20W Halogen bulb viewed by a photodiode - Page 1
Forum section: electronics / general

author: StillTrying
author_rank: Super Contributor
timestamp: October 02, 2017, 12:42:48 am
content: Semi-interesting observations.Yellow is the bulb's 11.5 VAC, Purple is the relative light level.

author: MK14
author_rank: Super Contributor
timestamp: October 02, 2017, 01:29:13 am
content: As expected. The 50Hz AC, becomes 100Hz (like) because the bulb does not care about polarity.I.e. 50Hz AC, rises and falls 100 (Hz) times per second.With some kind of leading/trailing phase lag, because of the heating effect, and the light given off by the filament, as it rises/falls in temperature.It's interesting to see it happen in practice, thanks!tl;dr50Hz AC = 100Hz worth of half sine cycles (180 deg) = 100 on/off flashes per second, for filament bulbs.

author: MK14
author_rank: Super Contributor
timestamp: October 02, 2017, 01:46:36 am
content: Or in pictures:

author: StillTrying
author_rank: Super Contributor
timestamp: October 04, 2017, 03:44:55 pm
content: "With some kind of leading/trailing phase lag, because of the heating effect,"Yep, I was expecting the light peak to be at the far end of the voltage peak, but not passed it by that much. And the minimum light peak is well passed the zero volt point, - over half way towards the next voltage peak.Here's a 230V 3W LED GU10, its light output is nearly all 100Hz ripple.

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 04, 2017, 04:12:58 pm
content: Interesting experiment!I would think that the phase lag between peaks would be caused by thermal inertia. Which in turn wholly depends on the filament's thermal mass.It would be very interesting if you repeat the same experiment with a different type of (incandescent) bulb and compare the results.Simpler said than done, because incandescent bulbs are becoming harder and harder to find.

author: StillTrying
author_rank: Super Contributor
timestamp: October 04, 2017, 07:24:23 pm
content: "It would be very interesting if you repeat the same experiment with a different type of (incandescent) bulb and compare the results."Yep, I'll do a normal 240V 60W which should have a very thin filament compared with the 12V 20W halogen, I'll try to get around to a 240V 9W CFL as well. Hopefully that will be enough to satisfy mine and others' curiosity so I'll get back to doing something more useful.

author: StillTrying
author_rank: Super Contributor
timestamp: October 05, 2017, 01:13:12 am
content: The thinner filaments of the 240V 60W made almost no difference to the light delays, I even checked the mains against the 12VAC just in case, the mains phase was actually 0.5ms ahead of the 12VAC, the 20W halogen is still powered by it.The cheapo 9W CFL emits loads of EMI at 50kHz, I think a lot of the noise is actually in the light signal as putting a dark card between the bulb and photo reduces the HF noise - as well as the light.

author: StillTrying
author_rank: Super Contributor
timestamp: October 07, 2017, 01:10:26 am
content: This is what I was using, it's not very sensitive but it gives a reasonably accurate view of the shape of light pulses from DC to about 500ns, not bad for a few junk box components!

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: October 07, 2017, 02:19:08 am
content: Very interesting experiment.And deeply troubling results.Noise everywhere, eewww!

author: babysitter
author_rank: Frequent Contributor
timestamp: October 07, 2017, 09:30:14 am
content: Optical frequency doubler!

author: TerraHertz
author_rank: Super Contributor
timestamp: October 07, 2017, 11:36:27 am
content: You should add a current trace. You may be surprised by what it does at turn-on.Btw, how come the 11.5VAC ramps up over a few cycles? Not using a mechanical switch?Edit. Ah! Silly me, I know why. Current limiting transformer. Because of the current effect I'm referring to above.

