LDR circuit.. no luck :(

[PhiLep]

Hi Guys, I'm hoping this is the right place to find some help.
I'm undertaking a project for school where I have to design and construct an outdoor lamp powered by solar electricity. The circuitry itself is not a big deal and I'm allowed to purchase one that is already made.

I went out and bought an "outdoor solar shed light"
(this one: http://www.jaycar.com.au/productView.asp?ID=SL2715&keywords=solar+light&form=KEYWORD).

It came with a toggle switch which I unsoldered (and melted in the process).

I thought it would be as simple as soldering an LDR in place between the red and black wires that I had removed the switch from. This didn't work for some reason. If I touch the red and black wires together the circuit is completed and the light will turn on, however if I place an LDR in between the light does not turn on. I've gone out and bought more LDRs to make sure it was not broken but none of them worked.

I have very limited knowledge on electronics and circuitry so I'm basically stuck. Does anyone have any ideas on how to make this work?

Thank you in advance
PhiLep

 

[PhiLep]

Also, I need the light to turn on when it is night time.. not the other way around.

 

[KrisBlueNZ]

You're going to need a lot more than an LDR. An LDR is not a switch, and it cannot pass the high currents your lamp will be drawing. You will need some circuitry in between the LDR and the lamp circuit.

Have a good look inside the lamp unit, and see how the solar input, the battery, and the bulb are connected, and google night light switch relay dark (or something similar). Your other option would be to buy a lamp that already has the needed circuitry in it.

You said you " have to design and construct ..." then "The circuitry itself is not a big deal and I'm allowed to purchase one that is already made". If you do that, I'm not sure what's left for you to design and construct!

 

[PhiLep]

Sorry if I was unclear, by design and construct I meant the actual base of the lamp and all of the "wood" side of it, the electronics I don't have to build myself. I'll have a search of what you suggested and hope I can figure somethig out. If I were to post pictures would you be able to guide me as to what goes where?

Thanks for your help

 

[KrisBlueNZ]

Yes, if you post some pictures I should be able to tell you what to connect to where.

You'll need a light-operated relay. Google those keywords. It's a circuit that monitors the light level using an LDR, and drives a relay that can be set to open and close at specific light levels. This relay would connect between the battery and the light, so it turns on when it's dark.

Ideally you want one with two separate brightness setpoints, so you can make sure that any light from the light bulb that gets into the LDR isn't enough to cause the relay to turn off and cause it to flash on and off!

Light operated relay circuits should be available pre-built, or in kitset form. It will need power; probably this can come directly from the battery. You need to find out the battery voltage.

 

[PhiLep]

These two wires are where there was a toggle switch:

This is where the battery pack connects:

Battery Voltage (Ni-Cd AA 600mAh 3.6v):

This is where the solar panel connects:

Solar panel connected:

The two wires touching = light is on:

Not touching = light off:

LEDs that are used:

Completely dismantled:

Closeup of the circuit board:

This is what I was trying to do with the LDR (didn't work):

And this is the lamp that I'm building. My plan was to put this lighting unit inside of the acrylic housing (white semi-circle thing) and then solder the LDR to a long wire and run it through the back of the wooden base and outside a drilled hole so that it would only detect sunlight and not the light inside the housing.

Please let me know if you need any other pictures or closeups or if anything is unclear.

 

[PhiLep]

I also looked up the light operated relays and skipping through all of the stuff I don't understand (schematics and all of that) I found this..
http://www.jaycar.com.au/productView.asp?ID=KG9090

That store is where I also bought the light from, would I be able to use this?

 

[KrisBlueNZ]

Thanks for the pictures!

Can you check that I understand this properly. The circuit board has the following connections. 1. A jack socket, for the wire from the solar panel. 2. A small connector that goes to the three-cell battery pack. 3. Two wires that go to the light. 4. A red and black pair of wires that control the light - when you short them together, the light illuminates. Right?

That Jaycar kit you found is the right idea, but it needs 12V. Your battery here is rated for 3.6V so the control circuitry needs to operate at that voltage too.

I'm not sure what the board is for. It probably doesn't control charging, and the lamp is just controlled by the switch, isn't it? So what does the board do?

It would be helpful to see some shots of the underside of the PCB, and a few more from above showing any markings on the transistors, and from different angles so parts are all clearly distinguishable. I would like to trace out the circuit diagram of that board.

I understand how you want to arrange things, with the LDR separate from the light.

 

[PhiLep]

Thanks for the pictures!

Can you check that I understand this properly. The circuit board has the following connections. 1. A jack socket, for the wire from the solar panel. 2. A small connector that goes to the three-cell battery pack. 3. Two wires that go to the light. 4. A red and black pair of wires that control the light - when you short them together, the light illuminates. Right?

That Jaycar kit you found is the right idea, but it needs 12V. Your battery here is rated for 3.6V so the control circuitry needs to operate at that voltage too.

I'm not sure what the board is for. It probably doesn't control charging, and the lamp is just controlled by the switch, isn't it? So what does the board do?

