong. I don't actually find any not SMD of this max3003.

Anyway, with so many issues it seems to me that once we get a solution we won't bother with the package... But I'll have to confirm it with our professor.

To have one enable per line, I just see IC with only one line and 6 pins each (V_I, V_O, VL, VCC, GND, EN). This requires 12 IC of 6 pins and I think it's a lot of space in our board! :\

Statistics: Posted by ricardocrl — Tue Jun 09, 2009 10:38 am

Daughter board for Gumstix-new questions.

2009-06-09T02:18:02+01:00

This Maxim device looks like it will work, though I think that seperate direction control of each bus would be better, and maybe easier on the software.

From a cost perspective the Maxim device is more expensive, though in very small quantity (< 4) is lowest cost due to the Maxim generous and responsive samples policy.

Also I am not sure if you are making a PC board, package is also a consideration.

Statistics: Posted by i-Bot — Tue Jun 09, 2009 2:18 am

Daughter board for Gumstix-new questions.

2009-06-09T01:03:55+01:00

Hi guys,

I am the partner of clusher. I'm a student with not much knowledge trying to help in this project. I'm really newbie in all this matters, microprocessors, electronics, and so on. So... go slow if possible when explaining things.

In order to solve this incompatibility of power supply (3.6v -> 5v) we thought of Logic Level Translator from Maxim. I saw this one: MAX3003 - http://datasheets.maxim-ic.com/en/ds/MA ... AX3012.pdf. It has an enable pin (EN A/B) to switch from active mode of A lines(I/O) to B lines, having 4 of each. What about using this, just choosing to receive or to transfer data (all buses at the same time)? A's receiving and B's transfering, for example.

I think this would solve: the different logic level problem, the enables inverted for receiving/transferring, reduces the I/O pins to control and uses few components in the board.

Statistics: Posted by ricardocrl — Tue Jun 09, 2009 1:03 am

Daughter board for Gumstix-new questions.

2009-06-09T01:00:33+01:00

I have not used the XMega, and was surprised that the I/O are not 5V tolerant. I am using the AVR32 and they are.

The AX12 use HC logic, so do need 5V CMOS levels

I suggest to still avoid open collector if possible at these data rates on servo wires.

How about to use different devices for Transmit and receive. For transmit you need a 5V CMOS logic family with TTL compatible inputs. These will take input from 3.3V logic OK. This should be powered from 5V. Like a 74HCT126.

For receive use a 3.3V CMOS logic family with 5V tolerant inputs, like the 74LVC126. Power this from 3.3V

Statistics: Posted by i-Bot — Tue Jun 09, 2009 1:00 am

Daughter board for Gumstix-new questions.

2009-06-08T16:56:25+01:00

@i-bot: I just wasn´t sure if the XCK bit could be software controled. We are looking at open colector because the AtxMega uses 3.3V and the AX-12 only recognizes HIGH at 5V. This means that if we use the tristate buffers, we also have to convert from 3.3V logic to 5V... with open collector this would not be a problem. However, we still need to see if we can maintain 1Mbps communications with open collector, because if not then weare back at directional bit!

@limor: we are using the gumstix verdex (you know... the IST group at Portugal). We are using 6UARTs to communicate with the servos and 1 UART for the GumStix. I don't have the most recent designs, I'll ask to my partner. We are expecting to be able to compress the Dynamixel enough to make this efficient. Plus, the Bioloid now has the 6Axis IMU from huvrobotics (I'm considering reserving one bus for it alone) and there are plans to make contact or pressure sensors for the feet.
The general idea would be to distribute the buses as 1.IMU 2 and 3. Arms 4. Hip zone 5 and 6. Legs

Statistics: Posted by clusher — Mon Jun 08, 2009 4:56 pm

Daughter board for Gumstix-new questions.

2009-06-08T16:53:39+01:00

If you want to share the schematics either public or private, I can check them and help you with the hardware configuration.

Statistics: Posted by i-Bot — Mon Jun 08, 2009 4:53 pm

Daughter board for Gumstix-new questions.

2009-06-08T16:37:28+01:00

Hi clusher

which gumstix version are you looking at?

i'm always on the lookout for anything that will help get better closed-loop-control for the bioloid bus. what i like about the the Xmega series and their many UARTs is the potential to split the Bioloid bus into several independent portions. sub-bus gets fewer servos allowing send-receive packet cycles of 150/sec instead of <50.

so if closed loop control is what you are after, then i would recommend using 5 of 6 UARTs to control 5 independent Bioloid buses and 1 UART to communicate with the Gumstix. The Dynamixel protocol is inneficient enough that 5 UARTs running the 1mbps Dynamixel protocol can probably be compressed (for the purpose of closed loop control) into a single 900kbps talking to the gumstix.

any chance you can post the schematics ?

Statistics: Posted by limor — Mon Jun 08, 2009 4:37 pm