Many begineers do not understand the concept of "bandwidth" or "response time" of a sensor, untill they are shown a practical experiment like yours. Thank for for the video.
You were unfair to the phototransistor. That 100k resistor at the emitter... A huge time constant! Even to the photodiode: 2k2 it's also a big resistance for them. The transistor could perform better with less resistance at its emitter. For sure...
I have a photo device removed from an old camera. It generates a mv signal when exposed to light. Do you know how I can tell which it is (Photodiode, Phototransistor, Photoresistor)?
Very nice analysis, thank you! If you didn't mind the wiring effort, perhaps you could even tack an antenna, a flat coil, to the flash housing, pick up the EM pulse, and use it as the trigger, catching the flash "before it happens", and give yourself 3 microseconds more time to react. Then again, shutter speed is counted in milliseconds, not microseconds, but hey, "good enough" never prevented anyone from wanting to do "even better", now did it?
A perfect video on a needed subject. 5 stars. I was already subscribed. Thank you. Showing the delay times and voltage ranges on each of the 3 devices was super informative. This was a really great video.
For all who do not want to waste 6 minutes of time (like me), here is: 0:29 - schematic 6:07 - probe colors, rise time 7:27 - fall time The conclusion is that the opening of the photo-element is much faster that his closing.
Hi, I am just starting to learn about electronics. So if a photodiode is better to detect fast flashes, what are photoresistors and phototransistors better used for? Also, I see the phototransistor reaches a max. intensity, stays flat, and then falls. Does this mean the phototransistor was saturated and that horizontal line is its upper limit? This is really cool, thank you for your video!
Photoresistors are non-polar and generally quite robust, so can be used in applications where those are important, although they are very slow. Phototransistors are quite sensitive and moderately fast, so are useful in general purpose applications without needing further amplification. Photodiodes are less sensitive but fast, so are used along with further amplification where speed of response is important. The phototransistor in the video is definitely in saturation, especially as it's being used with a 100K resistor. Normally, you'd use a much smaller value.
What caused the super earlly decline in the photoresistor? I get that it's slow, both up and down, but it seemed to really jump the gun on the release of the flash, relative to the other devices. Obviously the original intent is dead and done, but instead of doubting the PR, I'd say that there's something to be said about it's early decrease in conductivity, relative to it's faster counterparts..
I found your video very very interesting, as I am doing a project, where I am doing a sort of solar tracker. It is more like tracker that will track toward the point of maximum light intensity. Originally, I was going to use LDR, but is there a point in using photodiode as it appears to have superior response time? Thanks.
watch.firefly hello, can you inform me about what you decided to choose? I am building a solar tracker too and I had the exact same question as yours. Would be really helpful if you told me about your experience! Thanks
Does the sun move across the entire sky in 1 millisecond? If the answer is no, then the response difference between these don't matter for your application
neat! im only half way through. which devices did you use? im trying to figure out if i can use this phototransistor or a photodiode. kinda trying to build a transimpedence amplifier. and getting nowhere. im wondering if i burnt my components. i havent had near the performance you have had. which components ya got?
Thank you. I did not know about photodiodes. I was certain that a phototransistor would be better than a photoresistor, but I didn't know why. This explains the three nicely.
You can reverse bias the PD but it would increase dark current. Also, be careful not to exceed the maximum reverse voltage. Normally, light current from the PD can be amplified by a transimpedance amplifier.
What kind of photodiode and LED should i select for high speed data transfer? Should i select the components with the lowest rise times or are other specs important too?
Trying to figure out where to buy a photosensor which is already in a housing that I can use along side an oscilloscope to measure a monitors pixel response time, aka changing from one color to another. apparently this is how testing is done online for gaming monitors and I want to be able to test my own monitor without relying on a review (since one of my monitors is a little older and doesn't even have an in-depth review). the oscilloscope is pretty cheap, about 300 bucks. I just need a photosensor that can hook up to the BNC plug so I can use it for measurement. Which of these 3 would be fastest for measuring response time to the fastest degree? And is there a product that is already in a housing with a BNC connection to easily attach it to the oscilloscope? thanks in advance. IF they dont have anything premade, is it possible to put the best of the 3 into a housing that can sit flush with a monitor screen to check pixel response times?
