No action after PHP form Posted to SQL

I'm making a calendar of events, and the "details" for the event are on a hidden div.
I have a small icon that, when clicked, uses javascript to show the details.

What I want is that when this is clicked, the icon is replaced by a different icon (to show it is 'open') and for that icon, when clicked, to close the div again.

So the current code is

<a href="#" onclick="Effect.BlindDown('eventdetails<?php echo $event_count;?>'); return false;"><img class="open" src="./img/plus.png"></a>
 

And I'd want the image to change to "minus.png". So then it would be

<a href="#" onclick="Effect.BlindUp('eventdetails<?php echo $event_count;?>'); return false;"><img class="open" src="./img/minus.png"></a>  
 

But cant quite figure it out. Any ideas?

UPDATE

OKay, currently have from Mia, but still not working

<a href="#" onclick="toggleDisplayWait("eventdetails<?php echo $event_count;?>", "icon", 800); return false;"><img id="icon" class="open" src="./img/plus.png"></a>
 

And in the header...

    function toggleDisplayWait(divId, imgId, durationmSec) {
     if(!$(divId).visible()) {
         move = Effect.BlindDown;
         newImage = "./img/minus.png";
     }
     else {
         move = Effect.BlindUp;
         newImage = "./img/plus.png";  
     }        
     move(divId, {duration: durationmSec / 1000.0 });
     setTimeout(function() { $(imgId).src = newImage; }, durationmSec)
 }
 
 $(divId).hide();
 
     </script>
 

When I run the event, I get a syntax error on toggledisplaywait (

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