From 91dcab6edcb119e252d3caa27ee70261dc71d35b Mon Sep 17 00:00:00 2001
From: AK-Homberger <53138495+AK-Homberger@users.noreply.github.com>
Date: Sat, 28 Nov 2020 10:24:31 +0100
Subject: [PATCH] Update README.md

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 README.md | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/README.md b/README.md
index 9ee6479..151f0f8 100644
--- a/README.md
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@@ -34,6 +34,11 @@ Since version 1.1 it supports now also Auto and Standby remote control. You have
 # Caution: Lighthouse III does not react on Seatalk Alarm 
 MFDs with Lighthose II will react on the Seatalk alarm function with a short beep. Unfortunately, Lighthouse III is ignoring this alarm. If you prefer to use Lighthouse III then please connect an additonal buzzer to pin 20 of the ProMicro.
 
+#Problem with some 74LS07 variants
+It seems that there are different types of 74LS07 devices available with slightly different electrical charcteristics. See issue "R3 wrong value?" for details.
+If you get a "Send Error" problem (with 12 Volt connected) then the solution is to lower the value of R3. It is important to check two voltages. With Satalk signal line high (12 Volt) the voltage on pin 3 of 74LS07 (or alternatively on cathode of D1, which is easier to measure) should be above 2 Volt. When Seatalk pulled to GND (low) the voltage on pin3 should be less than 0.8 Volt.
+
+
 # Software
 The Seatalk communication is a 9 bit serial protocol. This is not directly supported from Arduino. But I found a working 9 bit hardware serial implementation. For convenience, I have added the working source code here, because there are different versions available (in github and elsewhere).