Probably one for Mr Beeny Boy.

LDR = Light Dependant Resistor
LED = Light Emitting Diode

Do LED lights work differently in the working of an LDR than incandescent light?

I know LEDs strobe. Quicker than the human eye can detect.

However, does this “strobing” send an LDR berserk? Are LDRs that responsive that their resistance will go up/down in line with the strobing?

It’s all about the TOOTs. you see. I made this signalling system that works a beaut. (Using Picaxe processors). LDR in the middle of the track. Train goes over, ambient light goes dark. Picaxe code detects the change in resistance of the LDR and turns signal red. Train goes past, and light level resumes, wait 45 seconds and turn signal green. That’s the gist of it, but a little more complex than that.

I’ve replace the incandescent (halogen floodlights) in the train room with LED floodlights.

In short, the signals go berserk. They appear to have no idea what’s going on when under the LED lights.

Any thoughts? Google is not being very helpful.

haven’t done the experiments, note many LED are narrow spectrum though

SCIENCE said:

haven’t done the experiments, note many LED are narrow spectrum though

Haven’t done the experiments either, but light sensitive cells (I assume LDRs) are very often used with LEDs. You see them across doorways for instance, and also (unless I’ve heard wrongly) TV remotes.

Have you considered putting a capacitor in parallel with the LDR to filter out any high frequency components that could be affecting the signal?

Woodie, I don’t think I’ve ever used an LDR in my life, and certainly have no understanding of their underlying characteristics, response time, frequency dependencies etc. I hadn’t even thought about LED lights flickering and wasn’t aware that they do. Molly’s idea of a capacitor may have some merit and you may have to look into a schmitt trigger type OP amp to overcome the oscillation and give some decent hysteresis to the circuit. ‘‘btm, you’re the electronics bloke around here, your two cents?

Mr Been,

You can test the value of the LDR resistance in the Picaxe processor. You set the values to be either 0 – 64, or to 128 or 256.

Brighter the light, the less resistance. . On startup, I sample the value, and that value becomes the ambient light. I sample the value 4 times a second, and if the value drops to below 50% of the ambient light, (a train has gone over the LDR) then set the signal to red. etc etc etc. All the signals are linked, so the system passes the current signal’s status (red/yellow/green) to the previous signal. ie. Current signal = red, previous signal will be yellow and so on down the line.

Works fine in ambient room light (coming in through the doors/windows etc, or the old halogen filament lights). Turn the LED floodlights on, and Arthur’s your Martha. It all don’t know where it’s at and all the signal do a fabulous light show.Turn off the LED floodlights and all is fine again. The only thing I can think of is the LED lights “strobing”, and the LDRs are that sensitive that they’re picking up the light/dark 50 times a seconds. I can’t test the LDRs for this. Only have an analogue (needle) multimeter, and I don’t think a digital mutlimeter would pick it up either.

Oh… and if you want to see an LED strobe, just look at one in the dark, and roll you eyes round widely and quickly. Try it with some car red tail lights that are LED.

The LED floodlights are each a block of 50 LEDs. (10 * 5) and I’ve put 5 of them up so far.

sibeen said:

Woodie, I don’t think I’ve ever used an LDR in my life, and certainly have no understanding of their underlying characteristics, response time, frequency dependencies etc. I hadn’t even thought about LED lights flickering and wasn’t aware that they do. Molly’s idea of a capacitor may have some merit and you may have to look into a schmitt trigger type OP amp to overcome the oscillation and give some decent hysteresis to the circuit. ‘‘btm, you’re the electronics bloke around here, your two cents?

What kind of LDR are you using, Woodie? Are you sure it’s not a phototransistor or photodiode? How are the LED lights connected (DC or AC?) If they’re incandescent replacements from a lighting shop, there’s a switchmode power supply built into the light case, so it’s running on DC, in which case it doesn’t strobe or flicker. What colour are they? Can you be a bit more descriptive with the light sensor’s response than “go berserk”? Or is it the traffic signals that go berserk, so that the picaxe itself that seems to be confused? Are the LDRs connected to opamps at all? How big are the LDRs (eg ORP-12?) Could the LED floodlights be reflected onto the tracks through the train’s wheels, giving successive bright-dark (low-high resistance) bursts, thus confusing the picaxe? Are you able to connect an oscilloscope to the circuit to see what’s happening?

quick read, you’ll need some capacitance in your light sensor circuit (assuming it works with that spectrum of light okay) to take out the LED flicker maybe

if you post an image of the LDR with whatever resistors (or circuit diagram) etc around it and existing capacitors(if any) I might be be able to consult my genius neuron and help

I was scratching my head a bit about the strobing, btw, If fed via a smps than it’s either the worst smps ever built or something else that I’m not aware about is going on.

