Need help wiring HO scale lamp posts with an LDR...

Thread Starter


Joined Dec 7, 2015
Hello, my son is in third grade and doing a science project on photoresistors and how they're used in street lights. He has a snap circuit board that shows how they work. We also found some fairly cheap model lamp posts ( that we could use to demonstrate in a model neighborhood. The thing is, I am a little confused on how to wire them all together if we were to use all 10 because I haven't seen any diagrams that show multiple LEDs with an LDR.

I've watched a few youtube videos and get the gist of it by wiring them in parallel, but I am confused on if there is supposed to be an ohm resistor after every led and just in general, how the diagram should even look with all correct values. I feel like I am in over my head as a clueless mom but I don't want to let the boy down. I just want to make sure we do it properly. Any help in the right direction would be absolutely appreciated! Thank you!


Joined Jun 22, 2012
You need a ldr switch, like this using a simple 555 timer chip, use a 6V supply.

In the circuit above, omit the relay and diode, connect your leds in its place,
Leds are polarised and will only work one way.
Note your lights dont have series resistors in them and will blow if used on voltage over 4Volts, you will need the resistors ( 330R to 1K) in series with each lamp, then you can use them on any DC voltage upto 12V.
Last edited: