ATMega2560 Based Controller Board

Hello all,

I am building a scientific monitoring buoy as a school project. For my sensors I am mainly using the Atlas Scientific sensors. I have been designing a controller board for the buoy that is based on the ATMega2560. I have designed a large chunk of it, and wanted to check that it would work before proceeding. I wanted to check that the ATMega would actually work in the board I have just designed and make sure I haven’t missed anything. I have been using the Arduino Mega Schematic to guide me a long so far, but I wanted to check I have done it correctly. So I was hoping that somebody could look at my attached schematic and point out anything I have done wrong. Thank you very much for reading and helping!


BuoyControlBoardRev1.pdf (41.8 KB)

BuoyControlBoardRev1.sch (398 KB)

You need 100nF cap at regulator input and 10uF cap at the output per page 4 of datasheet

Thanks for that, I have fixed it. As far as the rest of it goes am I good?

Need a 100nF cap on Each VCC/AVCC pin, so you're couple short. Need a diode in parallel with the reset resistor, cathode to +5, keeps any spikes from reset switch from fooling the chip into high voltage programming mode & acting hung.

You're not doing anything with 12V but knocking it down to 5V? So why not just bring in 5V instead?

This buoy runs off of solar and the solar system I have outputs 12v. Also other aspects of the system use 12v e.g. the strobe marker light on top. I've made those changes, so I am guessing I am good to start creating the radio circuit? I plan on having a 2W radio I believe this will give me enough range? It needs to travel 25km

Cheers, Will

Range will really depend on frequency and antenna. May need license also depending on frequency. I'll defer to the HAM radio guys for guidance there.

I am in NZ if that helps for licensing. It is travelling over reasonably low radio noise areas I believe so that should make it a bit easier. And is there anyone with experience using the Atlas Scientific sensors? I have seen that you can get Power Isolation circuits and was not sure if it would be beneficial in my case. Would it be a good thing just to add to ensure accurate results?

Link to the sensors?


Power Isolation Circuit:

Totara: It is travelling over reasonably low radio noise areas I believe so that should make it a bit easier.

The concern isn't so much getting your signals at the other end, it's breaking the law by transmitting at illegal power levels. Generally, unlicensed transmissions are limited to very low power levels (milliWatts). I know nothing about NZ laws but the laws are pretty comparable amongst first-world countries, and 2 watts is very likely to require a license of some kind. If your application here is for school, an amateur / ham license can probably be used, but amateur / ham licenses cannot be used for for-profit applications.

25km is a healthy distance for 2 watts, success will depend on your antenna and the sensitivity of your receiver. Unfortunately, a buoy that bobs about is going to forbid pretty much any kind of gain beyond a 1/4 wavelength vertical omni, so you will probably need a lot of gain via a pointed directional antenna like a Yagi on the receiving side.

I was planning on getting a license for it, and as this is not for profit it should be fine. Also would I be advisable to have a few more than 2W to help make sure the signal makes it in poor weather. Also is radio going to be particularly tricky to setup? Or would I want to investigate other options such as GSM or Satellite. I'm just trying to be power conscious, as I am just using 2 x 12v 18 aH SLA batteries.

Regards, Will

GSM, if you can get service, is likely to be much more power efficient. It transmits in short bursts so the transmitter doesn't have to be on for long, then you can send the GSM module to sleep for most of the time. GSM by default is limited to 35km range ( which would be just enough if there's a cell tower near shore.

Satellite should also be fairly power-efficient, but man that stuff is expensive!

If you want to roll your own, you've got some options. VHF ham radio usually uses the AX.25 packet format ( via a TNC ( attached to an ordinary voice-comm radio to implement FSK on top of audio frequencies. The data rate is quite slow so it can take a while to send a lot of data, not terribly power-efficient.

Another ham alternative is to use CW, or Morse code, which is by far a more power-efficient encoding. There should already be plenty of C/C++ code out there for sending Morse code from an Arduino, so the software side is easier. And PCs have been decoding Morse for years through the audio Line-In, so the receiving side is mostly done too. While CW is usually used on the HF bands, I would NOT recommend that as you don't want your signal to be heard halfway across the world. There is an allocation for CW in the VHF bands which would be far more appropriate. I'm not sure what kind of radios you'd need to use for CW on VHF, though. Just Google "CW on VHF" and see what's out there.

Oh and by the way, if you do get a radio appropriate for CW, you should be able to use the same radio for OOK with the Arduino VritualWire library -- same as you would a cheap 315/433MHz unlicensed RF module -- if you don't want to mess with Morse.

If you do use ham radio, you aren't allowed "encrypted" or proprietary data. You will need to publish the protocol that you use, so that anyone can listen to and decode your transmissions.

Here in NZ we get really good off-shore reception, so I think GSM will be a good option. Is there any special antennae I should be using for it ? And can anyone recommend a good GSM Module, I was thinking the Quectel M10 as I have designed a board with it before, albeit it never reached completion.

Do you have a source for those chips? There doesn't seem to be a US distributor for them.

Was planning on going with AliExpress

But is there a better chip with a good supplier?

Don’t know, not familiar with GSM chips. I designed a 2560/Quectel board recently, have been looking for a source for them.

Ok well if I do find a good reliable source, I will let you know. As for my power isolation question is there anybody who can give me a hand? Should I use them? For just $100 it might be worth it

Totara: Ok well if I do find a good reliable source, I will let you know. As for my power isolation question is there anybody who can give me a hand? Should I use them? For just $100 it might be worth it

Are you switching any electrically noisy loads? Motors/coils?

I may need to for some other parts of the buoy. Shall I add them?

Well I can understand the attraction of buying a ready-made isolation kit, but you can also implement the same protections with your own individual components for less. So do you care more about easy or cheap?