a little help with capacitive power supply values

[Dennis]

Hi all

Thanks to everyone for their help so far ..

Steve for the tongue-tip-test tip and for the latest one
but I am already referring to that document in post number 1 in this thread .. and that's the source of the confusuion.

Amgen thanks for the bridge-rectifier based sketch and formulae !

Dave Houston I will remain eternally grateful for the X-10 info pages and other links.

Adam those links you pointed me to where a great read and it seems I may have opened a can of worms with this thread ??

Dave, Mackrackit aka "CODE EYES" thanks for the forewarning and all the help thus far.

Melanie not only did you clear up my confusion regarding the calculation but have also given some fantastic tips to take into consideration which also triggered some more thoughts/questions.

So far I have the following calculated.

For 220V @ 50Hz to drive a MAX load of 30mA, I would need the following values (or have I messed up somewhere and is it just under 15mA?)

MOV(VDR1) = 275V
C1 = .47uF (suggested is X2 rated 275VAC based on other forums posts and internet sources)
R1 = 100 OHM (1/2 Watt)
D1 = IN4007

C2 = 470uF 25V (electrolytic)
D2 = 5V1 Zener

If all is correct, this output a half-wave rectified, smoothed 5V supply, right? If full wave were required I would need to a
If there are any further suggestions/changes I would appreciate them.

Is it true to say that the circuit ground 'hovers'(for lack of a better word) below HOT/LIVE and is not reference to EARTH GROUND and this is why all the warnings and danger signs ?

My questions are ...
(And while I ask I am busy reading/checking up on the following)

1.Whats happens when the circuit wants to draw more than max Ohms ?
2.How do I check the current draw of my PIC (assuming the PIC is standalone and not connected to anything other than power ?)
3. Once I start connectinng things like a push-button or triac or relay and perhaps an LED and maybe a POT for dimming, what would the ball-park usage start looking like and why ?
4.Which component is taking the most strain as the circuit draws current, is it C1 ?
5.Is C1 the current limiting factor of this circuit ?
6. I was thinking of using a BT139 Triac (since I have quite a few lying around), is it a good choice? I read that
7.What should the value for R3 be if I am to drive a triac ?
8. Is it feasible/possible to add a wireless TX module to the PIC circuit and if so what safegaurds (if any) like noise reduction should I put in place and where ?
9.In post #14 here amgen points out that we are looking at 0.15UF per 10MA and this seems to run true for both bride rectifier (full-wave) based as well as for the non-bridge based (half-wave) supplies. So the question is why choose to use a rectifier or not ? Is it cost ? Less of a smoke factor ? Space ?
10.To test the voltage on the output side could I just pop my good old Fluke meter on 5V and circuit GND with it set to read DC volts.
(and yes I will make sure I am insulated - rubber sole shoes, no jewellery, rubber gloves - hell I will wear a rubber suit if needs be!)
11. Are there any tips for connecting things up on the PIC side ?
12.And for taking measurements on the PIC side ? Apart from the app note SAFETY PORTION which refers to using an isolation tranformer.
Anyone have a schematic/block-diagram for measurements please?
13. Unless I am planning to use zero-crossing point to control the triac (can't think of a use right now, can you ? ) ,should I be concerned about zero-crossing issues as I have read somewhere that this circuit may cause slight delays in switching the load on or off based on Wattage and type either resistive or inductive) because the zero-crossing signal is phase shifted from the actual zero-crossing?

Oh and last but not least I can think of at least two applications that might be a no-no
1.Touch-sensitive pad(s)
2.ICSP
But what about things like USB or Connection to the PC serial port?
What sort of buffering or isolation would be required if is possible.

Apologies for the lengthy post and any questions which may seem obvious or silly to anyone reading this post (and the other posts too!)


Thanks once again

Kind regards

Dennis