From ad9adb3614e5cc0765bf75c43343e0d4a422c520 Mon Sep 17 00:00:00 2001
From: Astrid Smith
Date: Sun, 18 Sep 2011 20:40:48 -0700
Subject: Circuit diagram cleanup

---
 circuit.txt | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

(limited to 'circuit.txt')

diff --git a/circuit.txt b/circuit.txt
index 408f8ee..216ae5a 100644
--- a/circuit.txt
+++ b/circuit.txt
@@ -10,12 +10,20 @@
                        |   |   +--------------------------+    |
                        |   |   |   |     +--|(+)\    |    |    \
            Voltage     |   |   |   |        |    >---+   /     / Pull-up resistor
-           Divider     |   |   |   +--------|(-)/       |      \     ~10K
+           Divider     |   |   |   +--------|(-)/       |      \     ~100K
                        |   |   |                         \     /
-                       |   |   |   Comparator (NS M8830)  |    \
+                       |   |   | Dual Comparator (LM 393) |    \
                        |   |   +--------------------------+    |
                        |   |      |__|  |__|  |__|  |__|       |
 -24V ac  o-+-\/\/\/\/--+   |                         |         |
-           |    1K         |                         +---------+----o  Digital +5V
+           |    1K         |                         +---------+----o  Vcc
            |               |
-           +---------------+----------------------------------------o  Digital ground
+           +---------------+----------------------------------------o  Ground
+
+The 120Vac <-> 24Vac transformer could be replaced by a larger voltage
+divider, but that would couple the USB ground line to one pole of the
+AC line.
+
+Comparator is LM 393 or equivalent, used as a zero-crossing detector.
+
+Digital output is connected to pin B0 of the Teensy.
-- 
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