From c548958f6ebbf372e3771e8a9012a5faab34d73b Mon Sep 17 00:00:00 2001
From: StanJ <53401742+Tech-TX@users.noreply.github.com>
Date: Sat, 4 Apr 2020 11:47:54 -0500
Subject: [PATCH] Tone limit 20KHz  (#7179)

Set Tone maximum frequency to 20KHz (was 5KHz)
---
 cores/esp8266/Tone.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/cores/esp8266/Tone.cpp b/cores/esp8266/Tone.cpp
index 35a5a4151..0a156fe21 100644
--- a/cores/esp8266/Tone.cpp
+++ b/cores/esp8266/Tone.cpp
@@ -35,8 +35,8 @@ static void _startTone(uint8_t _pin, uint32_t high, uint32_t low, unsigned long
 
   pinMode(_pin, OUTPUT);
 
-  high = std::max(high, (uint32_t)100);
-  low = std::max(low, (uint32_t)100);
+  high = std::max(high, (uint32_t)25);  // new 20KHz maximum tone frequency,
+  low = std::max(low, (uint32_t)25);   // (25us high + 25us low period = 20KHz)
 
   if (startWaveform(_pin, high, low, (uint32_t) duration * 1000)) {
     _toneMap |= 1 << _pin;