# Advice on Telephone Circuit

Discussion in 'Electronic Basics' started by Andrew Holme, Dec 15, 2004.

1. ### Andrew HolmeGuest

Yes, 250V would be fine.
Yes, 1000uF 16V is fine.
Right again.
The resistance of the LDR is not fixed! It varies with the incident light
level. It is quoted at one or more specific light levels (measured in lux).
As a guide, bright lighting for a workshop is about 2000 LUX. You want one
that is around 5k in ambient light and more than 100k in darkness. They
generally have very high dark resistance so you shouldn't have any problem
at that end of the scale.

2. ### DiefenbakerGuest

Im looking at building the Smart Phone Light.
http://www.electronic-circuits-diagrams.com//telephonesimages/12.gif

If anyone could answer a couple of questions.

I have tried to buy (C1) 1.u 400v Capacitor. But my local guys dont have
anything like this. Could I use something else. I did see 1u 250v but 400v
seems a little excessive, acept for spikes I suppose but I think everything
would go if it got that high.

Secondly I'm asuming that the (C3) +1000 could be a 16v cap.

Third the Relay I guess needs to be 5v relay. The diagram smudges the
number. But asuming that the trigering voltage there is 5v DC.

Finally, the circuit calls for
"A light dependent resistance (LDR), with about 5 kilo-ohms resistance in
the ambient light and greather than 100 kilo-ohms in darkness"

I have never bought LDR's it looks like you buy them based on ohms eg 100
ohms, since they are a resister. But I dont know what size to buy. Should I
get a 5k ohm or 100k ohm. Im not sure I know what to ask for?

One or any of the questions answered would be helpfull.

Thanks.

3. ### Andrew HolmeGuest

I found the following data on the ORP12:

@ 10,000 lux 80Ohms.
@ 50 lux 6kOhms.
Dark resistance (min.): 1MOhms.

That sounds about right for your application.

4. ### DiefenbakerGuest

Wow Thanks Andrew. Great info.

A clarification on the LDR. I see a ORP12 Part Number seems to be common.
Do you know whether that would be an apropriate part for this project.

One place I saw, the following comments on the Orp12
a.. Darkness: maximum resistance, about 1M.
b.. Very bright light: minimum resistance, about 100.
As you said the dark side is less of an issue. I note that it says very
bright light so this may be ok in dusk to dawn times or if the circuit more
likely is in a house where the light will not be bright but indirect.

Regards

5. ### DiefenbakerGuest

Thanks Andrew.