I read teh rules want the defined frequencies used that have been regulated for rc boats at competitions. Ive looked for ic's that match (74mhz if I remember) and there was only 1 and it could only transmit or recieve (I cant remember which one) and it was expensive. On the other hand I can find ic's that do something in the 300 or 400 mhz range, 900mhz 2.4ghz etc... for very cheap that can do both transmit and recieve and at speeds of 500kbaud/sec. How stringent are the wireless rules at competitions? I would figure if I could hop on a few different channels it shouldn't be the end of the world.
um... let's see... most people just use hobby-brand electronics, readily available online and in hobby shops, for $50-$200, depending on the number of channels, computer, 2.4ghz, etc. If you want to build your own unit, it will be significantly more expensive than a store-bought one. On the other hand, if you've got the skill, you can build in some neat features.
Here's the deal... in many bands, you can use the frequencies under Part 90 of FCC rules as a secondary user, meaning that you must accept all interference generated by primary users and cannot cause any interference to primary users. Most of the tiny modules that one sees in Mouser/Digikey/etc are already certified with the FCC and are good to go as-is. However, you need to check the frequency that you're looking at using to see if your proposed use is allowed, and if you plan on ignoring the FCC, at least find out what its intended use is; some are use in medical applications and it might be bad to cause problems there. Realistically, at the power levels the little chips can generate, you won't interfere with anyone's stuff, but its worth noting. The big downside for me is that if you use a module in a non-intended use, you won't be able to brag about it in a public forum, like say, the internet, bercause people actually DO look at those who care and could report you. Not saying don't do it, just that I don't think it's worth worrying about the hassle or the threat of a $10k fine from the Feds. Like Kotori says, you can get a great, funcitonal, legal radio for far less time and money than implementing your own from a Zigbee or such. Far less. And realistically, with the advent of 2.4GHz radios, you have far more frequencies available than most clubs can dream of getting on the water at once.
The particular IC I have my eyes on is the CC1100RTKR. $3.15 each cdn. It requires very few external components ( a few resistors, caps and of course an oscillator) and it supports a couple different frequencies (900mhz & (300mhz or 400mhz depending if you reside in us or eu if I remember) researched the specifics long time ago and will refresh myself during the pre-order process). From the datasheet: Suited for systems targeting compliance with EN 300 220 (Europe) and FCC CFR Part 15 (US). I have the 40 pin microcontrollers already ($7 each if I remember) and I have the knowledge electronically to throw it all together. I plan on using old treble/bass controls from a blown up stereo of mine to control the turret directions. This would give me a two-way communication/computational system for roughly $25 worth of components as well as having roughly 32 I/O pins minus a few for the wireless communication on both the reciever and on the vessel. This communication also would allow multiple vessels to run on the same channel as the chips have built in hardware packet handling (device address, crc checking, etc...) I would think the $50 device you guys have mentioned wouldn't offer the same flexibility (although it does have a very good chance of looking prettier). I have done some homework (probably about 10 hours worth) as to what frequencies and FCC regulations etc... The thing that worries me most, is I saw a page that pretty much was saying the 74mhz must be used at proper matches etc... but I also saw elsewhere in videos/writeups/etc the mentioning of other frequencies being used 900mhz, and 2.4ghz. So as much as I would prefer to do it my way; it would be silly to put in all the effort of building a vessel that could not compete in matches because of the frequency it is running on. I am guessing based on your responses that frequencies for matches isn't the issue, but rather you look apon my project as being very time consuming(for me, I would like to think I could handle the wireless portion in a weekend for the first system (subsequent systems will just be replicated and done in a short amount of time)).
