Play/stop Button in ableton

Hello.
how do I map one button/switch on the lemur to control both play and stop in ableton? Each time the button is on i want ableton to play and each time its off i want ableton to stop playback. but i cant really figure out how to both control start and stop on the same button.

I think you can do it with custom midi but I just used a script for that:

Use a custom button, set to switch behavior
add a script, call it OnChange or whatever, select On Expression for the trigger

 ctlout(0,30+x,127,1);

will send a cc31 if the button is down and cc30 when up

hmmm, it doesn't seem to work. when i try midimap the button in ableton this message appear: The selected controller conflicts with the previous mapping to transport start. Do you want to replace the previous mapping?
Im quite new to all this scripting so perhaps i did something wrong

i tried to upload a jzlib file with the button but it seems like my computer won't let me for some reason. perhaps its attached here.

Did you remove the MIDI assignment (Target = none) ?

i just tried it. but that didn't seem to help.

here's how it looks. for some reason i can't upload it here on the forum
http://speedy.sh/eMBHs/StartStop-button.jzlib

Hi
To upload to forum -first compress the file - zip or similar . .

For the Button issue - the 30 to 31 in the controller section is for arrays of buttons
You need to either remove MIDI assign here or just deselect 'x' variable in Project pane.

Your OnChange script needs to know what is triggering it - put x in field next to execution 'On Expression' . . .x
Currently there is nothing telling it when to act . . .

Cheers
MM

U bloody legend! thnx