diff --git a/day10/day10.jl b/day10/day10.jl
new file mode 100644
index 0000000..92a491a
--- /dev/null
+++ b/day10/day10.jl
@@ -0,0 +1,63 @@
+#!/usr/bin/env julia
+
+using Test
+
+struct Instruction
+  cycles :: UInt
+  add    :: Int
+end
+
+function parse_instruction_line(line)
+  parts = split(line, limit=2)
+  if parts[1] == "noop"
+    return Instruction(1, 0)
+  elseif parts[1] == "addx"
+    return Instruction(2, parse(Int, parts[2]))
+  else
+    throw(DomainError("Unknown instruction: " * line))
+  end
+end
+
+function execute_program(io; end_cycle=220)
+  X :: Int = 1
+  cycle :: Int = 1
+  signal_strength_sum :: Int = 0
+  next_test_cycle = 20
+  for line in eachline(io)
+    if mod(cycle - 20, 40) == 0 && cycle <= end_cycle
+      println(cycle, " ", X)
+      signal_strength_sum += cycle * X
+      next_test_cycle += 40
+    end
+    inst = parse_instruction_line(line)
+    new_cycle = cycle + inst.cycles
+    if new_cycle > next_test_cycle
+      signal_strength_sum += next_test_cycle * X
+      next_test_cycle += 40
+    end
+    cycle = new_cycle
+    X += inst.add
+  end
+  println("last inst cycle ", cycle)
+  signal_strength_sum += X * sum(filter(x -> x >= cycle, 20:40:end_cycle))
+  return signal_strength_sum
+end
+
+function test()
+  @testset "signal strength sum" verbose=true begin
+    @test execute_program("example.txt") == 13140
+    @test execute_program("input.txt") == 13220
+  end
+end
+
+function main()
+  if size(ARGS, 1) == 0
+    test()
+  else
+    infile = ARGS[1]
+    println("infile = ", infile)
+    println("signal strength sum = ", execute_program(infile))
+  end
+end
+
+main()
diff --git a/day10/example.txt b/day10/example.txt
new file mode 100644
index 0000000..37ee8ee
--- /dev/null
+++ b/day10/example.txt
@@ -0,0 +1,146 @@
+addx 15
+addx -11
+addx 6
+addx -3
+addx 5
+addx -1
+addx -8
+addx 13
+addx 4
+noop
+addx -1
+addx 5
+addx -1
+addx 5
+addx -1
+addx 5
+addx -1
+addx 5
+addx -1
+addx -35
+addx 1
+addx 24
+addx -19
+addx 1
+addx 16
+addx -11
+noop
+noop
+addx 21
+addx -15
+noop
+noop
+addx -3
+addx 9
+addx 1
+addx -3
+addx 8
+addx 1
+addx 5
+noop
+noop
+noop
+noop
+noop
+addx -36
+noop
+addx 1
+addx 7
+noop
+noop
+noop
+addx 2
+addx 6
+noop
+noop
+noop
+noop
+noop
+addx 1
+noop
+noop
+addx 7
+addx 1
+noop
+addx -13
+addx 13
+addx 7
+noop
+addx 1
+addx -33
+noop
+noop
+noop
+addx 2
+noop
+noop
+noop
+addx 8
+noop
+addx -1
+addx 2
+addx 1
+noop
+addx 17
+addx -9
+addx 1
+addx 1
+addx -3
+addx 11
+noop
+noop
+addx 1
+noop
+addx 1
+noop
+noop
+addx -13
+addx -19
+addx 1
+addx 3
+addx 26
+addx -30
+addx 12
+addx -1
+addx 3
+addx 1
+noop
+noop
+noop
+addx -9
+addx 18
+addx 1
+addx 2
+noop
+noop
+addx 9
+noop
+noop
+noop
+addx -1
+addx 2
+addx -37
+addx 1
+addx 3
+noop
+addx 15
+addx -21
+addx 22
+addx -6
+addx 1
+noop
+addx 2
+addx 1
+noop
+addx -10
+noop
+noop
+addx 20
+addx 1
+addx 2
+addx 2
+addx -6
+addx -11
+noop
+noop
+noop
diff --git a/day10/input.txt b/day10/input.txt
new file mode 100644
index 0000000..734f57f
--- /dev/null
+++ b/day10/input.txt
@@ -0,0 +1,137 @@
+noop
+noop
+addx 5
+addx 3
+addx -2
+noop
+addx 5
+addx 4
+noop
+addx 3
+noop
+addx 2
+addx -17
+addx 18
+addx 3
+addx 1
+noop
+addx 5
+noop
+addx 1
+addx 2
+addx 5
+addx -40
+noop
+addx 5
+addx 2
+addx 3
+noop
+addx 2
+addx 3
+addx -2
+addx 2
+addx 2
+noop
+addx 3
+addx 5
+addx 2
+addx 3
+addx -2
+addx 2
+addx -24
+addx 31
+addx 2
+addx -33
+addx -6
+addx 5
+addx 2
+addx 3
+noop
+addx 2
+addx 3
+noop
+addx 2
+addx -1
+addx 6
+noop
+noop
+addx 1
+addx 4
+noop
+noop
+addx -15
+addx 20
+noop
+addx -23
+addx 27
+noop
+addx -35
+addx 1
+noop
+noop
+addx 5
+addx 11
+addx -10
+addx 4
+addx 1
+noop
+addx 2
+addx 2
+noop
+addx 3
+noop
+addx 3
+addx 2
+noop
+addx 3
+addx 2
+addx 11
+addx -4
+addx 2
+addx -38
+addx -1
+addx 2
+noop
+addx 3
+addx 5
+addx 2
+addx -7
+addx 8
+addx 2
+addx 2
+noop
+addx 3
+addx 5
+addx 2
+addx -25
+addx 26
+addx 2
+addx 8
+addx -1
+addx 2
+addx -2
+addx -37
+addx 5
+addx 3
+addx -1
+addx 5
+noop
+addx 22
+addx -21
+addx 2
+addx 5
+addx 2
+addx 13
+addx -12
+addx 4
+noop
+noop
+addx 5
+addx 1
+noop
+noop
+addx 2
+noop
+addx 3
+noop
+noop