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First Arduino Project

dukeofmarshall

So I got my first Arduino (Mega 2560) two weeks ago. I've been playing around with it and learning the basics and what not. I have decided on a useful project and have been thinking through it and researching out the parts. The parts have been ordered and on the way. So I decided for the mean time I would go ahead and do a wiring diagram of how I think it will eventually go all together. But since this is my first project I thought it would be prudent to have the wiring diagram reviewed by those of you who know what you're doing already.

 

My project consists of:

  1. 20x4 LCD Module
  2. An RTC Module
  3. 2 9g Servo Motors
  4. A DHT22 Temperature and Humidity Sensor
  5. A 4 Channel Relay Shield to Control a 120 volt line and a 12 volt line

 

My plan is to provide a 5v line for the Arduino itself, a 5v line for the other 5v components, a 12v line, and a 120v line. I plan on using an Arduino Nano in the project so my Mega will still be available afterwards.

 

So if anyone has the time and is willing to look over the wiring diagram real quick, I'd sure appreciate any feedback or suggestions for improvement. Thanks.

 

image

  • in reply to dukeofmarshall

    Todd, for me the issues with using that specific relay shield are:

    • A Peter mentioned, there's an expectation that shields are safe to handle
    • Is the complete system rated for the load (Peter's question?)
    • The close proximity of relay 4's outputs and the low voltage pins
    • Support of the board, if you attach it with 3 mounting screws does it provide adequate support for the screw terminals. Will the board crack/tracks break whilst you are fitting the cabling.

     

    Other things to think about when building such a project, this is not an exhaustive list but should help you make a safe project.

        1. Is there anything conductive (metal screws etc) that connects the outside of the case to the inside.
        2. Are there any large holes that a finger would fit into? Would that finger touch live parts?
        3. Are there any small holes that a screwdriver would fit into? Would that touch live parts?
        4. Are your cables properly strain relieved? One good way to handle that is to use IEC socket, that avoids the issue of cable strain relief. Although see point 1 about screws/bolts etc. You can also heatshrink or boot these sockets so that the live parts are not accessible.
          image
        5. In the case of a short or problem with the load, is there some form of protection such as a fuse?
        6. Does there need to be some kind of suppression on the relays to stop arcing of the contacts or radio interference? (load dependant)
        7. Is your cabling rated for the load (and higher rated that the protection device) e.g. 5A cables, 3A fuse.
        8. How will you test it safely?
  • in reply to Robert Peter Oakes

    I'll be using one of the relays to control a 12v CPU fan and the second relay I'll be using to control a standard 120v CFL light bulb as a heat source. I'm going to need to maintain a temperature of about 95-100 degrees Fahrenheit.

  • in reply to dukeofmarshall

    Are you making an egg hatcher? I can't imagine that a 120v compact fluorescent lamp puts out much heat, why not use some 12v halogen lights as a heat source?

  • in reply to Workshopshed

    Andy,

    Thanks for responding. I'll try to answer your questions in order.

     

    1. No, nothing to connect the power/control box to the outside. Nothing metallic/conductive anyways except the wires going into and out of it. But they'll be coated or insulated from the factory anyways.
    2. I hadn't planned on any large holes that things could fit into the power/control box. Though I'm not sure if ventilation will be needed for that yet. Would that be a good idea to add to it?
    3. Same as 2
    4. Yes, they will be. I always believe in proper strain relief and contingency.
    5. I hadn't previously planned on putting in any fuse or breaker, but now that you mention it that'd probably be a good idea.
    6. Not sure what you mean, but I had planned on insulating the top of the screw terminals with electrical tape or something.
    7. Oh yeah, plenty of wiggle room there.
    8. Visual inspection and multimeter inspection of various points.
  • in reply to Workshopshed

    Andy,

    Yeah, it's an automated incubator. I thought that should be something I could use in real life and would be a fairly straight forward project to get me started with.

     

    So a 12v halogen would produce the needed heat?

  • in reply to dukeofmarshall

    Hi Todd, I'd not intended those to be questions, just food for thought whilst you are designing / building it.

     

    On point 6, when relay contacts are very close there might be a spark that jumps the gap, this causes damage to the contacts and radio interference. Look up snubber circuits or arc suppression.

     

    I believe that you should be able to get lower voltage lamp that produces heat. Halogens definitely put out quite a lot but there might be other options that work better in this case, there's definitely egg people using halogens (from my limited googling). That would resolve your high voltage issue.