Suggestions on RF module for handheld app.

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#1
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Hi Guys,

I am thinking of making a handheld app where I have to control a remote (50 feet through walls) stepper motor. What are some good transmitter/receiver modules I can use for this? Battery life is important and device will be in sleep mode most of the time.

Data rate can be around 2400 bps.

I was thinking of the sparkfun 315MHz transmitter module, but I could not get a firm yes or no answer on whether it is FCC certified. (I have asked Sparkfun customer support)

Any other ideas on what is the simplest, smallest RF module I can use? Should I go for Xbee?

Thanks.

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Any ideas anybody?

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XBee is simplest to use because it's plug and play in terms of two-way data with error correction and addressing.

There are cheaper ways to go if you want to do more of this yourself.

Your app sounds quite simple.

Consider too the HopeRF transceiver modules. Some sold by SparkFun

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if you go make your own, look into the nRF24L01P. Cheap(ish) chip, high data rate, low power consumption.

I have used these numerous times for all sorts of projects and they are incredible :)

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Depending on material of the walls I would recommend either a 900MHz or 2.4Ghz ZigBit. The mega1281 on this modules could also perform the task of the application controller.

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I've been using the TDH2 from Radiometrix. It is a true data in/data out module straight out of the box. You don't have to do anything. You will only need the TDL2 which is the same module but less RF power. And being a 433MHz module, it will go through walls a lot better than the higher frequency transmitters. The downside is they aren't that cheap. But depending on how many you need, the simplicity of them will far outweigh the cost.

Matt

http://www.radiometrix.co.uk/pro...

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Thanks for the suggestions,guys. Now comes the million dollar question; which of these modules are FCC certified for hobby projects (NOT selling anything)?

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The Radiometrix ones are probably FCC certified, check the web site.

Leon Heller G1HSM

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Radiometrix have various products which have various ratings for FCC, ETSI etc. . . However. . . .

As soon as you take ANY approved product, and put it in something, or connect it to something, you are then required to get the "new" product re-approved. So an FCC certified RF module connected to an FCC certified power supply with an FCC certified microcontroller board, will still need to be recertified as a complete unit. . . . However . . . .

For hobby use don't worry. Stick with stuff that is ALREADY certified and leave it at that. It would only become an issue if you start selling a product.

Matt

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Quote:

As soon as you take ANY approved product, and put it in something, or connect it to something, you are then required to get the "new" product re-approved. So an FCC certified RF module connected to an FCC certified power supply with an FCC certified microcontroller board, will still need to be recertified as a complete unit. . . .

Reference, please?

That isn't my understanding, and isn't the way we have done RF projects in the past. We've used certified modules hooked to our AVR apps, and then fuggedaboudit.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Well I guess I am looking at Australian law rather than USA's FCC laws, however our testing agency told us the same applies over there. Sorry I don't have any official laws at hand other than emails from our testing agency.

But to reference it. Our company makes radio repeaters. We take 25W radio transmitters which are FCC/ETSI/CE certified, add in our own interface boards which are certified, throw in a power supply again certified, plus some batteries etc. We were told that even though every single sub-assembly is certified, we would have to get the "whole product" recertified because its all housed in one box and users cant access individual parts. Now one big advantage is that because we can supply the test certificates for each sub-assembly, the testing agency can do the tests a lot quicker, and therefore cheaper.

So back to you, have you got your AVR app certified? I thought FCC required anything over 15mW to be certified. Now I know your app could be under that anyway, but probably not once you connect an RF module. Again I'm not in America, so I don't care about FCC rules, but we do get our stuff FCC certified since it doesn't cost anymore $$ when already testing for more stringent ETSI rules anyway.

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This CYA sheet supports your position:
http://www.radiotronix.com/downl...

However, let's drop the enclosed RF module part, and the doc says

Quote:
Simply put, the user of the Radiotronix FCC certified module must ensure that the application that
they are putting the radio into is already compliant for Unintentional Emissions (without the radio
even being inside the application).

OK, let's explore that: If we use those "rules", then every AVR app needs to be "FCC certified" so that it doesn't have unintentional RF emissions. Name two AVR apps with no embedded RF subsystem that go through FCC certification.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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2.4GHz and 900MHz are unlicenced in north america so you can use them with various ourput power. I'd consider doing zigbee perhaps or something that gives you a built-in mac layer to make your wireless application more robust... because... you will loose packets... and it's nice to have a means of retrys and stuff. Smaller pcb antenna with 2.4ghz too. The lower frequencies penetrate better but are usually a lower bit rate. Also, nothing really goes thru re-inforced concrete very well. 2.4GHz bounces better and is globally unlicenced.

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Those bands might be unlicensed but equipment using them must still be shown to conform to the regulations.

