Any success at bit rates > 38k?

RFM12 Wireless module discussion.

Re: Any success at bit rates > 38k?

Postby seaton » Fri Aug 22, 2008 7:48 am

btw just saw that Sparkfun are selling the new nordic modules at $US3.50/ea http://www.sparkfun.com/commerce/produc ... cts_id=690
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Re: Any success at bit rates > 38k?

Postby jkingdon » Sat Aug 23, 2008 3:50 am

Hi Stephen,

Yes, the Microchip modules operate at 2.4 GHz (with a choice of 16 channels if I remember correctly). As well as all the layers of complex function, which I think I mostly managed to turn off, there is a basic difference in design between these units and the RF12s. As the RF12s only have a 2 byte tx buffer you have to stream the packet out. With the zigbee module there is a 127 byte buffer and you can't stream - you have to fill the entire buffer first and then tell the radio to transmit the packet. I think this contributes to the higher latency, as does the bigger minimum packet size, with a 4 byte preamble, 1 byte sync, 2 byte frametype and a sequence number before you get to any data. Still a really neat module though. It will be nice to learn how to use all the features one day instead of turning them all off!

The current camera is a Canon Rebel/XTi. Max sync is supposedly 1/200s, however it clearly syncs just fine at 1/250 and with the flash directly attached is usable at 1/320 (with caveats). They were either being conservative with the 1/200 rating, or marketing factors were at play.

Wish someone would put that nordic chip on a module for, say $10 or less :) (um, in small quantities that is!). Best I have found so far is the older chip

http://www.semiconductorstore.com/cart/ ... oduct=2375

James.
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Re: Any success at bit rates > 38k?

Postby seaton » Mon Sep 08, 2008 4:20 am

I forgot to ask, but have you tried some shielding around the RF module to see if this is affecting the higher datarates?

Stephen....
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Re: Any success at bit rates > 38k?

Postby jkingdon » Mon Sep 08, 2008 4:26 pm

seaton wrote:I forgot to ask, but have you tried some shielding around the RF module to see if this is affecting the higher datarates?



No, I haven't tried that, and I should do. I want to go back and see if I can get that last step of speed out of the system, so I could think about trying some shielding when I do. At the moment I'm having too much fun using the things to want to rip them apart again :)

I have my three Vivitar 285HVs modified to work with the receivers, and a fairly basic mk1 controller with four channels. Obviously time to buy another flash - *grin*. I have plans on a mk2 controller with an LCD and 8 channel support, so I'm going to have to find some cheaper flashes than the 285. I'm tossing up between vivitar 2800s and Adorama's own brand flash:

http://www.adorama.com/FAB.html

They're both down on power compared to a 285, but should be good for hairlights/backgrounds/snooted highlights. Just wish I could get either of them locally.

James.
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Re: Any success at bit rates > 38k?

Postby seaton » Tue Nov 18, 2008 4:39 am

Hey nice unit you posted under the projects! Well done!!!

Did you end up resolving the speed issues?

Stephen
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Re: Any success at bit rates > 38k?

Postby jkingdon » Sun Dec 07, 2008 10:47 pm

Hi Stephen,

No, I never did get around to having another go at that. Never enough hours in the day! I'm hoping to find some time to come back to it, but the todo list just seems to get longer and longer.

James.
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