If you measure the voltage from ground (black wire on both your sensor and your voltmeter) to the blue wire (in both light and darkness), what voltage do you get?
OK, I assume you mean from the black to the red wires?
No. I wrote blue because I meant blue
It was (Black to Red)-
Dark - 75.0K
But I did measure the black to the blue just in case I assumed wrong.
Light and Dark- 1.60K
Ah, perhaps I should have mentioned that you had to measure the voltage
and with the circuit powered
(+5V to the red wire and 0V(gnd) to the black wire) for the "measure the blue" I had in mind. Sorry for the confusion.
Measuring the resistance from black to red gives the series connection of the resistor and the LDR, so if we subtract the resistor from the value, we have the resistance of the LDR alone.
LDR in light: 4k2 - 1k6 = 2k6
LDR in darkness: 75k - 1k6 = 73k4
The voltage on the blue wire should then be...
In light: +5V * 1k6 / (1k6 + 2k6) = 1.9V
In darkness: +5V * 1k6 / (1k6 + 73k4) = 0.1V
Mind you, that the amount of light and darkness may be hard to repeat exactly, so if you try, your values may be somewhat different - not a problem though.
I don't know if you use A/D-C or a digital input, the latter will never see a difference and the former will probably be targeted for a higher value as well.Solution:
Swap the 1k6 resistor with a 15k resistor and you should see a change.
(You could use a trimmer potentiometer of perhaps 30k..50k if you want to dial in the exact shifting point).
Then the voltage on the blue wire should vary from around 0.8V to 4.3V under the same levels of darkness/light.
I had electrical tape on it, but removed it so that I could take a piture of it. Is that OK?
Sure, whatever keeps it from shorting.
In the long run (like when you have it all working), you'd be better off using heat shrink sleaving (HSS) though, as electricians tape has a tendency to slide over time (especially with thin single wires).
Hobby grade HSS usually shrinks to about half the diameter when heated (carefully) with a lighter at a distance underneath it.
HSS can usually be bought in a small pack with a selection diameters/sizes - or you can just get a piece of 2mm and 3mm respectively, for wiring work. When you see how it works, you'll probably want some of the larger diameters as well.
But that's just a recommendation for later. Stick to the sticky tape for now.