Change back to incandescent lights.

sibeen said:

I was scratching my head a bit about the strobing, btw, If fed via a smps than it’s either the worst smps ever built or something else that I’m not aware about is going on.

It’s possible they’re using PWM to control brightness or heat. Woodie’s last post says they’re strips of LEDs, so PWM seems more likely.

btm said:

sibeen said:

I was scratching my head a bit about the strobing, btw, If fed via a smps than it’s either the worst smps ever built or something else that I’m not aware about is going on.

It’s possible they’re using PWM to control brightness or heat. Woodie’s last post says they’re strips of LEDs, so PWM seems more likely.

Ah, good call.

btm said:

sibeen said:

Woodie, I don’t think I’ve ever used an LDR in my life, and certainly have no understanding of their underlying characteristics, response time, frequency dependencies etc. I hadn’t even thought about LED lights flickering and wasn’t aware that they do. Molly’s idea of a capacitor may have some merit and you may have to look into a schmitt trigger type OP amp to overcome the oscillation and give some decent hysteresis to the circuit. ‘‘btm, you’re the electronics bloke around here, your two cents?

What kind of LDR are you using, Woodie? Are you sure it’s not a phototransistor or photodiode? How are the LED lights connected (DC or AC?) If they’re incandescent replacements from a lighting shop, there’s a switchmode power supply built into the light case, so it’s running on DC, in which case it doesn’t strobe or flicker. What colour are they? Can you be a bit more descriptive with the light sensor’s response than “go berserk”? Or is it the traffic signals that go berserk, so that the picaxe itself that seems to be confused? Are the LDRs connected to opamps at all? How big are the LDRs (eg ORP-12?) Could the LED floodlights be reflected onto the tracks through the train’s wheels, giving successive bright-dark (low-high resistance) bursts, thus confusing the picaxe? Are you able to connect an oscilloscope to the circuit to see what’s happening?

Mr BTM.

The LED floodlights are these. They are 110 – 220 V AC. What electronics are inside them, I do not know.

The LDRs (what I call them) are these.

I haven’t programmed the Picaxe for a while. (quite a few years since I designed the whole thing). But I may recall that not only can you set the “value” to sample (0 – 62, 129, 256) there was a setting (for the LDR pins) where you could set the “sensitivity” as well.

aren’t those strip LED floods just LEDS and resistors and rely on the number of LEDs to get the correct voltage?

transition said:

quick read, you’ll need some capacitance in your light sensor circuit (assuming it works with that spectrum of light okay) to take out the LED flicker maybe

if you post an image of the LDR with whatever resistors (or circuit diagram) etc around it and existing capacitors(if any) I might be be able to consult my genius neuron and help

There are no capacitors in line with the LDRs.

sibeen said:

I was scratching my head a bit about the strobing, btw, If fed via a smps than it’s either the worst smps ever built or something else that I’m not aware about is going on.

I did the “rolling eyes” test on the LED floodlights, and they do “strobe”.

If I swap the AC feed wires around, would they strobe “opposite” to the standard wiring? ie. Swap active/neutral of the AC feed.

Woodie said:

sibeen said:

I was scratching my head a bit about the strobing, btw, If fed via a smps than it’s either the worst smps ever built or something else that I’m not aware about is going on.

I did the “rolling eyes” test on the LED floodlights, and they do “strobe”.

If I swap the AC feed wires around, would they strobe “opposite” to the standard wiring? ie. Swap active/neutral of the AC feed.

No.

Rule 303 said:

Change back to incandescent lights.

The halogen filament globes keep blowing (those long thin ones). Plus they’re 500 W each, and I have 5 of them. The LED floodlights are 50 W each.

btm said:

sibeen said:

I was scratching my head a bit about the strobing, btw, If fed via a smps than it’s either the worst smps ever built or something else that I’m not aware about is going on.

It’s possible they’re using PWM to control brightness or heat. Woodie’s last post says they’re strips of LEDs, so PWM seems more likely.

They aren’t strips. Refer previous pic. You cannot control the brightness of the LED floodlights.

