having issue with my senior project

Discussion in 'The Projects Forum' started by SchmitTrigger, May 23, 2014.

  1. SchmitTrigger

    Thread Starter New Member

    May 23, 2014

    I`m designing an automated greenhouse, using PIC18f4520 as the processor.
    The circuit contains, the PIC circuit including:
    LMB402CFC as the LCD
    a 3*4 Keypad.

    As input to the circuit, I have three different sensors,

    Soil Moisture sensor

    As output to the circuit, I have four different actuators:

    LED light,

    The outputs function under high voltage of 220V.
    I connected the outputs to the PIC, using open switch relay connection.

    The circuit also contain a PushButton and a Buzzer.
    For the power distribution, I have one 9V battery connected to a voltage regulator, with capacitors and its I/O pins.
    the output pin, is connected to one side of the sensor.
    the ground of the regulator is connected to the PIC ground.
    the ground of 9V is connected to the pic ground..

    I have another 9V source, connected to a voltage regulator, where the output of it is connected to the + of the pic, the ground of it, is connected to the ground of the pic, and the ground of 9V is connected to the ground of the pic.

    Ihave a 12V battery source, as a supply for the open relay switch.
    the ground of 12V is connected to the ground of other 9V batteries, which in turns are connected to the pic ground.

    I`m having an issue of a noisy ground, where I was adviced to put 100nF ceramic capacitor parallel with 1uF electrolytic capacitor, between Vss and Vdd.

    The problem is:

    Each day new problem occurs, sometimes random decisions by the PIC, sometimes the LCD don't bright at all, sometimes bright well, sometimes.....

    The system is unstable
    Any solution possible?
  2. MrChips


    Oct 2, 2009
    One of the problem is digital circuits do not like having long cables.

    You may have to move from the reuseable protoboards to a wired protoboard such as Vero or Vector board or a printed circuit board.
  3. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    That's an impressive looking setup! :eek: :)

    You are running 1uF caps on your 7805 regulators, I think that is too low. 47uF is a good value.

    Other than that, I think you might have bad connections on your breadboard. They are notorious for getting corrosion in the plugin terminals and dissimilar metals issues over time, and are likely to give bad connections if used for long periods.
  4. enggricha


    May 17, 2014
    how did u figure out you have a noisy ground??

    Going by your description of your LCD behavior it could as well be your power supply not giving enough current under some conditions! what power source are u using and Y the multiple power sources?
  5. tshuck

    Well-Known Member

    Oct 18, 2012
    If your schematic is any indication of the way you have physically connected your grounds, you've created several ground loops, which could cause erroneous behavior.

    In addition to what the others have suggested, I would check your ground connections. Measure your ground voltage at the batteries and work your way back. If you have any significant voltages, you have ground loops and you should look into using a single-point ground, where all grounds connect to a single point.

    What kind of power source is the 12V source? Battery? Wall-wart? What are the specs?