[Lua] Too long without yielding and coding help.

So, I've been trying to make a code that receives a pulse of redstone from the back and then pulses front for 28 seconds then resets. But it says too long without yielding
Heres my code:

while true do
local coins = redstone.getInput("back")
if coins == true then
rs.setOutput("front", true)
sleep(28)
rs.setOutput("front", false)
local coins = false
end
end

Any solution, if yes please respond with a code!

So, your code only really needs to run through the loop every time a redstone input changes. You could throw an os.pullEvent("redstone") at the beginning. A working version that replicates the behavior of the above code would be:

while true do
  while rs.getInput("back") do
    rs.setOutput("front", true)
    sleep(28)
  end
  rs.setOutput("front", false)
  os.pullEvent("redstone")
end

Of course, I don't think that that's entirely what you want it to do, but fixing the behavior of the code is an exercise left to the reader.

One more thing, if there are multiple redstone inputs, can the time be extended maybe like sleep(tokens*28)

Say you defined a variable as 0, eg "sleepTime", every time the loop repeats. For each input that's active, you add 28 to it. After checking each input, if the variable is more than 0 you enable the output and run "sleep(sleepTime)".