Woodie said:

btm said:

sibeen said:

I was scratching my head a bit about the strobing, btw, If fed via a smps than it’s either the worst smps ever built or something else that I’m not aware about is going on.

It’s possible they’re using PWM to control brightness or heat. Woodie’s last post says they’re strips of LEDs, so PWM seems more likely.

They aren’t strips. Refer previous pic. You cannot control the brightness of the LED floodlights.

OK, that’s PWM off the table.

sibeen said:

Woodie said:

btm said:

It’s possible they’re using PWM to control brightness or heat. Woodie’s last post says they’re strips of LEDs, so PWM seems more likely.

They aren’t strips. Refer previous pic. You cannot control the brightness of the LED floodlights.

OK, that’s PWM off the table.

He’s been off the table for years. :) hehehehehe

Oh… BTW, I know what PWM is. The train loco motor’s electronics use it to vary their speed.

Woodie said:

btm said:

sibeen said:

Woodie, I don’t think I’ve ever used an LDR in my life, and certainly have no understanding of their underlying characteristics, response time, frequency dependencies etc. I hadn’t even thought about LED lights flickering and wasn’t aware that they do. Molly’s idea of a capacitor may have some merit and you may have to look into a schmitt trigger type OP amp to overcome the oscillation and give some decent hysteresis to the circuit. ‘‘btm, you’re the electronics bloke around here, your two cents?

What kind of LDR are you using, Woodie? Are you sure it’s not a phototransistor or photodiode? How are the LED lights connected (DC or AC?) If they’re incandescent replacements from a lighting shop, there’s a switchmode power supply built into the light case, so it’s running on DC, in which case it doesn’t strobe or flicker. What colour are they? Can you be a bit more descriptive with the light sensor’s response than “go berserk”? Or is it the traffic signals that go berserk, so that the picaxe itself that seems to be confused? Are the LDRs connected to opamps at all? How big are the LDRs (eg ORP-12?) Could the LED floodlights be reflected onto the tracks through the train’s wheels, giving successive bright-dark (low-high resistance) bursts, thus confusing the picaxe? Are you able to connect an oscilloscope to the circuit to see what’s happening?

Mr BTM.

The LED floodlights are these. They are 110 – 220 V AC. What electronics are inside them, I do not know.

The LDRs (what I call them) are these.

I haven’t programmed the Picaxe for a while. (quite a few years since I designed the whole thing). But I may recall that not only can you set the “value” to sample (0 – 62, 129, 256) there was a setting (for the LDR pins) where you could set the “sensitivity” as well.

you sure of those voltages?

I see this one is 220-240v

https://www.gearbest.com/led-flood-lights/pp_3008391572655437.html

ChrispenEvan said:

Woodie said:

btm said:

What kind of LDR are you using, Woodie? Are you sure it’s not a phototransistor or photodiode? How are the LED lights connected (DC or AC?) If they’re incandescent replacements from a lighting shop, there’s a switchmode power supply built into the light case, so it’s running on DC, in which case it doesn’t strobe or flicker. What colour are they? Can you be a bit more descriptive with the light sensor’s response than “go berserk”? Or is it the traffic signals that go berserk, so that the picaxe itself that seems to be confused? Are the LDRs connected to opamps at all? How big are the LDRs (eg ORP-12?) Could the LED floodlights be reflected onto the tracks through the train’s wheels, giving successive bright-dark (low-high resistance) bursts, thus confusing the picaxe? Are you able to connect an oscilloscope to the circuit to see what’s happening?

Mr BTM.

The LED floodlights are these. They are 110 – 220 V AC. What electronics are inside them, I do not know.

The LDRs (what I call them) are these.

I haven’t programmed the Picaxe for a while. (quite a few years since I designed the whole thing). But I may recall that not only can you set the “value” to sample (0 – 62, 129, 256) there was a setting (for the LDR pins) where you could set the “sensitivity” as well.

you sure of those voltages?

I see this one is 220-240v

https://www.gearbest.com/led-flood-lights/pp_3008391572655437.html

These are the actual ones I got off Ebay.

here

It says “AC175 – 265V” on the box and the label on them.

