I am always deliberating wether to use a mechanical relay or a solidstate relay.
Solidstate relays used to be relatively expensive, and thus people constructed them from opto couplers and triacs, but there are some cheap SSR chips available. One of my favorites is the 39MF22 that is available for 1.80 euro. So I made a choice to build a solid state relay for my project.
I have to add though that a four channel relay board, ready made, is also not that expensive. So, before you build my solid state relay you may want to check out these options: http://dx.com/p/arduino-4-channel-5v-relay-module-expansion-board-137109 or even cheaper: https://dx.com/p/5v-4-channel-high-level-trigger-relay-module-for-arduino-red-157213 . In fact, these may even be slightly less expensive than the Solid state relay board I will be describing here.
Bill of materials:
4x 39MF22 from e.g. dickbest I believe it can switch 900 mA which is sufficient for most of my applications You could also use PR26MF12. It is pin compatible and switches 600 mA
4x 8 pins dil IC holder
4x LED in color of choice
4x 330 Ohm resistors
4x 2 pins screwconnector
1x 5 pins female header
1x 5 pins male header 90degrees
1x Tic-Tac peppermint dispenser The bigger one: 8.5x2x5 cm
1x piece of PCB 6x4.6 cm
For a snubber:
1x 100 Ohm resistor
1x 100 nF 600 V resistor
OK Stop right here. This circuit is meant to switch AC loads of 110 or 220 Volt. These voltages can and will kill you, so be careful and if you do not feel confident you know what you are doing, you should only use this for low AC voltage loads.
Also, as said, this circuit is for switching AC, it is not for DC. for switching DC a HCT4066 should be considered (depending on the load to be switched) or a mechanical relay