AC switching with TRIAC from TTL
From: weissj@psd.gs.com (Jeffrey Weiss)

Here's a TRIAC-based solid-state relay circuit:

+5VDC
|    180                      180            2.2k
+---/\/\/\----+-----+   +----/\/\/-+--/\/\/\---+-------> 120V
              |    1|   |6         |           |         Hot
              |    +=====+         |           | MT1
              |    | MC  | TRIAC   |          +-+
              |    | 3032| Driver  |        G | | TRIAC
              |    +=====+         |         /| |
              \    2|   |4         |        / +-+
       2N3904  |----+   |          |        |  | MT2
              /     |   +--------- | -------+  |
             V      \              |        |  |
             |      /              |        \  |
             |      \ 43    .01u  ---   10k /  |
             |      /       500V  ---       \  |
             |      |              |        /  |
             +------+              |        |  |            Neutral
             |                     +--------+--+---o    o--> 120V
             /                                      load
 >-/\/\--|  2N3904
             \
              V
              |
             ---
            ///


Circuit Description

The MC3032 is an optoisolator TRIAC driver. The 180-ohm resistor sets the current for the LED emitter in the optoisolator. Change the value of this resistor - if necessary - to get reasonable current (e.g., 15 mA).

Note that you cannot test this circuit without a load. The TRIAC will not switch unless connected to an AC voltage source, so you can't test it for simple switching w/o applying AC and a load. Note the 500V rating on the .01 cap.