USB Design Idea & Thoughts

[NDO News]

Hi All - would appreciate any thought or pointers on the following.

As a part of a project I am thinking to use a number of USB WLAN adapters,
these would not be used as normal, instead they would plug in to my own
little PIC processor board. the idea is a little PIC chip would communicate
with the USB WLAN device, set its parameters and enable it to go on air -
now these devices would all be visible on a main PC with a WLAN card. the
devices would be used for example with a little temperature sensor and would
send back the data to the PC or in some cases with different devices have a
two way communication.

Now I have heard and read some about the Host Controller for the USB
however, I don't see why my little USB and WAN and PIC device needs a Host
Controller as long as the PIC sets up the registers in the USB device and
initialize it to send and receive the data.

If I am on the wrong track, would appreciate some thoughts and feedback on
this.

Thanks very much.
Sean

 

[James Meyer]

Now I have heard and read some about the Host Controller for the USB
however, I don't see why my little USB and WAN and PIC device needs a Host
Controller as long as the PIC sets up the registers in the USB device and
initialize it to send and receive the data.

Start simply. Getting a PIC to recognize, much less talk to, a USB
device of any sort is a first step in the right direction but one that will
probably take you a year or two to get working.

A PIC to PCMCIA card interface might be an easier project. You can get
PCMCIA WAN cards that work the same way a USB WAN device does.

Jim

 

[Wouter van Ooijen]

Now I have heard and read some about the Host Controller for the USB

however, I don't see why my little USB and WAN and PIC device needs a Host
Controller as long as the PIC sets up the registers in the USB device and
initialize it to send and receive the data.

But *how* would your PIC do that? The only interface you have is the
USB interface, and to use that you must act as an USB host.


Wouter van Ooijen

-- ------------------------------------
http://www.voti.nl
Webshop for PICs and other electronics
http://www.voti.nl/hvu
Teacher electronics and informatics

 

[Blue News]

I appreciate that, but why would it be so difficult to do this? excuse my
ignorance, but USB uses a protocol, a hand shake can that not be done by a
processor - handshake, initialize the IP, SSID etc and read/write data?

The processor just have to do that, then receive data and send data to a PC
via the WLAN.

The choice will have to be USB only, can not use other interfaces.can some
one break down the USB Host Controllers function briefly please?

Thanks
Sean

 

[James Meyer]

I appreciate that, but why would it be so difficult to do this? excuse my
ignorance, but USB uses a protocol, a hand shake can that not be done by a
processor - handshake, initialize the IP, SSID etc and read/write data?

The processor just have to do that, then receive data and send data to a PC
via the WLAN.

The choice will have to be USB only, can not use other interfaces.can some
one break down the USB Host Controllers function briefly please?

Thanks
Sean

Take a look at http://info.hobbyengineering.com/specs/USBMOD3.pdf to see
what you must build and put between your PIC and any USB device that you want to
use.

You cannot simply connect a USB device directly to some of the PICs pins
and expect anything good to happen.

If you MUST have a USB interface then you MUST use at least all the
hardware that is shown in that user's manual.

You should go ahead and buy something like that module rather than
trying to build your own.

Jim

 

[NDO News]

Thanks Jim,

I wasn't planning to connect USB pins directly to a PIC, I was thinking more
in the lines of one of the FTDI's USB UART devices, these would take USB and
output the data in serial and I am sure have seen a circuit using this chip
outputting in parallel format see link
http://www.ftdichip.com/FTProducts.htm#FT232BM.

Now if I can read/write data from/to the USB WLAN module then I should be
able to initialize etc don't you think?

I don't know of anything (WLAN module) available out there that I can buy to
for example connect a temperature sensor to it and read it on a wireless
laptop...
Have a look at the nasty ASCII block below. This is a design idea I am
thinking about and the criteria is: must use USB due availability of cheap
modules out there - must use existing WLAN as half of the job is done and
for its purpose it needs to use it. these two can not be changed -
impossible?


ANT USB WLAN PIC/FTDI Sensor
Wireless Laptop
|______-----------_____------------____S
----------- ------------
Sean

 

[James Meyer]

Thanks Jim,

I wasn't planning to connect USB pins directly to a PIC, I was thinking more
in the lines of one of the FTDI's USB UART devices, these would take USB and
output the data in serial and I am sure have seen a circuit using this chip
outputting in parallel format

I don't know of anything (WLAN module) available out there that I can buy to
for example connect a temperature sensor to it and read it on a wireless
laptop...

OK, now I think I get a bit better idea of what you want to do.

If you had two wireless laptops, you could connect a temperature sensor
to one of them and read the temperature on the other one. What you want to do
is to replace the laptop, the one with the temperature sensor, with a USB WLAN
device connected to something that can perform the same function as a laptop but
is less expensive.

That "something" might be a PIC but it's my guess that the software and
extra hardware necessary to do the job with a PIC would make it a formidable
project.

A Rabbit microprocessor single-board computer with a built-in USB port
and software support for networking applications would be a much more managable
platform.

Check out http://www.rabbitsemiconductor.com/products/kits/ and AN-405
at that site.

Jim

 

[Wouter van Ooijen]

I appreciate that, but why would it be so difficult to do this? excuse my

ignorance, but USB uses a protocol, a hand shake can that not be done by a
processor - handshake, initialize the IP, SSID etc and read/write data?

If you are ignorant (your word) why do you assume it will be simple
while people who claim to be less ignorant say it's not?

