9V Nightlight

[securespark]

Back to my Scout project!

https://members.scouts.org.uk/documents/IET/Scouts Pack_Final.pdf

On P24 onwards, there is a nightlight project.

Am I tired, or does the circuit diagram (P25) not match the connections on the diagrams explaining how the circuit works in the light and the dark (P24)?

Apologies if I have been a fatigue-induced fool!

 

[bernardgreen]

Looks wrong to me ,

 

[mattylad]

I haven't time to look at this at the mo but if it's wrong please identify what is wrong and how to correct it - then please contact them and let them know.

 

[Nozzle]

Yes it's wrong, the emitter of the transistor needs to go the "-ve" rail on the right hand side rather than the left. Also the cathodes of the LEDs has a net missing to the -ve/.. and in fact they should be connected to the other side too.


An easier way to do is is connect the battery up the other way, put the LDR where the resistor should be, the resistor where the LDR should be, and that should work.

All in all, pretty shoddy from the IET

Nozzle

 

[securespark]

Have just been in touch with the Scouting Association. Their corporate department will be ringing me back.

Nozzle, would you say the diagram showing how the circuit operates in the dark is accurate or not?

 

[ericmark]

I ran a simulation with Multisim using a 200kΩ resistor instead of the LDR and it worked.

Using NPN transistor and all virtual components.

But I would never use a LED without some limiting resistor and the paper again and again shows an LED being connected like a bulb with no limiting resistor. Maybe the resistor is built into the LED used but that's not the way to teach.

It says an LED needs 2.4 volt well not when I was learning they were more like 1.2 volt for a RED LED it did matter what colour I used a red LED with a 7812 voltage reg to get 13.2 volt to power my CB so something I remember.

I would guess there will be a pack of components I looked at This PDF and forward max = 2.5V reverse max 5V but paper is often using a 9 volt battery which does seem wrong.