author: StillTrying
author_rank: Super Contributor
timestamp: October 07, 2017, 10:38:01 pm
content: "Optical frequency doubler!"I did wonder for a minute if a photodiode viewing an incandescent had any practical use in producing a smooth low frequency sine wave, but I don't think it does. The 100Hz light shape is not a sine - just close."You should add a current trace."I'd already put in a 0.1R in and looked and measured!The 20W halogen's cold resistance seems to be about only 0.38R, from the peaks of V & I the hot resistance is 6.4R, an increase of X17 cold to hot.With only 0.38R cold resistance, adding 0.1R will reduce the peak currents, but I'll just ignore that error.The peaks of current at switch on can be as high as 8.3A, before settling to running peaks of 2.45A.The peaks of Watts at switch on can reach 80W, before settling to running peaks of 38W.Surely my measurements of this bleedin' halogen light bulb are now complete!Here's the light pulse from a cheapo photo flash gun (on low power) for a change.

author: Zero999
author_rank: Super Contributor
timestamp: October 07, 2017, 11:32:58 pm
content: A full wave rectifier and low pass filter will give a similar result.Is the lamp being powered from a low frequency or high frequency transformer? It shouldn't make any difference, since with a high frequency transformer it's modulated by the mains frequency and the high frequency element will be well above the cut-off frequency of the lamp.

author: Circlotron
author_rank: Super Contributor
timestamp: October 08, 2017, 10:10:20 am
content: You could feed the output of the photodiode amplifier into an audio amplifier and listen to the "sound" of various light sources.

author: StillTrying
author_rank: Super Contributor
timestamp: November 13, 2017, 06:23:02 pm
content: One of the attempts to detect the 20W halogen's small change in resistance with its 100Hz 12% change in light level, using the scopes V/I.There's a very slight increase in resistance(white) corresponding with the peaks in light(blue), and a slight dip in resistance corresponding with the dips in light, but that's about the best I got.

author: Red Squirrel
author_rank: Super Contributor
timestamp: November 14, 2017, 03:40:05 am
content: That is really cool, as mentioned in the other thread I had no idea incandescent (or filament based in general) bulbs even did flicker, as I figured the filament stayed lit from the heat during the lower voltage part. When you turn off a light you can actually see that it takes a few seconds for it to fully turn off. I guess it still goes down to that dim level for each cycle.Wonder if CFLs are like this too. Or neon tubes. They would probably be a much higher frequency.Going to have to play with this myself at home when I get the chance.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 14, 2017, 04:02:18 am
content: Some CFLs have a very slight "afterglow" for minutes after they're turned off. But that can only be seen in a very dark room.

author: schmitt trigger
author_rank: Super Contributor
timestamp: November 14, 2017, 01:25:40 pm
content: Indeed, all phosphors have "persistence".Which was useful when fluorescent lamps were powered with 50/60 Hz ballast, as a means to reduce flicker.Nowadays fluorescent ballasts are all high frequency.

author: SG-1
author_rank: Regular Contributor
timestamp: April 24, 2018, 04:31:18 am
content: A very cool experiment.

author: StillTrying
author_rank: Super Contributor
timestamp: May 13, 2018, 09:09:51 pm
content: Another one for the collection.Redis the light shape on brightness 1/7,greenis on brightness 5/7.

author: StillTrying
author_rank: Super Contributor
timestamp: August 05, 2018, 11:52:36 pm
content: A Philips 18W->100W Energy Saver CFL. NOS.Easier than the cheap 9W CFL - more light and less EMI.Quite low p-p light ripple, similar to the first plot atwww.derlichtpeter.de/en/light-flicker/cfd/Theblueline is the no light level.

author: StillTrying
author_rank: Super Contributor
timestamp: August 16, 2018, 08:43:28 pm
content: Short pulses through some 5mm LEDs.The Top Trace is always the detected light.RED Led 1us ~80mA pulses, - from long ago.Green Led 0.5us ~110mA,Super bright Med White Led 0.5us ~30mA, ~300X more light per mA than the standard green LED.1us,Red,Green,White,5mm.I don't know why Red LEDs usually give a more curved top light shape, I don't think it can be a photodiode thing because the top of thecurrent shapethrough the LED matches it, - curved for red and flat for green.

