Help with Audio Art Installation

Discussion in 'General Electronics Chat' started by timspin, Jun 14, 2013.

  1. timspin

    Thread Starter New Member

    Jun 14, 2013
    Hi All

    I have a electrical type problem that I'm hoping someone (please) will be able to help me with.

    Im creating an audio soundscape art installation that will use 3 'sound pods' to create audio soundscapes when they detect movement (via Passive Infra Red sensor). Each 'pod' runs from 3 1.5v AA rechargeable batteries.

    Here is my problem, the installation is in a forest, and the exhibition goes for 3 months.
    So I need a SOLAR charging solution for the pods. Each pod draws 30uA in standby and 130uA when triggered and playing a sound recording.

    I have plenty of solar charges to choose form, only I also need some clever thinking around this. I need a solution that will enable me to keep my pods up and running for 3 months with no maintenance, which means I need the devices to charge and run at the same time.

    This is what Im thinking...
    As I cant charge and run at the same time I need a circuit to run the pods in standby (30uA) and charge the batteries. When the device is triggered I need POD to switch from Solar to battery, when the audio recording is finished to revert back to Solar charge for running the pod and for charging the battery. Unless anyone has another idea.

    Some specs to the sound module Im using attached.

    Does anyone now how to do this, could you help me? Im a OK with a soldering iron, no expert though, can follow circuit diagrams if forced to, I would rather buy a completed solution if any exist.

    I would be grateful for any help / considerations

  2. Razor Concepts

    Active Member

    Oct 7, 2008
    A circuit can run on the batteries and be solar charged at the same time. A diode from the solar panel to the battery prevents any power from going back, and the circuit should not be harmed with a little extra juice from a solar panel.

    Considering this will be a long term display, I would recommend you get a solar panel battery charging IC.
  3. timspin

    Thread Starter New Member

    Jun 14, 2013
    Thanks, how about just using an all in one commercial solar battery charger, would that work if I wired my sound module battery right into the battery compartment of a solar battery charger? (That way I would also have all the circuitry for efficiently charging battery without over charging). More of a hack than anything else, but simple.
  4. RichardO

    Well-Known Member

    May 4, 2013
    I would be surprised that the current is only 130 uA while playing a sound. 130 mA seems more likely for full volume. You need more like tens of milliwatts of power to make sound that can be heard in any but the quietest of environments.
  5. timspin

    Thread Starter New Member

    Jun 14, 2013
    RichardO you are correct, Operation current is 135mA, standby 35uA

    Razor - I have done some research - I can not charge and drain a battery at the same time, the ion flow has to be either going in or going out. Its been likened to walking forwards and backwards at the same time.

    I think I'm back to needing a circuit designed that can do this:

    1) Use solar panel to run device on standby (35uA) and charge batteries (3xAA)
    2) When the device is triggered batteries take over (135mA) and solar is stopped (or included in powering the device)
    3) After the audio file has finished the device goes back to standby (35uA) and the batteries are charged by the solar panel - and the cycle start again.

    Does this make sense, anyone fancy a go at designing this circuit s I can build it, or helping me with some pointers - is there a circuit I could purchase that would do this.

    Im currently planning on using GoalZero Nomad 7 solar panels -

    USB port 5V, 1.0A max (5W), linear regulated
    12V port 13-15V, 0.2A max (3W), boost regulated
    Solar port 6-6.5V, 1.0A max (6W), not regulated

    I really need some help getting this together.
    Anything appreciated.

    Kind regards
  6. RichardO

    Well-Known Member

    May 4, 2013
    I have been doing some thinking about your challenges in this project. Here are some thoughts for you to consider. Note that these comments do not necessarily answer your posted questions.

    Lets make some assumptions -- probably wrong but it gives us a starting place for discussions.

    The sun is up for 12 hours a day.

    The solar panel gets full sunlight for 3 hours a day and shade for 9 hours a day.

    Shade delivers 1/10 the power from the solar panel verses full sun.

    An overcast sky is 1/3 as bright as a clear sky.

    The batteries must supply power for three days of overcast skies.

    The battery charge controller and battery are 60% efficient.

    So, we will get this much of solar panel's full rated power each sunny day:
    (100% *3 /24 + 10% *9/24) * 60% = 22.5 % of rated power into the battery.

    On an overcast day we wil get 1/3 *22.5% = 7.5% of rated power into the battery.

    The sound will be played for 30 seconds every 30 minutes on average (1/60 duty cycle).

    The standby power of the sound player is 30 uA.

    The sound player draws 30 ma from a 5 volt power supply when playing back.

    The power from the audio output to the speaker is 50 mW and the output amp is 50% efficient.

    The total average power while playing will be about [(30 uA * 5 V) * 59/60] + [30 mA * 5 V +50 mW *2) /60].
    This is about 4.3 mW of average power for 24 hours a day or about 0.104 WH each day.

    I think you need a solar panel/battery charge controller:
    The controller limits charging of the battery to prevent overheating and damage.
    The charge controller also must prevent the battery from ever being deep discharged since completely draining a battery ruins it.

    Speaking of overheating, Don't forget to keep your electronics out of the sun.

    Both the solar panel and your electronics must withstand severe weather -- heat, cold, rain, wind and condensation humidity in the air along with temperature cycles.

    The forest can be a surprisingly noisy place what with the rabbits munching grass, the wind rustling leaves, birds chirping, hikers walking and talking, bears growling and hikers screaming and running from growling bears. :)

    -- Richard