If you want to find out for yourself: start reading the USB
specification.


Wouter van Ooijen

-- ------------------------------------
http://www.voti.nl
Webshop for PICs and other electronics
http://www.voti.nl/hvu
Teacher electronics and informatics

 

[Wouter van Ooijen]

I wasn't planning to connect USB pins directly to a PIC, I was thinking more

in the lines of one of the FTDI's USB UART devices,

These are USB *slave* chips, you can't connect two slaves and expect
something usefull to happen.


Wouter van Ooijen

-- ------------------------------------
http://www.voti.nl
Webshop for PICs and other electronics
http://www.voti.nl/hvu
Teacher electronics and informatics

 

[Reg Edwards]

Slaves are obliged to do exactly what their masters tell them to do.

That is the Law.

 

[Roger Hamlett]

Thanks Jim,

I wasn't planning to connect USB pins directly to a PIC, I was thinking
more in the lines of one of the FTDI's USB UART devices, these would
take USB and output the data in serial and I am sure have seen a circuit
using this chip outputting in parallel format see link
http://www.ftdichip.com/FTProducts.htm#FT232BM.

Now if I can read/write data from/to the USB WLAN module then I should
be able to initialize etc don't you think?

I don't know of anything (WLAN module) available out there that I can
buy to for example connect a temperature sensor to it and read it on a
wireless laptop...
Have a look at the nasty ASCII block below. This is a design idea I am
thinking about and the criteria is: must use USB due availability of
cheap modules out there - must use existing WLAN as half of the job is
done and for its purpose it needs to use it. these two can not be
changed - impossible?

Key thing to understand, is that USB was designed for the _slave_ to be
pretty easy to do. Unfortunately, one of the costs of this, is that the
master has to do all the work. A master unit, potentially must support two
data rates, it has to support polling the devices at defined intervals,
and responding if they require service. It also is required to support
64bytes of hardware buffer. At the very simplest level, what you want,
_could_ be done by a PIC, linked to a FPGA, to handle the interface, with
an implementation of a simplified USB stack, and a single handler coded
for the one target device. I'd be talking in terms of perhaps a couple of
thousand dollars to develop the hardware, and perhaps four times this for
the code, _provided_ the manufacturers of the WLAN module are prepared to
give you full details of how to program the unit. Without this, the costs
escalate.
Conversely, you could attach a 8019 Ethernet controller to a PIC, and talk
to this, with your own RS485 interface, using largely off the shelf code
(there are TCP/IP implementations for the PIC and this chip), and a
prototype, would only involve a very few hundred dollars of work.
The cheapest solution to do what you describe, assuming the device you
want to talk to is supported in Linux, is one of the single board PC's,
with a complete embedded Linux.
As for a Wlan module, there are complete solutions designed to interface
to instruments on the market, that will connect directly to a processor.
Have a look at the Lantronix site, and their WiPort device, or the
Digi-Connect 'Wi-Me'.
What you describe, really is a hard solution.

Best Wishes

 

[Charles Edmondson]

Thanks Jim,

I wasn't planning to connect USB pins directly to a PIC, I was thinking more
in the lines of one of the FTDI's USB UART devices, these would take USB and
output the data in serial and I am sure have seen a circuit using this chip
outputting in parallel format see link
http://www.ftdichip.com/FTProducts.htm#FT232BM.

Now if I can read/write data from/to the USB WLAN module then I should be
able to initialize etc don't you think?

I don't know of anything (WLAN module) available out there that I can buy to
for example connect a temperature sensor to it and read it on a wireless
laptop...
Have a look at the nasty ASCII block below. This is a design idea I am
thinking about and the criteria is: must use USB due availability of cheap
modules out there - must use existing WLAN as half of the job is done and
for its purpose it needs to use it. these two can not be changed -
impossible?


ANT USB WLAN PIC/FTDI Sensor
Wireless Laptop
|______-----------_____------------____S
----------- ------------
Sean

Actually, rather than go through all the USB interfacing to get to the
WLAN, you could use and Airborne from DPAC and just use a serial port.
to interface your sensor system. Biggest problem is the cost of the
development kit.

 

[Blue News]

James,

I have a few of these modules and the idea was to use these for my
prototypes, i.e. PIC talks to one of these modules and the module talks to
the WLAN (USB) - that was the idea, but now I am confused - from the trail
of these posts I thought it can not be done without a USB controller on my
design.

Sean

 

[Blue News]

Thank you for taking the time and your positive inputs. I will be looking at
some of the suggestions you have been making.

Sean

 

[Blue News]

This is a newsgroup where people exchange and bounce ideas in a positive
way. I know it is a difficult project maybe impossible, but if every one
took the same negative attitude as I see in your posts then we wouldn't be
where we are with technology today. There are always ways, work around and
new ideas, look at the few who have bothered to reply to my post in a
informative and positive manner - take Roger or James' post - its not a
negative two liner like "But *how* would your PIC do that?" (your own words)
I wasn't looking for the newsgroup police Wouter. The moral of the story is
if you cant do something positive, don't bother doing it at all.

Sean

 

[Blue News]

Lets look at this from another angle - the reason it needs to be USB is
because WLAN USB are many and cheap. In my project I need to setup many of
these monitoring different things both analogue and digital. I opened on of
these USB WLANs and inside there are Zydas chipsets, are there any way to
bypass the USB section of these little units and tap directly (again broadly
spoken via PIC etc) to the chipset...?
Just a though.