Newbie with interference!

[OzWold]

Hi, Firstly what a great site – haven’t found anything on the net as good! – Secondly PLEASE HELP – I have put together a circuit that I believed would work I have 2 main problems 1: interference 2roblems with voltage oh and thirdly I know only a very little about electronics but i am getting there! I have included a circuit diagram of what I have produced. I am getting interference from my flashing LED’s & lots of noise on the mic line (like a constant buzzing drone) I believe I need to add capacitors but I have no idea where or how they work / effect the circuit. Secondly my regulators don’t seem to power the CCD cameras, from what I can tell they are supplying 5v but I don’t know how to check this properly? I know the circuit dig has a few odd components but there representations as close as I could find in my prog. If anyone can provide any suggestions I would be very grateful.

Thax Oz.

 

[Russlk]

Firstly, you need a capacitor at the bridge output, about 100uF, I think. It would not hurt to have a capacitor of 1 to 10 uF at the 78l05 output.

 

[OzWold]

Wow quick response! Thnx for your reply - I know I am dumb but I really have no idea how or why capacitors work so I guess I need to connect the one across the + & - DC side of the rectifier / Bridge (please can anyone explain what this dose and how the rating should be calculated). I managed find this: - http://www.hut.fi/Misc/Electronics/circuits/psu_5v.html
Is this how I need to wire the 78|05?

Thax Oz.

 

[Trini]

Hello OzWold,

First off your diagram is lacking some things.

As Russlk said you need a capacitor at the output of the bridge rectifier. Without this the rectifier cannot do its job.

What is happening is that the LEDs are being fed with one half cycle of the AC voltage from the power transformer secondary and they would therefore blink ON and OFF. The (filter) capacitor will make the voltage out of the Bridge Rectifier a DC voltage so that as soon as you switch the unit ON both LEDs will light up and remain ON .... no more blinking.

The regulator needs a DC voltage on its input to function properly. Since you are feeding it with feeble half cycles it cannot output the required DC to operate your CCD CAM.

Your microphone is being fed with half cycles also and not a smoothed DC . Hence the Hum or "buzzing" sound.

Yes, in theory wire the regulator as in the diagram from the link and put a filter (electrolitic) capacitor at the rectifier output. However note that a 78LO5 is only capable of supplying 100mA and therefore will not be able to operate even your CCD CAM alone muchless the microphone and LEDs also. Use a LM7805 which is good for 1 amp.

All this should solve your "interference" problem and your CCD CAM and Microphone should function OK, assuming that they are made to operate with 5 volts.

You can check your voltages with a voltmeter. The output of the rectifier should measure about 16 volts and of course there should be 5 volts out of the regulator.

Have fun!

Trini.

 

[Sebi]

If the cable is UTP, use different twisted-pair for mic. and cam. outputs.Most of case the video signal need 75ohm coaxial cable, the UTP impedance is 100ohm.

 

[OzWold]

Trini. You are a star! This explains a lot (i noticed after reading lots and lots about the rectifier that it was only 100ma DOH! << Smacks hand on head) and my flashing LED is supposed to flash (built in ic), but as you say the circuit is not receiving the power as it should be so i will give all the ideas a go and see what happens (Unfortunately it's a 30 mile drive to my local electronics store) Thanks to all the advice I have read up about smoothing capacitors - it was interesting to learn about the drop off on the down side of the cycle - one thing I would now like to find out is if there is any way of calculating what rating/type of capacitor should be used or is it down to experience? And dose anybody know a good web site where I can learn about capacitors and there types etc? It's my next step on the learning curve!

Thnx again - Wow what a site! - OzWold