Anything interesting in the post-holiday clearance bins?

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Re: Anything interesting in the post-holiday clearance bins?

Postby b00nafide » May 28th, 2012, 5:49 pm

News from GPS land:

I've got a GPS-500 unit. Happily, the GPS can be powered by 3.3V even with all the other devices sucking power from the SoC. Happily, the data is already at TTL levels, so in theory it can be attached with three wires. But where is RXD for /dev/ttyS0?

The pads on the other side of the board that appear to be intended for /dev/ttyS0 go nowhere and do nothing. There is a promising trace leading from the general area where TXD2 and RXD2 are attached (for /dev/ttyS1, the serial port for the microcontroller, system console and uboot) but I have hesitated to attach live serial data directly to unknown bits of the SoC for testing.

so... requested the serial pinouts for the RT5350F from Ralink - and back to the main problem: wireless.
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Re: Anything interesting in the post-holiday clearance bins?

Postby k-ww » May 28th, 2012, 8:07 pm

Use series resistors 1K - 4.7K when talking to / listening to the pins.
Even if you drive an output pin with an output, the resistors will limit the current to a safe level.
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Re: Anything interesting in the post-holiday clearance bins?

Postby b00nafide » May 29th, 2012, 5:23 pm

k-ww wrote:Use series resistors 1K - 4.7K when talking to / listening to the pins.
Even if you drive an output pin with an output, the resistors will limit the current to a safe level.


Cool, that brings the output down to a more reasonable 0-1.5V or so.

Now, I have to meticulously scrape away soldermask or find methlyene chloride somewhere...
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Re: Anything interesting in the post-holiday clearance bins?

Postby k-ww » May 29th, 2012, 6:14 pm

The resistors are not to reduce the voltage - they are to limit the current flow if you missconnect the wiring and try to drive an output with another output. [What I like to call a "Murphy sacrifice" to the patron saint of miss-connections ;-) one chip stays at high voltage since it's output is ttl rs232 high, the other tries to drive the pin low - short from VCC to GND occurs, while with the series resistors, the current is limited to what the resistor passes if it were connected between VCC & GND. - and I don't know of any chip outputs that can't source/ sink a few milliamperes or less.
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Re: Anything interesting in the post-holiday clearance bins?

Postby b00nafide » May 29th, 2012, 6:52 pm

k-ww wrote:The resistors are not to reduce the voltage - they are to limit the current flow if you missconnect the wiring and try to drive an output with another output. [What I like to call a "Murphy sacrifice" to the patron saint of miss-connections ;-) one chip stays at high voltage since it's output is ttl rs232 high, the other tries to drive the pin low - short from VCC to GND occurs, while with the series resistors, the current is limited to what the resistor passes if it were connected between VCC & GND. - and I don't know of any chip outputs that can't source/ sink a few milliamperes or less.


Ack! Ohm's law and voltmeter interpretation fail! Can I cite Murphy's law for that too? If I had reduced the voltage to 1.5V max using an NPN transistor and resistors the SoC wouldn't have received a HIGH signal. What I was seeing was an averaging of the digital signal - no oscilloscope or tattoo of ohm's law on my forehead over here... yet. Thanks for the clarity.

I think I'll try to remove soldermask from the four promising contacts and see if I can measure any output from the exposed contacts first before attacking with voltage. :)
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Re: Anything interesting in the post-holiday clearance bins?

Postby k-ww » May 30th, 2012, 6:41 am

A qucik and dirty detector for ttl RS232 signals is to use a two leds connected back to back, and resistor - [use a 1K-4.7K resistor]:
connected from VCC to the pin and you will see if the pin pulses low.
connected from GND to the pin and you will see if the pin pulses high.
[verify that the VCC voltage is high enough by connecting it across VCC & GND first [both ways to verify both LEDs work].
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Re: Anything interesting in the post-holiday clearance bins?

Postby Samot » June 1st, 2012, 12:24 pm

My heli has arrived. Could not even fly it yet as I am at work but I couldn't wistand telneting it! ;)
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Re: Anything interesting in the post-holiday clearance bins?

Postby b00nafide » June 1st, 2012, 2:40 pm

Nothing to report as far as /dev/ttyS0 and the GPS but regarding wireless I turned my attention to the STA module instead of the AP module and have had the encouraging result of TX packets in ifconfig. no RX packets yet. the RT5350 apparently has hardware-based antenna diversity... I'll keep at it this weekend.
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Re: Anything interesting in the post-holiday clearance bins?

Postby Samot » June 2nd, 2012, 9:37 am

Do you know how the motors are driven? Is it using I2C for it?

What about using I2C and Ultra sonic range finder to mantain hight?

http://www.robot-electronics.co.uk/htm/srf08tech.shtml

and

http://www.acroname.com/robotics/parts/R145-SRF08.html

I need to learn how to compile and upload binaries to the choper. Is there any documentation for that?

EDIT: I just found Boonafide's post on netcat... I'll give it a try...
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Re: Anything interesting in the post-holiday clearance bins?

Postby b00nafide » June 2nd, 2012, 2:10 pm

Samot wrote:Do you know how the motors are driven? Is it using I2C for it?


The motors are driven over the serial port /dev/ttyS1 by the program ethtty when it starts. ttyS1 is also used for uboot and the system console. As there is a battery-level indicator in the end-user's application, there is bi-directional communication.

Samot wrote:What about using I2C and Ultra sonic range finder to mantain hight?


I2C is supported by the RT5350, however I have not located it's bus yet. Pending the release of pinouts from ralink, we're on our own. Let me know if you locate the bus!

Samot wrote:I need to learn how to compile and upload binaries to the choper. Is there any documentation for that?


Samot, the SoC can run anything compiled for MIPS32R2 or less (and uclibc). My approach at first was to create a cross-compilation environment for mips32 uclibc using crossdev (gentoo linux).

There's info in this thread as well regarding unpacking, modifying, re-packing and flashing a new rootfs if you want to make permanent changes. Making sure you've got access to uboot through /dev/ttyS1 is a good idea first before making such changes.

If you pull the latest Wive-RTNL environment for the Acorp RT-NL series of routers, you will also have the toolchain you need to build binaries, however, it should be noted that wireless needs a lot of work. It should also be noted that if I ever do get it going, I'll have to create an extensive, possibly fraught with legal issues, patch to the (old!) code they have released. Ralink may eventually release an SDK that supports the undocumented RFIC type in use on this platform.

I want to get this flying by the summer and I'm leaning further towards abandoning the closed-source RT5350 platform in favor of the well-supported TL-WR703N if I don't see a single RX packet soon.

Have fun exploring!
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