a little help with capacitive power supply values

[Dennis]

Hi All (Happy new year by the way :-) I hope it's a good and prosperous one for everyone!)

Melanie thanks for the clarity and tips again ,

So if we are using a 3 prong plug, (Three wire system)
then Brown wire is LIVE
and Blue is NEUTRAL
and YELLOW/GREEN is EARTH

The measured voltages are as follows
At the time I measured

Between LIVE and EARTH = 227.5 V (Readings may vary 235 to 225V (Varies based on time of day load etc) )

Between NEUTRAL and EARTH = < 1 V (May vary too!)

Between LIVE and NEUTRAL = 227.1 V

In most AC driven appliances where a mechanical SWITCH is used to switch
Either one of two switches are used (not so ?)
1.
ON-OFF
Single Pole, Single Throw = SPST

A simple on-off switch. This type can be used to switch the power supply to a circuit.

When used with mains electricity this type of switch must be in the live wire, but it is better to use a DPST switch to isolate both live and neutral.

2.
Dual ON-OFF
Double Pole, Single Throw = DPST

A pair of on-off switches which operate together (shown by the dotted line in the circuit symbol).

A DPST switch is often used to switch mains electricity because it can isolate both the live and neutral connections.

In at two wire system (2 prong plug) we are using LIVE and NEUTRAL


So....

In for the example of a PIR security light controller, the circuit draws its power from the mains , when the PIR detects a movement (PIC pin goes high) it opens the power to the load , in this instance it switches the light on (the light draws from the same mains power that the circuit draws from)
See the attached diagram..

So without creating a dangerous circuit how does one draw from the very same power that you are switching on and off (or dimming for that matter) ???

Melanie, what exactly are you suggesting to make it safe ?
You said ...

What you've got is Vdd at LIVE potential, and Vss is just -5v below it. You've put all your voltage drop in the NETURAL rail. That means your ENTIRE low-voltage PIC circuitry is actually referenced against your HIGH VOLTAGE LIVE. Yes it will work, but there is no margin for error anywhere, because GROUND is (more than) 250 volts away...

I agree it would be better to be 5V away from ground than 5v away from 250V :-)
You also said ...If you look at other half-wave rectified circuits (posted on this forum), you'll notice that Vss (0v) is sitting at NEUTRAL, with Vdd +5v above it (with all the voltage drop being done in the LIVE rail).
[/QUOTE]
What keywords did you search on ? I tried transformerless and transformer-less as well as half-wave, and didn't find very much :-(
I did find some that you had suggested to others ...
Like this onehttp://www.picbasic.co.uk/forum/atta...9&d=1213285761
and this one
http://www.picbasic.co.uk/forum/atta...1&d=1139474240

In the cuits I have seen, not many actually depict how the PIC is to be wired for various operations.

You aslo said ...

So, in that instance most of your PIC circuit is close to GROUND (since NETURAL and GROUND 'should' be connected together somewhere along the Power Grid to your Wall Socket). This makes it a damn sight 'safer' if you really want to play with mains. I use the word 'safer' cautiously - because playing with supply mains for folks that don't know what they're doing is not safe at all.

I totally agree here
But how do you suggest I change the circuit to do that ?

Please check the attached (but no yet complete) updated diagram , what's missing here is the value for R2, R3 and the TRIAC stage (I plan to use a BT139F (see attached diagram) ..Is 01A correct ?
I did raise a question about it being correct.

I do understand the risks of the circuit and have been shocked before and why I am raising all these questions is because I would like to cover all the bases and not just dive into the deep-end.

And regarding the calculations and so forth , I last used most of them 20 years ago when I was studying electronics (and sadly it is not my full-time career!) so please forgive me for being a little rusty.
Electronics and PIC programming are a really fond hobby of mine which I recently re-kindled after a nearly 4 or 5 year break !

As regards the safety aspects ... thanks to everyone who has issues warnings here and all have been noted and considered.
I have a question though .. did you all encounter the dangers first-hand by a shock or was it from a warning from others ?
Was it that feeling of total shock and frustration (at yourself) when you opened the equipment to work on or look inside while ignoring the DANGER and HIGH-VOLTAGE warning stickers ?


I look forward to your responses be they critical, analytical or other :-)

Kind regards

Dennis