author: tom66
author_rank: Super Contributor
timestamp: August 16, 2018, 09:18:48 pm
content: If you have a plasma TV, you'll get some interesting effects looking at that with your photodiode.High speed video of a plasma TV:

author: StillTrying
author_rank: Super Contributor
timestamp: August 18, 2018, 04:08:39 pm
content: Quote from: tom66 on August 16, 2018, 09:18:48 pmOnly got LCDs, the photodiode + 1 transistor hasn't been sensitive enough to get a light shape from a TV or mobile phone backlight or a VFD, by the time I get it (in contact) close enough, the electronic noise is too high.

author: StillTrying
author_rank: Super Contributor
timestamp: August 20, 2018, 09:52:44 pm
content: Street lamp outside, light colour is bright creamy yellow, HP sodium I think. Drops down to near zero light in the dips.Using a big magnifying glass to get an image of the lamp's bulb onto the PD.Blue line= zero light level.

author: StillTrying
author_rank: Super Contributor
timestamp: September 22, 2018, 04:58:24 pm
content: I tried to capture the light flashes from a lightening storm, - and failed every time.Changes in the brightness of the sky were enough to move thewaiting levelup and down about 1 Div. so the lightening flashes themselves should be peaks right up the screen. In among all the electrical noise I can't see any increase in light level at all. All I can think of is that the main bright flash doesn't occur until 2-3ms after the start of the electrical noise and I missed all of them.

author: StillTrying
author_rank: Super Contributor
timestamp: May 05, 2019, 02:23:20 am
content: 1us wide 25mA pulsethrough a super bright blue 5mm LED, plenty of light, about 10cm between LED and PD.Although these are the fastestlight shaperise and fall times I've managed to get so far, I spent hours trying to improve the leading edge/rise time and failed.Is this the bestlight shapeI should expect from a SFH213 PD with -17V and 2 transistors, because further improvement of the leading edge is proving difficult.

author: StillTrying
author_rank: Super Contributor
timestamp: May 05, 2019, 02:50:40 am
content: 4us12A60V through a 100W 10x10 daylight white LED COB, 15cm and 2 sheets of thin paper between COB and PD to get the light level down.

author: soldar
author_rank: Super Contributor
timestamp: May 05, 2019, 07:40:38 am
content: Quote from: soldar on January 11, 2019, 03:24:10 pmIt was Elektor in 1979, before LEDs. See attachment.

author: Karel
author_rank: Super Contributor
timestamp: May 05, 2019, 07:58:02 am
content: I did some similar experiments using this sensor:https://www.ti.com/product/OPT101The LED lightbulbs in my house don't produce any flicker.However, we have one designer lamp that contains a LED strip and a dimmer.This lamp is really terrible when it is not set to the maximum intensity because it uses PWM at 100HzThe light produced is almost a perfect square wave between zero and maximum.The picture is from the LED bulbs that don't produce any flicker and are "safe" to use

author: Zero999
author_rank: Super Contributor
timestamp: May 05, 2019, 09:26:57 am
content: Quote from: StillTrying on May 05, 2019, 02:50:40 amFor very bright light sources, I've found it's better to skip the amplifier and connect the cathode of the photodiode, to as higher voltage it can take and the anode to the oscilloscope set to 50Ohm impedance via a piece of 50Ohm co-axial cable.Here's an oscillogram of a high power Cree® XLamp® CMA3090, driven with 60A pulses.A schematic of the driver circuit used and the photodiode with no amplifier, directly driving the oscillscope's 50Ohm input.It was discussed in another thread.https://www.eevblog.com/forum/projects/ultra-short-ultra-fast-led-flash/msg2252829/#msg2252829

author: soldar
author_rank: Super Contributor
timestamp: May 05, 2019, 09:47:53 am
content: I worked for a company that sold and installed simultaneous translation equipment for congresses. In the large venue room they would install large panels with IR LEDs which were modulated with several carriers to carry the different channels with different languages. Users would use headphones with IR receivers and could select the language/channel.In fact, I still have a couple of these IR panels with IR LEDs, waiting for a project where I could use them.It makes me think that with overhead LED lighting at home it would be possible to modulate it with audio (from TV or music) and have headphones receiving the signal. Not the most practical idea but possible. IR is better suited for this purpose.

author: StillTrying
author_rank: Super Contributor
timestamp: May 05, 2019, 02:33:12 pm
content: Quote from: Zero999 on May 05, 2019, 09:26:57 amYeah, I studied it in the other thread! Real scope shots of lineara few 1uslight pulses for comparison are very rare, I only know of 1 other, other than yours and mine, some others are current waveforms or just sims.I can't identify which PD your SFH2201 is, 4mA seems like a massive (not very linear) PD current, I'm usually only around 20-200uA.Here's one of my basicimprovementsto the "just PD and 50R" mostly to improve sensitivity.* The impedance seen by the PD is <23R.* The 510R gives X10 more signal than the PD + 50R.* No feedback cap needed.* The 15R makes it a 50R output. (I've not tried a 50R connection)* Bandwidth -1@ ~50MHz and -3@ ~100MHz.* The 0.65V emitter-collector is a bit low, and is a DC offset, but seems to work in practice.* = in theory, and/or measured in sim, results in practicemaydo vary.I've made the latest 2 TR version too small to add another stage to the 7660's -16V, I'll try inserting another -9V which would total -26V on the PD. The PD and 5k1 feedback R are already air connected to the RF TR's base, to save every 0.25pF.Most of the time I don't know if the speed/edge limits are the PD, or the best that that LED can do.

author: Zero999
author_rank: Super Contributor
timestamp: May 05, 2019, 06:23:05 pm
content: I agree 4mA is a lot, but I can assure you it's still well within the linear region of the SFH2201. I tested it by varying the distance from the emitter and it follows the square rule up to around 15mA, at which point it became non-linear. The tell tale signs of this is are a delayed turn off time and no further increase in current with intensity, similar to the storage time and emitter saturation of a BJT. Increasing the bias voltage also increased the maximum reverse current it could take before becoming non-linear. I upped the voltage to 30V, which is above the maximum rating and it would work at higher currents, but at increased dark current and reduced reliability, so isn't worth it.I did try using a high speed op-amp based transimpedance amplifier, in the hope that lowering the impedance seen by the photodiode would make it more linear, but found it wouldn't work at such high currents and didn't offer any real benefit, at such high intensities. I agree, for much lower intensities, an amplifier is necessary, but past 1mA it's generally pointless, since the oscilloscope has adequate sensitivity and 50Ohm is still low, compared to the high impedance of the photodiode.

author: StillTrying
author_rank: Super Contributor
timestamp: May 06, 2019, 06:48:25 pm
content: I'm surprised the SFH2201's typical rise and fall times are 40ns, Ishouldbe able to get 5ns PDs to be faster.Changing the reverse bias on the SHF213 PD between -9V and -27V made absolutely no difference at all to the rise and fall times orlight shape.Perhaps it's the way I'm driving the blue (or green) LED.Thegreen traceis the 3.7V directly across the legs of the blue LED, I'm not sure if the slight curve at the beginning of the 3.7V is real or not.There's lots of claims out there that LEDs can switch from fully off to fully on in 20ns, 2ns, or even instantaneous, I don't believe it myself.Should I switch to flashing an old red laser pointer.

author: Zero999
author_rank: Super Contributor
timestamp: May 07, 2019, 08:49:40 am
content: Yes, no doubt there are faster photodiodes, than the one I used, but I knew it wouldn't be the weakest link, so deemed it to be reasonable.Upping the forward voltage helps to increase the speed and I agree, the LED is probably the limiting factor. LEDs do have some capacitance, but interestingly I found it doesn't keep the LED on, probably because it discharges quickly enough. Here's an oscillogram showing the forward voltage of the LXM2-PH01-0070, a plain red LED, with a more modest current than the one I posted above. When the MOSFET turns off, the voltage quickly drops, but then it takes awhile to decay. Your circuit is push-pull, which will be faster than a single ended MOSFET drive. You could try bypassing the current limiting resistor with a small, 10pF to 100pF capacitor, to speed things up.And here's an oscillogram of the photodiode saturating, with it placed close to the LED. I didn't record which LED I used.