It would be helpful to see some shots of the underside of the PCB, and a few more from above showing any markings on the transistors, and from different angles so parts are all clearly distinguishable. I would like to trace out the circuit diagram of that board.

I understand how you want to arrange things, with the LDR separate from the light.

All of that is correct, the red and black pair of wires do illuminate the light when shorted.. this is where the switch originally was (which is now melted). I have no idea what the board is for, I'd assume it's just to wire everything up together?

I took some photos but I still think it might be a bit hard to see.. the tall black things are transistors (I think.. they have three legs) labelled "A1, A2, A3, A4". Then there's 8 resistors labelled R1-8. R7 has some U-shaped yellow thing soldered into the same holes. There is also some small cylinder-shaped black thing which is labelled as "D1". That's all of the components other than the battery-pack adapter socket thing and the solar panel jack socket.

There's also four holes in a row where the LED strip and the two (switch) wires are connected.

The holes are labelled as (in order): "K / L- /L+"

K = Red Switch Wire
/ = Black Switch Wire
L- = Black LED strip wire
/L+ = Red LED strip wire.

Hope that helps out if you can't read the pictures.

Here's the pictures:

 

[PhiLep]

The last photo is probably the most clear

 

[KrisBlueNZ]

That's very helpful.

Can you give the markings for each component? The transistors are the most important, but anything with letters or numbers marked on it is significant, and the coloured bands on each of the resistors would help too.

As I suspected, there's no charge control circuit. The solar panel connects through D1 (diode) straight across the battery. The rest of the board seems to be only to drive the LED array, which should only need one or two transistors (for a constant current source). I haven't figured out why there is so much circuitry on that board. A bit more info would help.

 

[KrisBlueNZ]

It seems that the circuitry on the board is just there to prevent over-discharge of the battery. When the battery voltage drops too low, the lamp is turned off. Once you give me the component markings I'll be able to confirm that this is the only function of the circuitry on the PCB.

It will be fairly easy to connect an LDR into this circuit. Would you like to put the daylight threshold adjustments in a little box along with the LDR, with a three-wire connection from that box to the lamp, or put the daylight threshold adjustments in the lamp and have a 2-wire connection to a remote LDR?

 

[PhiLep]

Hi KrisBlueNZ, here are the markings that I can see:

Transistors (all):
58050
D 331

Diode (Black Cylinder thing?):
IN5819 (or 1N5819?)
MIC


Unknown thing (Yellow U-shaped component):
103


as for the resistors, they are really small and don't have any letters or numbers on them. There are a few different ones...

Here are the colours of the stripes from left to right:

R1:
Green-Red-Black-Red-Red

R2:
Brown-Brown-Black-Red-Red

R3:
Red-Red-Black-Red-Brown

R4:
Brown-Black-Black-Red-Brown

R5:
Orange-Orange-Black-Orange-Brown

R6:
Brown-Red-Black-Blue-Green

R7
Brown-Red-Black-Black-Brown

R8:
Brown-Red-Black-Red-Red


It was difficult for me to distinguish between blue and black so some of the blue's may actually be black and vice versa, sorry.

 

[PhiLep]

and of the two options, whatever you think is the easiest option.

 

[KrisBlueNZ]

Thanks for that information. I'll upload a schematic soon.

Are you sure that all the transistors have the same marking? I would expect one of them to be different. Could you check please?

 

[PhiLep]

Oh wow I completely missed that, sorry!
I was wrong.

A1:
S8550
D 331

A2:
S8050
D 331

A3:
S8050
D 331

A4:
S8050
D 331

only A1 is different, A2 A3 and A4 appear to be the same.

Sorry about the confusion.

 

[KrisBlueNZ]

OK here's a schematic of the board that's in there, and the circuitry you need to add.

The new components are shown in the bottom part of the drawing. As you see, you'll need a few transistors, some resistors, and two trimmer potentiometers. VR1 sets the darkness detection threshold, and VR2 sets the hysteresis - that is, the deadband between the "getting darker" and "getting lighter" thresholds. Hysteresis is needed to give a positive and clean response to a gradually changing signal; without it, small changes in light intensity on the LDR would cause the light to turn on and off randomly.

You can make the circuit on a piece of stripboard. All components are readily available from Digikey or Mouser. Let me know if you need any extra info.

Edit: correction to the schematic: R11 should be 10k (not 33k).

 

[PhiLep]

I actually have no idea how to read schematics diagrams :/ I am really bad at electronics. Do you think if I show the diagram you drew to a person working at an electronics store (such as JayCar) they would be able to source all of the parts and tell me what goes where?

 

[KrisBlueNZ]

I wouldn't ask the staff at an electronic components shop. It's not their job to teach you how to build stuff. Can you find someone else at your school to help? You'll really need someone who can spend a bit of time on the project.

BTW there's a mistake in that earlier schematic - the night/day control is backwards, so it will only work in daylight! Here's a corrected version.

 

[PhiLep]

Hmm I really don't know anyone that would be able to help me put it together. The teacher was the one who told me to just put an LDR in place of a switch.. haha. I have some people in my family that are electricians, do you think they would know this stuff about circuitry?