***LDR Switch Problems***

aljamri said:

As what i do always with my friends ( beggeners like you ) i'll ask basic questions.

Which transistor have you used ECG or NTE?
how do you know the transistor and IC pin numbers ?
What is written on the relay's package and (if any) on coil it self
do you have a multimeter ( to mesure volts and resistance )

Finaly, How have you connected the Diod D1 ( the white strip side has to be connected to +ve side of the supply)

Click to expand...

Here is a list of all the components I'm using along with a link so you guys can tell me if I'm using the right stuff.

NPN Transistors (15-Pack)
https://www.radioshack.com/product/...&cp=2032058.2032230.2032279&parentPage=family

LM741CN Operational Amplifier (8-Pin Dip)
https://www.radioshack.com/product/...&cp=2032058.2032230.2032279&parentPage=family

10K-Ohm Horizontal-Style Trimmer
https://www.radioshack.com/product/...&cp=2032058.2032230.2032275&parentPage=family

1N4742A 1-Watt Zener Diode
https://www.radioshack.com/product/...D/Product+Type/Diodes&fbc=1&parentPage=family

12VDC/1A SPDT Micro Relay
https://www.radioshack.com/product/...Price/RSK/00000400/00000599&parentPage=family

I also bought a pack of LDRs I bought from RadioShack but it isn't listed on the their site. I have a cheap little meter but it does what I need it to. As far as the pin # on the parts I just refered to the picture on the back of the package it came in. The diode is contected with the line facing the + contact. I also shot it with the meter to make sure it wasn't allowing any current flow back through the diode.

spacehonkey said:

Can anyone tell me what's the difference between NPN and PNP transisotrs?

Click to expand...

'Crudely' they are mirror image versions of each other, in car terms one is positive earth, and the other negative earth.

N and P type materials are the two different kinds of semi conducting material. With an NPN transistor positive voltage/current to the base to produce current flow at the emitter and collector. With a PNP it's opposite, negative voltage/currents to the base provide current flow across the emitter collector.

I finally got the whole thing to work. I was using the wrong transistor the whole time. I was using a PNP when I should have been using NPN. Now the it works great. I need to buy a new circuit board since the one I was using has a ton of solder all over it. Thx for all the help guys.

I would like to know if any of you guys can design me a good PCB layout for this setup?

**broken link removed**

I would like to try and make my own board by using the photo-etch technique.

You could just save your time and money by using stripboard for that circuit.
If you want a neater layout there are a few utilities available.
(I have not tried these though but they look interesting):

http://www.geocities.com/stripboarddesigner/

http://veecad.com/