author: StillTrying
author_rank: Super Contributor
timestamp: May 08, 2019, 12:30:17 am
content: "You could try bypassing the current limiting resistor with a small, 10pF to 100pF capacitor, to speed things up."I had to go up to 10n across the LED's 5R to get 10ns off the rising edge of thelight shape, perhaps not too surprising with the low 5R and only a spare 0.2V above the LED voltage to play with. I'm not sure much is visible on thevoltagedirectly across the blue LED, but I've seen before that a very hard to find change of 2 or 3mV on the voltage across the LED can make a very visible change to the received light shape. I'll leave the 10n on for now.I don't want the change the 1us pulse applied to the LED too much because the original idea was to apply an as near perfect as possible 1us square pulse to the LEDs and view the differences in light shapes, especially between phosphor and non-phosphor colours.I'll probably try flashing a red laser before attempting any more improvements to the PD side.

author: Circlotron
author_rank: Super Contributor
timestamp: May 08, 2019, 12:35:58 am
content: Would be interesting to *listen* to some of those waveforms while pointing at various light sources. I wonder what the sun sounds like?

author: StillTrying
author_rank: Super Contributor
timestamp: May 08, 2019, 02:20:41 am
content: "Would be interesting to *listen* to some of those waveforms while pointing at various light sources."Many years ago I transfered audio through a torch bulb and slow LDR, similar to soldar's Reply#30, but just AM modulating the bulb. It would only transmit over about 2 feet, speech sounded muffled but perfectly understandable.From experiments in this threadhttps://www.eevblog.com/forum/projects/infrasound-sensor-what-makes-a-narrowband-2-7-hz-signal/msg1485156/#msg1485156I can convert most of what the scope can record into an audible .wav. I can't think of a very interesting light shape to listen to. Maybe a TV remote slowed down by 4 times so the 38kHz becomes 9.5kHz.

author: StillTrying
author_rank: Super Contributor
timestamp: May 09, 2019, 02:00:29 am
content: The red laser out of an old red line maker couldn't be fast flashed, there's a good regulator inside it.Greenis the current, a 400mA spike dropping to about 35mA @3V3.

author: StillTrying
author_rank: Super Contributor
timestamp: May 14, 2019, 07:46:07 pm
content: 200mA 1usthrough a 5mm superbright green LED gives a much fasterlightturn on and rise time ~19ns, I think that's the best I'm going to get, @ 200mA and 2.5% duty the green colour turns slightly bluey.It's more proof that whenused normally @ 5-20mAall LEDs turn on quite slowly, if 30-150ns counts as quite slowly!A superbright medium-warm white 5mm @25mA had the slowest turn on and offlight curvesI've seen @ ~5us long, had to increase the 1us pulse width to 10us to fit them in.Green traceis the 3V directly across the white LED.Testing complete!

author: Zero999
author_rank: Super Contributor
timestamp: May 15, 2019, 09:49:48 am
content: Yes, green LEDs shift towards blue, at higher currents.The delay in the white LED could be due to the phosphor.Here's an oscilloscope showing the phosphor lag of the LXM2-PL01-0000, a phosphor converted amber LED. I tested other LEDs, in the same range, but without the phosphor and they were much faster.https://www.lumileds.com/uploads/265/DS68-pdf

author: StillTrying
author_rank: Super Contributor
timestamp: June 15, 2019, 02:46:17 pm
content: After gettingthe lightrise and fall times down to around 18ns by over driving a superbright green LED as above, I decided that would do, because that's 10 times faster rise times than any real life LED lamp or torch I've seen.After another not very successful attempt to capture lightning flashes.After some analogue/linear stuff.www.eevblog.com/forum/beginners/floating-probe!-for-$2-50/msg1849505/#msg1849505After viewing some neons and IR remote controls.Playing with the 100W white COB including taking some 8 us @ 15 Amp photos.I've run out of LED/light experiments to do.