I'm about to order some parts for two projects and I have some quick questions.
The first, I am trying to make an Arduino phone connection, following the tutorial at http://brohogan.blogspot.com/2009/12/telephone-interface.html. I don't know what the parts are on the schematic from the phone connection to the DAA. Its in the top right of this schematic:
Next I'm building the dimmer circuit from herehttp://wiki.dxarts.washington.edu/groups/general/wiki/4dd69/. On the 120VAC should I be using 1/2 watt resistors?
I don't know what the parts are on the schematic from the phone connection to the DAA. Its in the top right of this schematic:
F1 & F1 are fuses. The S05K230 is a varistor, which is an over-voltage protection device. If you get a voltage spike the varistor starts conducting to short-out the voltage, and if there is enough current available, the fuses will blow, protecting both the varistor and the circuit..
On the 120VAC should I be using 1/2 watt resistors?
One way to calculate power is: Voltage squared/resistance 120*120/33,000 = 0.436 Watts. Since current only flows during the positive half-cycle, you'll dissipate half that. There is a rule-of-thumb with resistors to use a power rating of double (at least) the actual power, so 1/2W is good.
On the TRIAC side, you won't have much current flowing into the TRIACs gate, so any size resistors should be OK. (It wouldn't hurt if you want to use 1/2 Watt there too). I built a opto-isolated TRIAC driver recently, and it worked with 1/8th Watt resistors. But, I first tried wiring them directly in-line and the small resistor leads were mechanically too flimsy... I re-built the circuit on a perfboard and switched to 1/4 W resistors.
Thanks DVDdoug, that is all very helpful.
Would a .1 Amp fast fuse be fine here? And could you suggest a common varistor that would work? I believe the S05K230 is for 230 volts. Or would I be okay just using 2 fuses?