A simple research tool

[Luke Brane]

Hi Folks,

I was hoping to plumb the depths of knowledge found on this legendary email list.

I have a question about the best setup for a simple wireless switch. 

The short explanation is that I need to make a switch that can remotely and reliably  send a wireless  "go" signal to another device from about 10-15m away. The device can take digital input using one of these. That "go" signal will begin the data collection simultaneously flashing a light on the switch that will allow me to sync the multiple cameras that will be recording the trial to the start time of the data collection.

I was thinking of using some arduinos and a couple of 2.4ghz transceivers like the nRF24L01, but I thought I would put it out there for the experts to comment on.  I have a decent working knowledge of arduino and some of its associated accoutrements, but have never done anything wireless before.

Any input or feedback would be most welcome.

Best,

Luke

[James Marquardt]

Hello

You might want to look at BLE.  I just did an experiment exactly lime what you are looking for and I was able tonreliably transmit almost 300 feet open air

Jim

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[Dan Lavin]

I recently did a couple of projects using arduinos and pairs of nRF24L01s.  These packet radios work remarkably well and are easy to work with.  If you have line of sight you should have no problems with the distance you want, but if if you have walls in between you could have issues.    There is a lot of stuff on line on these chips and a good library available--Check out

https://github.com/maniacbug/RF24

I started with an online example and modified it for my projects.

Unless you are comfortable with a soldering iron,  get one of the readily available adapters to make wiring easier. 

The radio modules and the adapters are less than $2 each on ebay out of China.

[Luke Brane]

Thank you both for your input, I really appreciate it.

Dan, I also noticed that those modules were a very attractive price.  It made me almost skeptical that it could do what I need, but it sounds like you had success.  I am comfortable with soldering, so that shouldn't be an issue hopefully.  Out of curiosity, what arduino model did you use for your project?

Thanks again.

-Luke

[James Marquardt]

I bought a couple of the 24L01’s from Amazon for about $6.00 a pair.  I picked them up with some other “toys” for one shipping price.  The one thing with them is that unless you set up a protocol in software you can sometimes get false packets and since your requirement is reliability I recommended the BLE(you could also use regular Bluetooth)  With BLE you match the transceiver pair so it cuts down on the potential for false packets being accidentally processed.

 

Jim

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[Jonathan Dahan]

Xbee I'd pretty great for this kinda stuff too - relatively simple to configure, a bit expensive but if you use v1 protocol point to point is pretty much just a 'wireless wire' with good speed range and error correction. I used it to make wireless pressure sensitive drumpads for a performance and they were spot on..

[Dan Lavin]

I used two pro minis for one project and a pro mini and an uno for the other.  I also used a nano in the development process.  I did have some trouble with a leonardo, but I suspect that the problem was with Mega328 specific watchdog time code unrelated to the radio link.  Since the radio interface is SPI, you should be able to use any arduino.

Note that you need to supply 3.3 volts to the nRF24s and the pro minis don't supply it, so you will need an external regulator if you use pro minis.  I ended up using an adapter, just for the regulator in one instance.

Please feel free to contact me directly if you need more details.

[Chris Stratton]

I'd have to recommend the nRF24L01, too.

And I say that having done a lot with BLE. BLE solution in prototype
quantity are not only more expensive by a factor of about three, but
unless you are planning to talk to a smart phone or some gadget which
already has it, or spend the time to run your whole project on a
BLE-enabled MCU like the nRF51822, it's probably not worth the bother
of its greater complexity.

With regard to the 3.3v issue and small form-factor Arduino-type
boards, I'd be tempted to get the 3.3v, 8 MHz version of the ATmega
board for that purpose anyway - you probably won't need the 16 MHz
speed, and the slower, lower voltage version gives you more options
for battery power and conservation.

If trying to do experimental setups with the nRF24L01 modules or
anything else with breadboard-unfriendly pins, a very handy method can
be a wire wrap tool. Hot glue or foam tape the radio board to the
MCU board (giving the antenna some free space), then use a wire wrap
tool on the header pins to quickly join the two circuits. Although
standard header pins are only a third the length of the old wire wrap
pins, they still have room for one or two connections per pin.

That said, the nRF24L01 modules are so cheap, that I used a hot air
station and pliers to extract the header pins from one and substituted
22 gauge wires for breadboarding. The female-male jumper pin sets
could work too, though watch out for bad ones where the crimp caught
only insulation and no wire!

[Luke Brane]

You guys are the best!  Thanks for all the great replies, everyone.  I really appreciate it.

I think I'll try this with the nRF24L01's first and keep BLE and XBEE in mind if I run into trouble.  Dan and Chris, thanks for the detailed info, that is a huge help. 

Best,

Luke

[jpbar...@aol.com]

Hi All,

I once used a Linx Technologies  TRM-433-LT  433 MHz transceiver  for a project.

It is expensive (>$12 in low quantities), is limited to 10Kbaud, and if the sensitivity is kept at the default you get random noise in rx mode that requires a protocol with CRC checks.

I used it for a short range application, using planar antennae on the boards, but they spec the parts to 3000'.

They have some new modules that I haven't used and some old and new ones can be used for simple On/Off IO on each end without the need for micros.

I am happy to hear about good results from the board for the nRF24L01 and a quick search shows a Sparkfun board with a version with a "+" suffix with some new features.

It has an onboard 3.3V regulator, but I guess the added expense may only be justified for a prototype.  It's a part I should consider using.

Someone mentioned that the nRF24L01 modules can be purchased from China for $2.

This is off subject, but I don't know how they can sell this stuff so cheap!

But I believe that sometimes parts may be counterfeits.  Some of you may have heard of the knockoff FTDI chips and adapters that came onto the market and FTDI's release of a driver update that when detecting a knockoff chip disabled it.

I wonder if anyone has had any such issues.

Joe

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-----Original Message-----
From: Luke Brane <luk...@gmail.com>
To: nycresistormicrocontrollers <nycresistormi...@googlegroups.com>
Sent: Fri, Jun 5, 2015 10:41 AM
Subject: Re: [NYCR:Microcontrollers] A simple research tool