diff --git a/app/src/main/java/net/thauvin/erik/android/tesremoteprogrammer/filters/NumberFilter.kt b/app/src/main/java/net/thauvin/erik/android/tesremoteprogrammer/filters/NumberFilter.kt
new file mode 100644
index 0000000..f7b45a6
--- /dev/null
+++ b/app/src/main/java/net/thauvin/erik/android/tesremoteprogrammer/filters/NumberFilter.kt
@@ -0,0 +1,57 @@
+/*
+ * NumberFilter.kt
+ *
+ * Copyright 2016 Erik C. Thauvin (erik@thauvin.net)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package net.thauvin.erik.android.tesremoteprogrammer.filters
+
+import android.text.InputFilter
+import android.text.SpannableStringBuilder
+import android.text.Spanned
+
+class NumberFilter : InputFilter {
+    private val allowed: String
+
+    constructor(allowed: String) {
+       this.allowed = allowed
+    }
+
+    override fun filter(source: CharSequence,
+                        start: Int,
+                        end: Int,
+                        dest: Spanned,
+                        dstart: Int,
+                        dend: Int): CharSequence? {
+
+        if (source is SpannableStringBuilder) {
+            for (i in end - 1 downTo start) {
+                val c = source[i]
+                if (!allowed.contains(c)) {
+                    source.delete(i, i + 1)
+                }
+            }
+            return source
+        } else {
+            val sb = StringBuilder()
+            for (i in start..end - 1) {
+                val c = source[i]
+                if (allowed.contains(c)) {
+                    sb.append(c.toUpperCase())
+                }
+            }
+            return sb.toString()
+        }
+    }
+}
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