sensor light switch.

[spondootre]

Right I have made a cct using a QT113 sensor chip. I had it laid out on a breadboard with no problems using a 5v regulated supply. I wanted to utilise this in a light switch so I could replace an existing switch, so I designed the circuit and etch the board, fitted the components. Now I am having problems!! I needed to drop the 240vAC supply onboard so I have used a 240VAC - 9VAC PCB mount transformer (measures 10VAC on the multimeter). Next I have used a bridge rectifier to change from 9VAC-9VDC no problems again there it all measures fine. Next I used a regulator to drop the voltage down to 5VDC to run the chip and relay for switching the light. Again it measures 5VDC on the regulator output.

Here's the thing, there is power to the chip but no output from the chip to the transistor that switches the relay. BUT when I connected my regulated 5VDC supply that I used on the breadboard to the new circuit in place of the on board supply, the circuit works fine.

HERE'S THE BIT I REALLY DON'T UNDERSTAND
If I leave the (breadboard)supply connected but not plugged in and supply the circuit with 240VAC- TRANSFORMER - BRIDGE RECTIFIER - REGULATOR the circuit works fine, but disconnect the (breadboard) supply from the circuit and it stops working?! I am obviously missing some vital component in my circuits power supply side but what?! It is using the (breadboard) power supply for something even though it's unplugged? HELP!!!!

 

[spondootre]

OK so I am thinking I needed to add capacitors to the input/output of the regulator (0.33uF and 0.1uF) all this did was make the relay click on and off really fast, but does this mean that the problem is the supply is still messy or noisey? I am pretty useless with AC and how to get a clean DC signal which I am guessing is probably the issue, what should I do/try??

 

[spondootre]

OK so I guess i've answered my own question!! A quick check online revealed I needed a bigger electrolytic capacitor to smooth out after the bridge rectifier, it now works fine!! got to install it in the wall next!!