Woodie said:

transition said:

quick read, you’ll need some capacitance in your light sensor circuit (assuming it works with that spectrum of light okay) to take out the LED flicker maybe

if you post an image of the LDR with whatever resistors (or circuit diagram) etc around it and existing capacitors(if any) I might be be able to consult my genius neuron and help

There are no capacitors in line with the LDRs.

without going back and reading properly

it could be as dumb as needing just a capacitor tied in, i’ve given you a pink one, my favorite color

or may need a resistor as well

if the light level is too low because of the band (LED spectrum of light/sensitivity of LDR), you may need to do more

Woodie said:

ChrispenEvan said:

Woodie said:

Mr BTM.

The LED floodlights are these. They are 110 – 220 V AC. What electronics are inside them, I do not know.

The LDRs (what I call them) are these.

I haven’t programmed the Picaxe for a while. (quite a few years since I designed the whole thing). But I may recall that not only can you set the “value” to sample (0 – 62, 129, 256) there was a setting (for the LDR pins) where you could set the “sensitivity” as well.

you sure of those voltages?

I see this one is 220-240v

https://www.gearbest.com/led-flood-lights/pp_3008391572655437.html

These are the actual ones I got off Ebay.

here

It says “AC175 – 265V” on the box and the label on them.

says 220V in the specs.

ChrispenEvan said:

Woodie said:

ChrispenEvan said:

you sure of those voltages?

I see this one is 220-240v

https://www.gearbest.com/led-flood-lights/pp_3008391572655437.html

These are the actual ones I got off Ebay.

here

It says “AC175 – 265V” on the box and the label on them.

says 220V in the specs.

Which is what I’ve wired them into anyway.

transition said:

Woodie said:

transition said:

quick read, you’ll need some capacitance in your light sensor circuit (assuming it works with that spectrum of light okay) to take out the LED flicker maybe

if you post an image of the LDR with whatever resistors (or circuit diagram) etc around it and existing capacitors(if any) I might be be able to consult my genius neuron and help

There are no capacitors in line with the LDRs.

without going back and reading properly

it could be as dumb as needing just a capacitor tied in, i’ve given you a pink one, my favorite color

or may need a resistor as well

if the light level is too low because of the band (LED spectrum of light/sensitivity of LDR), you may need to do more

If the light spectrum of the LED floodlights is very narrow, too narrow for the LDR, then the LDRs wouldn’t work at all, would they? ie. They’d think it was dark, and that’s that.

Woodie said:

transition said:

Woodie said:

There are no capacitors in line with the LDRs.

without going back and reading properly

it could be as dumb as needing just a capacitor tied in, i’ve given you a pink one, my favorite color

or may need a resistor as well

if the light level is too low because of the band (LED spectrum of light/sensitivity of LDR), you may need to do more

If the light spectrum of the LED floodlights is very narrow, too narrow for the LDR, then the LDRs wouldn’t work at all, would they? ie. They’d think it was dark, and that’s that.

depends if it’s running on some threshold, crossing it

but just guessing LDRs have quite a fast response time, you’ve added a noisy light, so you need give the LDR some persistence like your eyes have got, easiest way to do that is to add a capacitor, probably straight across the LDR may do it, depending on current going through it and how firm or soft the supply is to it

Google hasn’t been much help. All it tells me is how to use an LDR to turn an LED on/off using Arduino or Picaxe. Can’t find anything about USING LED lights with an LDR. Much appreciated if anyone can find out, via their channels or point me in a direction where I can find out.

Nie nies.

transition said:

depends if it’s running on some threshold, crossing it

but just guessing LDRs have quite a fast response time, you’ve added a noisy light, so you need give the LDR some persistence like your eyes have got, easiest way to do that is to add a capacitor, probably straight across the LDR may do it, depending on current going through it and how firm or soft the supply is to it

Exactly Mr Sition. And I cannot find out what the LDR response time is. And yes, a “strobing” LED would be a very “noisy” light as you put it.

“Response time of 2 – 50 ms. (Much slower than photo-transistors.)”

Oh dear. I’m nackered if that is the case.

http://lednique.com/opto-isolators-2/light-dependent-resistor-ldr/

I wonder how fast the Picaxe is when it’s sampling the LDR resistance.

sibeen said:

Woodie said:

btm said:

It’s possible they’re using PWM to control brightness or heat. Woodie’s last post says they’re strips of LEDs, so PWM seems more likely.

They aren’t strips. Refer previous pic. You cannot control the brightness of the LED floodlights.

