blob: 216ae5a5029dc171ab98548a9de9064f5a130c9f (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
|
+-------------------+
| |
+----)------------+ |
| | | |
| +-------+ | | +---------+----o Digital output
| | | | | | |
+24V ac o---\/\/\/\/--+ | __ __ __ __ |
10K | | | | | | | | | | |
| | +--------------------------+ |
| | | | +--|(+)\ | | \
Voltage | | | | | >---+ / / Pull-up resistor
Divider | | | +--------|(-)/ | \ ~100K
| | | \ /
| | | Dual Comparator (LM 393) | \
| | +--------------------------+ |
| | |__| |__| |__| |__| |
-24V ac o-+-\/\/\/\/--+ | | |
| 1K | +---------+----o Vcc
| |
+---------------+----------------------------------------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.
|
