RF Remote Sensor and Controller

Discussion in 'The Projects Forum' started by jerkeife, Jul 23, 2013.

  1. jerkeife

    Thread Starter New Member

    Jul 11, 2013
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    0
    Hello Everyone,

    This is my first post here and my first dive into electronic design in general. First off I apologize for the long post; I do like to do my research and I am at the point in my project where I need to begin to order components. A little about myself before I begin.

    My first name is Jeremy and I am currently enrolled at the University of Wisconsin-Milwaukee pursuing a degree in Mechanical Engineering and am about to start my senior year. My programming skills currently start and end with a basic Java course that is required by my major. My electrical knowledge begins with a few basic physics classes and ends with the most basic circuits class I have ever encountered. It dealt almost exclusively with DC(thankfully I plan on using DC) and we just made it into AC and three phase but it would be a lie if I told you I knew anything about AC.

    Now to my project. I am attempting to create a group of sensors and a central controller/revceiver that deals with remote motion sensing. I want to use this to monitor certain trails and crossings that are difficult to see when hunting, and I want to be alerted when there is movement on that trail. To begin I would like to focus on shorter distances of about 300 ft (a little under 100m for those who are more accustom to the metric system).

    Due to the distance I am attempting to cover and the fact that it will not necessarily be line of sight, I chose to use an RF signal on one of the open frequencies (434 is what I have chosen so far-easiest to find components with adequate explanations for a newbie) instead of an IR signal. My original plan was to use the central controller to turn each component on and off but after exploring the cost of the extra components, I decided to go with sensors that were constantly on once placed in the field (still has an on/off switch) and a controller that could be turned on and off. My original operation set-up can be found in attachment "Controller-Sensor Operation."

    Now to my original set-up-please see attachment "Controller-Sensor Setup" as I am unable to figure out how to place it in my post here. Since formulated my original plan, I have done some research and I was able to find components with a relatively low current consumption. Due to that and the added bonus of reducing the number of components and an actual draw in current consumption, I eliminated the remote on/off control of the sensor (as previously stated). The remote sensor and controller schematic can be seen in attachment "Controller-Sensor Basic Schematic." Since creating that diagram I have come to realize that some microcontrollers have an oscillator/resonator within them. I left the component on since idk what microcontroller to use.

    I still have an infinite number of questions that need to be answered but feel that information is best learned from struggling with the question and then researching and finding the answer for myself. However with money on the line, I figured it would do me good to get the input of those who know more than I do.

    First of all I really wish there was a place where I could get all of the components that I need at the cheapest prices available. So far I am ordering components from DigiKey, Jameco, and Sparkfun. I have also explored Rentron, linx and a few others whose names currently escape me. Are there any other sources that you can suggest? I like to support local companies, or at least those in the USA. No offense to those outside the USA, but I like to support those close to me who are also struggling to keep up.

    Second is in regards to the microcontroller. I will admit that I have no idea what I am talking about here. If somthing I say is wrong or just plain old stupid, please correct me; I am a complete newb. On the other hand I am not afraid to get my hands dirty and learn some programming languages other than basic Java, in fact I welcome the challenge it presents. So far from what I have read, PIC seems to be the type of chip I would like to use. It seems to be one of the more prominent and better supported type of chip out there and from what I understand, it runs on C and there are many development boards and programmers available. What I am currently looking at purchasing is a PICkit3. Specifically this one:http://www.ebay.com/itm/Easy-To-Use-USB-PIC-chip-PICKit3-programmer-ICSP-PICKit-3-Full-Pack-A-/111117927659?pt=LH_DefaultDomain_0&hash=item19df2504eb#shId. Is this all I need to program/debug a 18 pin uC? I am seriously lost in this part of my endeavor.

    I realize this is a long post already so I will stop with the questions here. If anybody actually bothers to read this entire thing and has any questions please ask away. As I have said I am completely new to this and may be completely and utterly incorrect in everything I said. Please enlighten my to any mistakes I have made.

    Thank you for actually reading this and providing any insight you may have.

    Jeremy
     
  2. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
    1,758
    98
    The 433 MHz RF modules are very simple and may not be reliable beyond 30-40 ft.

    Take a look at XBee modules, slightly more expensive but support mesh networking and are bi-directional. They also have rudimentary I/O and a UART.

    MPLABX and XC8 are what I'm currently using. I was using Swordfish BASIC but wanted to get a grip on C.
    As for 18 pin PICs the 18F1320 is pretty nice and has a built in oscillator. The PICkit3 is good choice.
     
  3. jerkeife

    Thread Starter New Member

    Jul 11, 2013
    3
    0
    https://www.sparkfun.com/products/10534
    This is the rf transmitter I planed on using. The specs list the distance at 500ft. I realize that distance is listed for perfect conditions but 30-40 ft is less than 10%. That's quite the difference. Thanks for the heads up.

    I was trying to make this as inexpensive as I could given the fact that its my first attempt at anything electronics related. Looks like I may have to rethink my strategy.

    Thanks again!
     
  4. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
    1,758
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    Do you have any walls or obstructions? Any other RF devices nearby? Perhaps a directional high gain antenna might help. You'll have to buy a TR pair and test the range. IMHO you'd be lucky to get 100'

    Read through the comments on the sparkfun link.
     
  5. sirch2

    Well-Known Member

    Jan 21, 2013
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    I've used a module similar to that and they do pick up a lot of noise so you need some kind of "protocol" to be able to detect valid signals from noise.

    I guess you are not in the UK but RF Solutions have a good range of reasonably priced products - something like this http://www.rfsolutions.co.uk/acatalog/info_ALPHA_TRX433S.html might do
     
  6. jerkeife

    Thread Starter New Member

    Jul 11, 2013
    3
    0
    Any obstructions would be trees. The only RF devices that would be in the vicinity would be the other sensors. 100' isn't much. My plan now is to purchase these cheap components as a test run and then purchase the something more appropriate for the actual device once I know I am actually able to make them. Thanks.



    Would setting an address to the encoder/decoder be sufficient to help cancel the noise? Or at least a step in the right direction. As I have said, very inexperienced here.

    I have taken the first step and ordered a PICkit3
     
  7. sirch2

    Well-Known Member

    Jan 21, 2013
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    I was trying to send a simple On/Off to trigger an interrupt on the microcontroller. The thing I found was that when the transmitter was sending out a signal it worked fine but when the transmitter stopped the AGC on the receiver would ramp up the gain and I would get spurious signals from the receiver. So you need some way of knowing that what is coming from the receiver is a valid signal, not noise. Things like XBee and the module I linked to take care of this for you.

    What I did in the end was to send a pulse train at a set frequency for 10 pulses and then send 2 double width pulses. On the receive side I checked for a sequence of pulses at the set frequency followed by 2 double width pulses. If I received this sequence I executed the code on the receive side.


    If you are going to have multiple transmitters you will need some way of identifying which one you are receiving.
     
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