Bidirectional wireless

kelvin james

Was wondering if anyone here has set up a system that uses 2 stamps talking to each other with transceivers? I am looking at some that run at 9600 data transfer, and was wondering if it is a true serial data rate? Is the data instantaneous or is there some delay in transmission time? Have never used any wireless before and am concerned that this could be a potential problem. Any help would be appreciated. kelvin

Ken Gracey

Kelvin,

Many times have we set up wireless Stamp "networks". I use the term loosely, though. Here is one of my projects using our stripped-down, no-frills RF modules:
http://www.parallax.com/html_pages/resources/catapps/cat_toddance.asp

But without a question our Embedded Blue devices are most popular:
http://www.parallax.com/detail.asp?product_id=30068

The Embedded Blue devices, and the SureLink modules http://www.parallax.com/detail.asp?product_id=30065 both provide built-in error correction and accept simple SERIN/SEROUT data.

As for the delay in transmission time, my experiences are quick. . .how's that for descriptive. There is some delay for error correcting/encoding by the modules. How much I don't know.

If it is important to know, I can ask our Tech Support guys to set up the two modules we offer (Embedded Blue / Surelink) on a scope and do a timing test for you. Just give me the command "do it". We could use the data for our web page if it helps you make a decision.

Sincerely,

Ken Gracey
Parallax, Inc.

kelvin james

Well Ken, i feel honoured that you would do a test like that for me, and if you think it would be useful info to post on the site, then that would be pretty cool. On the other hand, if you say it works good, then that is proof enough for me. I was looking to send out continuous pulses at around 50-100 ms, and was concerned that it could handle that kind of data transmission.
BTW , the robot dance project was pretty amazing, i am impressed.
Do you think the transceivers would be reliable within a 50 yard range? line of sight.
kelvin

Ken Gracey

Kelvin,

I have asked our Tech Support team to put together some tests on data transmission using the two RF modules we recommend. We will have this by Wednesday and I will post it on this thread. We will be looking for the delay between transmit/receive.

When you mention that you want to send "pulses" I am pretty sure that with both modules you can only send serial data. Therefore, you will turn the pulse into a one or two-byte value and use SEROUT on the RF module pin (not PULSOUT). Is this okay?

50 yards is no problem for either of the modules. In fact, I have walked out of our office and across the parking lot with a laptop connected to the Surelink modules (sending an image to another laptop inside the office). This was about 100 yards and it worked well.

Thanks,

Ken Gracey
Parallax, Inc.

Stephen Swanson (Parallax)

kelvin,
For the EB500 this is how it breaks down there is a 6 byte buffer in the unit that can reply in 1 ms per byte. If the Buffer is full the time between the next data is 11 ms.





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Stephen Swanson
Technical Support
Parallax, Inc.
sswanson@parallax.com


Post Edited (sswanson) : 11/8/2004 8:53:49 PM GMT

kelvin james

thanks guys, i will have to do some reading and make a sample program to see how i would try and implement this into what i am trying to do. got myself confused a bit, the pulses i want to send are 70-100 us, not ms. , which looks like trouble according to the transmission data rate. just trying to put the whole sequence together on paper, to see if it will be fast enough. never worked with any wireless before, so a new learning curve is on the horizon.
thanks again

kelvin

Bruce Bates

Kelvin -

If you tell us a bit more about what you're actually trying to do, you may get much better responses than you have so far. There are some real creative people on the forum, who'd be happy to help if they have adequate information.

Regards,

Bruce Bates

kelvin james

Yes, you are right Bruce, guess i've been living in "secret mode" since i started this, and time to shed the paranoia about giving anything away. I'll lighten up a bit.
Here's the process---- Motor controller is set to remote mode, meaning direction and movement on the stepper is being pulsed from the pins on the stamp. The encoder is sending the pulses via a pulsin to the stamp and pulsout to the controller. The optimum frequency for the pulsout is in the range of about 70 to maybe 200 us per pulse. The motor runs smooth and very responsive at this rate when the encoder is turned. The stepper motor is mimicking the movement of the encoder. And with an encoder, there are 2 pulses with every step the motor takes, as the direction is determined from that. So, there is a lot happening when the encoder is turned.Works great as a wired setup. THe encoder is just like a real time remote control of the stepper motor.
So, in order to make this wireless, i need to transmit those pulses out to the motor control pins, either through another stamp or directly to the controller. If there is any delay in the transmission, the motor will stutter, or will only be able to be used at a slow speed.
And the way it is set now, the speed of movement is totally variable, from as slow or as fast as the encoder can be turned, which is part of the overall design.
Dont know if i am giving enough info here, but this is the basic operation i am dealing with.

kelvin

Bruce Bates

Kelvin -

I mention the following since you may not be aware that they even exist. There are RF-capable shaft encoders on the market which are used to do exactly what you are trying to do. The RF capabilty is built right into the encoder collar itself. They may be overkill for your project however, due to their high cost.

Although I've never implemented it, you might consider a BlueTooth type of solution.

Regards,

Bruce Bates