If you haven't already found this, you can search for "mounted photodiodes" to see the range of what is available. usually, you will want to amplify the signal from the photodiode with a transimpedance amplifier, but you might be lucky and have a 'scope sensitive enough to read the signal from the photodiode directly.
@@RexxSchneider i did. Lmao mad old. I ended up buying a thorlabs sm05 whatever with 15ns rise/fall time and its been epic for measuing monitor response times. Tested the new alienware 3423dw and sure enough sub 1ms full pixel response which makes me think that modern reviewers don't have fast enough tools
N T Voltage? You misunderstood how it works. It outputs current, not voltage! The current to light graph is given in the data sheet. However, you want voltage - you need a current to voltage converter. A transimpedance op amp is amazing at this.
Crazy Phil I'm not sure that I understand his question... but what I don't know is do any of these things output a voltage when light is applied to it, kind of like a photovoltaic cell... I have been searching for a video where someone actually measured to see if they produce a current but so far I haven't found anything on that topic...
@@PeterMilanovski A semiconductor junction when reverse biased will conduct if photons of the right energy strike it because the light generates charge carriers in the semiconductor. So you apply a reverse bias to a photodiode and it will give a small current when illuminated. That small current can pass through a resistor and be measured as a voltage. this can happen very quickly because there is very little capacitance in a reverse biased diode. Also, a transistor with its base disconnected will not conduct, but light striking the base-emitter junction can generate charge carriers that provide a small base-emitter current, which then creates a larger collector-emitter current by the usual transistor action. The phototransistor therefore amplifies the current compared to the photodiode. Again you can arrange for the current passing though the transistor to pass through a resistor and that can be measured as a voltage. The phototransistor has a larger capacitance across its b-e junction than the capacitance in the reverse-biased photodiode, so in simplistic terms that slows down its response compared to the photodiode. It's worth noting that a photodiode can also be used without biasing in its photovoltaic mode, which increases sensitivity but results in a greater junction capacitance and hence worsens its response speed. In all cases, it is common to use an operational amplifier to magnify the small signals from the photodiodes, and I'm pretty certain you can find lots of examples of that on the internet.
@@RexxSchneider what do you mean 'the light generated the charge?' a charge is energy and energy can't be created nor destroyed..... Where is this energy coming from?
@@PeterMilanovski Light is energy. An electric charge is not. More specifically, a photon of light can impart its energy to a semiconductor by moving an electron out of its fixed place in the crystal lattice into a higher energy state where it is mobile. The electron will then move towards a more positive region. The gap left in the structure also behaves as a charge carrier (called a hole) and will tend to drift towards a more negative region. The movement of charge carriers constitutes an electric current and is the reason why a current is generated when light strikes the junction. Hope that clarifies it for you.
At 0:29 the schematic shows the photodiode as BPW34S and the phototransistor as PT334-6C. Both have datasheets readily available online, and are cheap and available from a variety of suppliers.
how did you get a high enough output from the photodiode in order to be able to read it on the oscillscope, I tried your experiment but the photodiode output is so low in order of 300mV, so the oscillscope can't read it so, any ideas about how to solve this?
It's an oscilloscope, so he's measuring voltage. Of course, if you measure voltage across a known resistance, you are equivalently measuring the current through it.
Very interesting. So you basically suggest photodiodes (or phototransistors for a higher current). Any cheap/fast model you can suggest? I am looking for a sensor in the order of 100 microsecs of rise/fall time.
I'm currently searching for really fast and affordable components and so far, PD204-6C which can be found on ebay has a fall and rise time of 10 nanoseconds. So there you go, that should be enough for your project and mine aswell. :)
Do you think you will be able to appreciate the difference? Are you using it for communications? Btw atm I can't access my order from phone. Will do in a few days but I remember it was of family Osram SFH probably 203 or 302 can't really remember on top of my head
