Wireless project..... am I being to hopeful?

Steve2381

Hello

I am planning to build a multi-channel TX/RX system using a spare Basic stamp+LCD screen I have in the workshop.

I was hoping to use this RS232, 16 channel servo controller :
http://www.active-robots.com/products/motorcon/pololu-16-servo-controller-kit.shtml

The communication between the stamp and the above module was going to be using a pair of these RS232 modules:
http://www.active-robots.com/products/radio-solutions/a-rm001p-details.shtml

Obviously I have some interfacing to do, but does anyone foresee any problems?·· I am thinking it looks a bit too easy to make a 16 channel radio system.

Any input would be great

Many thanks
Steve
·

stamptrol

This should work fine with a bit of work to understand the servo controller's needs..

If you're trying for distance, always underestimate what the radio manufacturer tells you as to range.

For good wireless rules-of-thumb, go on the B & B Electronics site and download the white paper on data communication:· "10 Commandments of Wireless Communication".· www.bb-elec.com

Cheers,

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Tom Sisk

http://www.siskconsult.com


Post Edited (stamptrol) : 6/26/2009 3:19:42 PM GMT

Steve2381

Thanks
Just wondered if these links were stable. I intend to control a complicated radio controlled boat with the system. I know the range is pretty limited, but what are the chances of interference?

Mike Green

The description of the RS232 modules you mentioned is pretty incomplete. They mention that there's an address for the module and there's CRC checking, but no information about what the module does on an error.

With any radio link, you can't assume anything about the reliability of the link. These are unlicensed low power units and are subject to interference from other sources.

You need more information from the vendor. In particular, how is the error checking done? Is there error correction (retries)? How does the module signal that errors have occurred?

You have to design your control system to be fail-safe in the case of link errors.

Steve2381

I plan to have a safety routine for transmission failures. I my look around for a better pair of TX/RX modules with better interfacing options.

The main problem I can forsee is the fact that I will need to read around a dozen pot positions and convert those to servo positions.
RCTIME is just going to be too slow if I want a reasonable response rate from the servos.

I was thinking of driving simple 555 pulse generators and reading them using Pulsin. Would that be quicker?

Mike Green

Using a 555 for each pot may do the trick if you can get the range of pulse widths wide enough. The pulse repetition rate has to be fast enough so that the Stamp can do 16 PULSIN statements in the timeframe needed. You could also use two ADC0838 8 channel ADCs. That has the advantage of providing more resolution and speed. There is plenty of sample code for this device used with a Stamp. and it's cheap ($2.75 from Jameco).

Steve2381

Thanks Mike... never even thought of an ADC.... Doh!
I quickly looked over the PDF file for the IC and just found some Basic code via Google..... I shall have a play

Thanks
Steve

Post Edited (Steve2381) : 6/28/2009 9:10:45 AM GMT