Well, if you have the skills, go for it That said, check your clubs rules on allowable frequencies; Some specify 27MHz, 75MHz, 2.4GHz, and legal ham bands. Bands may be different if you're operating in Canada. Using gear legal under Part 15 may raise range issues due to the power, although I'd think one could (for the user-end) use a directional antenna to increase this. Having a ship with telemetry could be cool.
information for those who are interested: http://docs.tinyos.net/index.php/CC1100/CC2500#Range_vs._Frequency (700->800ft + more if you start slowing down data rate etc...) I myself would be happy with getting 1/10th of what they say they can get. Knowing how far a 900mhz phone can go, I think its quite possible to achieve my desired 1/10th of what that site says. Edit: http://www.alibaba.com/product-gs/207127604/RF_modules_CC1100_high_data_rate.html (package says 500m) ^not sure if they have added an amplifier or not, but they definately have slowed down the speed. (I myself am not interested in this predone package but maybe someone else is) -> I haven't found any mention of frequenzies on the club site. When I get in contact with them, I will find out. ->What about the major competitions? You mentioned 27, 75 and 2.4ghz but what about the 3xx or 4xx mhz, or the 915mhz?
If you're in the USA, an amp is likely illegal, as Part 15 limits you to 1/2 watt. I can't conceive of a 1/2W at those frequencies getting nearly that range in actual use; it sounds more like marketting than engineering figures. That said, If you get 200 feet of range, that's probably plenty for most RC naval combat applications, except maybe really big lakes like a Nationals-type event. Looking at the module you linked to, they say that other frequencies are possible; with a minimum order of 5 units, if they could do something in the 430-440MHz range, that would make a transceiver based on it ham-legal, and hence you could stick an amp on it up to 1.5kW in the US with the appropriate ham license (costs $14 to take the test, which is easy-peasy). THAT would be cool. Realistically, 1 or 2 watts with the channel-hopping capability and the data rate acheivable would be worth the effort. Make the handheld unit the master unit and the shipboard part the slave unit, thus meeting the requirement for remotely-controlled radio transmitters to be able to be shut down by the operator, making it legal for the shipboard unit to send back telemetry. Tie the telemetry in to a small LCD display on the controller and you'd be able to see damage reports, ammo expended, things like that. Heck, you could have a processor on the master unit compare rate of water level rise inside the hull at several points versus known pump capacity and give you estimated time to sinking on the fly. I like it.
Went and looked, now that I'm home... (These are valid only in the US, as obviously the FCC doesn't apply in Canada, EU or other foreign countries) 74MHz is in a band allocated to astronomy 300MHz and 400MHz are allocated to US Dept of Defense aeronautic radios 900MHz is in a tight spot with some business stuff and amateur stuff crammed together around that freq. Although if one got the lowest amateur license it'd be legal from 902MHz to 928MHz. I looked at the RF module linked to above and the stock freq they list is, how lucky are we, right in an amateur band, where according to the amateur band plan, one is supposed to use remote control links! Hmmmm... Buy some of those little modules, and build an amp to take it from .05W to .5W and you're good.
Hmmm. And, for about USD$30 you can purchase a ready-made Hobby King 2.4gHz TX and 8 ch hobby RX module which are already legal under NAMBA and other rules - no cobbling necessary. Or start with a $33 Hobby King 6 channel 2.4gHz radio and mod it to your heart's content with your microprocessor. You are at least beginning with a known working system, and the RX portion is done for you. These units are transceivers, by the way, if you have the electronics oomph to hack them. The electronics is not the only time eater. Designiong and cobbling a useful interface takes time, too. Beginning with a case that has batteries, antenna, and some controls already mounted, can save a lot of time and effort. Took very little time for me to mod the radio to a slide pot and a 3 position switch instead of a second joystick, and to replace another pot with fire buttons. Regardless, if you want to "roll your own," more power to you. A suggestion -- save the radio until the ship is ready for it. Once the ship is ready to battle, there may well be better/cheaper radio technology available. And, make sure your club's governing bodies approve the frequencies - some clugs have specific lists, and some, until relatively recently, did not allow the now common 2.4gHz. Cheers,