Leon Heller G1HSM

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theusch wrote:
This CYA sheet supports your position:
http://www.radiotronix.com/downl...

However, let's drop the enclosed RF module part, and the doc says

Quote:
Simply put, the user of the Radiotronix FCC certified module must ensure that the application that
they are putting the radio into is already compliant for Unintentional Emissions (without the radio
even being inside the application).

OK, let's explore that: If we use those "rules", then every AVR app needs to be "FCC certified" so that it doesn't have unintentional RF emissions. Name two AVR apps with no embedded RF subsystem that go through FCC certification.

Equipment that is sold in the EU must conform to the CE regulations for RF emissions and susceptibility. It's similar in the USA, except that the FCC only requires testing for emissions.

Leon Heller G1HSM

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I recall that Part 15 FCC A, B each have certain specs for both radiated and conducted signals. You submit a test report and get an approval number. No one at the FCC verifies. It's like automobile smog checks - money for the testers.

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It's the same in the EU. Where I used to work they hire the facility for a 1/2 day and do their own initial testing (it's quite cheap), fix any problems that arise and the unit passes the formal testing without any problems.

Leon Heller G1HSM

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Quote:

Equipment that is sold in the EU must conform to the CE regulations for RF emissions and susceptibility.

True. But that ain't FCC.

IIRC (it has been a few years since we developed an RF app) there is also a distinction between industrial apps, and ones that might be residential--you can't interfere with someone's home TV/radio reception, for example.

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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http://www.cclab.com/fcc-part-15...

It doesn't have to be an RF app to get tested though. A lot of products have what they call "unintentional emissions" which may be from high speed clocks or high speed digital switching lines. That weblink mentions anything over 9000Hz. When was the last time you made an app with less than 9KHz clock? I just picked up 3 different switchmode power supplies I have lying around and all 3 had FCC certification. One of the things they test for is also how well a device will ACCEPT emissions.

I'm sure you've all seen this phrase on a product.
1. This device may not cause harmful interference, and
2. This device must accept any interference received, including interference that may cause undesired operation.

But back to the original OP though. He's making a one off item for a hobby. It doesn't require testing.

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stevech wrote:
I recall that Part 15 FCC A, B each have certain specs for both radiated and conducted signals. You submit a test report and get an approval number. No one at the FCC verifies. It's like automobile smog checks - money for the testers.

You can self certify.

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jderimig wrote:
stevech wrote:
I recall that Part 15 FCC A, B each have certain specs for both radiated and conducted signals. You submit a test report and get an approval number. No one at the FCC verifies. It's like automobile smog checks - money for the testers.

You can self certify.

Really? I thought FCC required use of a "certified" lab, whatever that is, kind of like UL. Maybe high volume product companies use outside labs so that if there's a challenge later, they can do the blame game.

From working in 802.15.4 for several years now, it's interesting how the regulations vary widely for max radiated power in the channel bandwidth, with or without antenna gain limits (more directional, more power permitted, in some locales), and the wide variation in spectral mask rules. Japan and France are by far the toughest, at least in 2.4GHz. For '15.4's 2MHz channel, 10mW is the EIRP limit in these countries. In some middle-eastern countries, there is a flat prohibition of the outdoor use of 2.4GHz. No doubt caused by the gold rush of metro WiFi (like Earthlink tried and abandoned for business model reasons).

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Quote:
Really? I thought FCC required use of a "certified" lab, whatever that is, kind of like UL. Maybe high volume product companies use outside labs so that if there's a challenge later, they can do the blame game.

I'm currently in the position of wondering about this myself. I know of a certain product that was recently given Grant approval by a certain TCB in the US/FCC. It appears that the Grantee did their own testing/report, but were issued a Grant/Certification by a well-recognized TCB.

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stevech wrote:
Really? I thought FCC required use of a "certified" lab, whatever that is, kind of like UL. Maybe high volume product companies use outside labs so that if there's a challenge later, they can do the blame game.

The following is a excerpt from summary of Part 2, Subpart J, provided by the FCC Equipment Authorization Branch, provides some general information concerning various FCC approval processes for RF devices: (I am thinking PartB devices is similar but haven't found that reference yet). However I have no direct experience with this so take this with the appropriate grain of salt.

Quote:
Certification: Requires submittal of an application that includes a complete technical description of the product and a measurement report showing compliance with the FCC technical standards. ......
....

Verification: Verification is a self-approval process where the applicant performs the necessary tests and verifies that they have been done on the device to be authorized and that the device is in compliance with the technical standards. Devices subject to verification include: business computer equipment (Class A); TV and FM receivers; and, non-consumer Industrial, Scientific and Medical Equipment.

From what I understand is that if you use a formal testing lab you can "self declare" conformance without the application process to the FCC.