OK, that’s PWM off the table.

led light sources without brightness control might well just use a preset PWM – it has a preset light source that uses PWM so it doesn’t burn out the LED

your picaxe / microcontroller input might very very function much better if its input is grounded via a 10Kohm resistor.

what happens is that without grounding you get spurious voltages happening caused by static or similar

input pins to things like microcontrollers need to be grounded via a 10Kohm so that the digital input or analog signal is either 1 or 0

1 : use an arduino – picaxe is defunct and problem laden technology

2 grounding the input to the LDR input with a 10kOHM resistor will create a much cleaner and reliable voltage on the input pin

i’ve discovered that even going near a free hanging input pin with plastic clothing will provoke a change at an input pin because the static from the clothing will cause a change at the pin

wookiemeister said:

your picaxe / microcontroller input might very very function much better if its input is grounded via a 10Kohm resistor.

what happens is that without grounding you get spurious voltages happening caused by static or similar

input pins to things like microcontrollers need to be grounded via a 10Kohm so that the digital input or analog signal is either 1 or 0

1 : use an arduino – picaxe is defunct and problem laden technology

2 grounding the input to the LDR input with a 10kOHM resistor will create a much cleaner and reliable voltage on the input pin

i’ve discovered that even going near a free hanging input pin with plastic clothing will provoke a change at an input pin because the static from the clothing will cause a change at the pin

yeah cmos inputs may need a dampener, pulling up or down, whatever, keep it where meant to be against noise on the line, and any length is like an antenna

wookiemeister said:

your picaxe / microcontroller input might very very function much better if its input is grounded via a 10Kohm resistor.

what happens is that without grounding you get spurious voltages happening caused by static or similar

input pins to things like microcontrollers need to be grounded via a 10Kohm so that the digital input or analog signal is either 1 or 0

1 : use an arduino – picaxe is defunct and problem laden technology

2 grounding the input to the LDR input with a 10kOHM resistor will create a much cleaner and reliable voltage on the input pin

i’ve discovered that even going near a free hanging input pin with plastic clothing will provoke a change at an input pin because the static from the clothing will cause a change at the pin

Each input pin is grounded using a resistor, as the specs say to do. This ensure the pin is “pulled to ground” and works correctly when activated.

Mr Meister and Mr Sition,

You need to remember the circuitry works perfectly, and has done for years under any source of light other than these LED lights. (See above). Even low light levels. I calibrate the system, by taking the ambient light value on the LDR pin and set that as “ambient light”. When that value drops to 50% of the “ambient” light, that means a train has passed over the LDR. This allows the system to work in varying light levels. If I picked a fixed light level to determine if a train has passed over, a low level of ambient light might already be below that level. This allows teh sytem to work with just a 60W incandescent globe in the room (simlulates late evening), or high levels of daylight/floodlight.

What I need to do (I think) is “smooth” out the current being passed through the LDR, which from what I can find, has a very quick response rate to light. Causing the value on the LDR pin to vary widely and rapidly.

I have a question which sort of belongs in this thread…

I’m trying to get an old Lego train set working but the 10V AC transformer is cactus. The controller is marked 9V AC. Apparently it’s circuitry converts the input to DC.

Should I be fine to use a12V DC transformer?

Ian said:

I have a question which sort of belongs in this thread…

I’m trying to get an old Lego train set working but the 10V AC transformer is cactus. The controller is marked 9V AC. Apparently it’s circuitry converts the input to DC.

Should I be fine to use a12V DC transformer?

No, no, no, not without knowing quite a bit more. Does the controller have a transformer at its input? If it is just a bridge rectifier at the input, without a transformer, then it will probably be OK. If there is a transformer definitely don’t do it.

https://bricks.stackexchange.com/questions/2898/what-is-the-correct-input-voltage-for-the-9v-lego-train-speed-regulator

This describes a very similar controller.. see a few posts down

Ian said:

https://bricks.stackexchange.com/questions/2898/what-is-the-correct-input-voltage-for-the-9v-lego-train-speed-regulator

This describes a very similar controller.. see a few posts down

OK, you should be good. There’s no transformer so the controller can take an AC or DC input.

sibeen said:

Ian said:

https://bricks.stackexchange.com/questions/2898/what-is-the-correct-input-voltage-for-the-9v-lego-train-speed-regulator

This describes a very similar controller.. see a few posts down

OK, you should be good. There’s no transformer so the controller can take an AC or DC input.

Yeah, that’s how I figured. Cheers