How to make an infinite loop say a raw JSON message once?

I have a simpler solution. Look at the image below:

I thought of a simpler contraption of what your confused Of. Radius AND powering it only once. The Repeating Command block is where you will put the radius. Like /testfor @p[r=1] Which means If You Step ontop of the command block. It will power the comparator. then in runs itno the block of your choice. Then powers the repeater. And Powers the command block at the bottom that has the Tellraw command. For Example I Used:

/tellraw @a {"text":"Hello","color":"green","default":true}. 

the comand block on the right however. Has a setblock command. You write down the coordinates of the repeater I suggest LOOKING DOWN to it. When you got it, You Do This:

/setblock {coordinates} minecraft:air 

when you power the repeating command block. It Will power the tellraw, then it will get rid of the repeater. then it dosen't power anymore. You Put repeaters on the way to the setblock command so that the tellraw command will power first. I hope You understand! :)