Author Topic: Need a low latency wireless transceiver.  (Read 5121 times)

0 Members and 1 Guest are viewing this topic.

Offline vikisonline

  • Contributor
  • Posts: 5
Need a low latency wireless transceiver.
« on: May 18, 2013, 07:34:30 pm »
I am working on a project that needs a very low latency signal to be transmitted wirelessly.
I asked on other forums, I know I can buy these, but I want to make one.

One example usage would be:
A wireless flash controller that takes a signal from a cameras hotshoe adapter, sends a wireless signal to
a flash device, or something that drops, shoots an object.

Timing of course is critical. So the requirements:
-A signal must be fully sent and received withing 1/500 of a second at least, faster is better of course
-Have at least a 50-100m range
-One master must be able to individually talk to on of at least 15 units and broadcast a message to all (at least 15) units at once one data packet
-should be small, relatively low power (batteries) and relatively cheap.

So far I have looked at:
-wifi: possible collisions and congestion issues, tcp packet processing can be intensive for slow microcontrollers, etc etc.
-bluetooth: constantly frequency hopping so not sure if the latency would be reliable
-zigbee: looks promising but want to know if there is anything better/best, and not sure if its capable of broadcast messages.
-nRF24L01P: also nice, cheap ($2.5 from china) but can at most have 6 slaves for one master.

Between price size and latency, latency and size is the most important.

And of course I should be able to control this with an avr/pi/etc... I can write the libraries myself, that in itself is not an issue.

Thanks
 

Offline Simon

  • Global Moderator
  • *****
  • Posts: 13831
  • Country: gb
  • Did that just blow up? No? might work after all !!
    • Simon's Electronics
Re: Need a low latency wireless transceiver.
« Reply #1 on: May 18, 2013, 07:38:47 pm »
you might want to give more details like what is the use so people can better help
https://www.simonselectronics.co.uk/shop
Varied stock of test instruments and components including EEVblog gear and Wurth Elektronik Books.
Also, if you want to get ripped off: https://www.ebay.co.uk/usr/simons_electronics?_trksid=p2047675.l2559
 

Offline vikisonline

  • Contributor
  • Posts: 5
Re: Need a low latency wireless transceiver.
« Reply #2 on: May 18, 2013, 07:40:39 pm »
One use case:
-arm processor receives an interrupt for a camera hotshoe. Sends wireless signal

-slave receives wireless signal. Triggers flash unit x number of times. has to happen all within an exposure.
Generally under 1/500 of a second.
 

Offline Simon

  • Global Moderator
  • *****
  • Posts: 13831
  • Country: gb
  • Did that just blow up? No? might work after all !!
    • Simon's Electronics
Re: Need a low latency wireless transceiver.
« Reply #3 on: May 18, 2013, 07:44:47 pm »
sounds like you need to have a 4 bit address system that gives you 16 addresses so you can use the 16th as a universal address for all 15 units, or do that same with more bits if you want over 15 make 0000(0) your universal address, then you need a few bits of data to tell the receivers what to do. you will need a frequency not used by anything else or with a way of distinguishing itself.
https://www.simonselectronics.co.uk/shop
Varied stock of test instruments and components including EEVblog gear and Wurth Elektronik Books.
Also, if you want to get ripped off: https://www.ebay.co.uk/usr/simons_electronics?_trksid=p2047675.l2559
 

Offline vikisonline

  • Contributor
  • Posts: 5
Re: Need a low latency wireless transceiver.
« Reply #4 on: May 18, 2013, 07:51:41 pm »
Any wireless modules you could recommend?
 

Offline Simon

  • Global Moderator
  • *****
  • Posts: 13831
  • Country: gb
  • Did that just blow up? No? might work after all !!
    • Simon's Electronics
Re: Need a low latency wireless transceiver.
« Reply #5 on: May 18, 2013, 07:54:57 pm »
No idea, I don't do wireless
https://www.simonselectronics.co.uk/shop
Varied stock of test instruments and components including EEVblog gear and Wurth Elektronik Books.
Also, if you want to get ripped off: https://www.ebay.co.uk/usr/simons_electronics?_trksid=p2047675.l2559
 

Offline Rasz

  • Super Contributor
  • ***
  • Posts: 2279
  • Country: 00
    • My random blog.
Re: Need a low latency wireless transceiver.
« Reply #6 on: May 18, 2013, 08:27:04 pm »
-nRF24L01P: also nice, cheap ($2.5 from china) but can at most have 6 slaves for one master.

I suspect flash units wont have anything to say back to the master, so you dont really need slaves, just listening radios
Next Hope Badges were based on this chip and Travis Goodspeed was able to sniff arbitrary traffic with them = you dont need any pairing.  You can just send with master and sniff with slaves for "magic packet"
Who logs in to gdm? Not I, said the duck.
My fireplace is on fire, but in all the wrong places.
 

Offline vikisonline

  • Contributor
  • Posts: 5
Re: Need a low latency wireless transceiver.
« Reply #7 on: May 18, 2013, 08:50:54 pm »
Hmm that might just work :D Thanks. I'll look into that further.

Out of everything this chipset has the lowest latency I have seen so far. With the right config you can get down to something around 250 micro-seconds for an 8bit message. If they don't actually need to pair and I can just sniff that is great. I wanted them to be able to report back, maybe for collecting battery stats, but like I said thats not important.

And an other interesting project to look at :D
 

Offline G7PSK

  • Super Contributor
  • ***
  • Posts: 3644
  • Country: gb
  • It is hot until proved not.
Re: Need a low latency wireless transceiver.
« Reply #8 on: May 18, 2013, 09:23:35 pm »
All the slave flash guns I have seen have been light operated, the master flash is fired and all the slave units have a photo cell that triggers the unit, works in all the instances I have seen.
 

Offline codeboy2k

  • Super Contributor
  • ***
  • Posts: 1838
  • Country: ca
Re: Need a low latency wireless transceiver.
« Reply #9 on: May 19, 2013, 12:40:27 am »
light works well as a slave flash.. but I think there are problems with it when there are more than 1 slave, and you have multiple slaves, I don't know if they all flash at the same time.

here's a table from a PhD students dissertation thesis, he studies clock synchronization in networks of wireless embedded devices.

here's the full paper.  Actually a good read.  http://e-collection.library.ethz.ch/eserv/eth:4579/eth-4579-02.pdf

In that paper he tests 4 different wireless chipsets. It turns out the TelosB platform has the least latency, and that platform uses the msp430F1611, the TI CC2420 radio, and TinyOS.


« Last Edit: May 19, 2013, 12:45:48 am by codeboy2k »
 

Offline amyk

  • Super Contributor
  • ***
  • Posts: 6526
Re: Need a low latency wireless transceiver.
« Reply #10 on: May 19, 2013, 10:50:32 am »
I don't know where you are but if all you want is on/off type signaling then 433MHz transceivers with an RF remote control encoder/decoder will probably give the lowest latency: http://www.laipac.com/easy_434a_eng.htm
If this band is legal to use in your area it might be less crowded/susceptible to interference than 2.4GHz
 

Offline vikisonline

  • Contributor
  • Posts: 5
Re: Need a low latency wireless transceiver.
« Reply #11 on: May 26, 2013, 06:04:19 am »
Thanks.

Didn't know you could simply sniff like that with the nrf. The latencies are not great but should work

That research paper looks like an awesome read. I have a thing for well written papers. :-D
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf