What is the recommended exposure time for presentisized positive photoresist board using UV light, fluorescent light, CFL bulb and (will it also work with LED light)?   How do we also determine if the resulting exposed board that failed is overexposed or underexposed like this?
120945
I would like to manufacture DIY PCB. I am planning to make a UV box like on , then I wonder how I can determine the best UV exposure time?   or if I use the Sun as the UV source, how I can determine the exposure time as the strength of sun light varies over the time?   What happened if the board exposed the UV light longer than it supposed to?
105310
I came into Electronics through Arduino, so pardon me if my knowledge about non-Arduino circuits is somewhat silly. I am preparing a small electronics project for my school with LDRs to detect light levels. With, an Arduino I could easily detect light levels and when they go down a threshold, I turn on a relay.   But, I wanted to make this without an Arduino, so I though of using an LM339 Comparator. I connected pin 3 of IC to Vcc and pin 12 to Ground. Pin 4 has an input lower than the input on pin 5 which receives input from Vcc. Lastly, I had the output 1 from pin 2 connected to an LED.  This circuit is only to test the comparator. If it works I am going to change the reference voltage and in place of the LED place a transistor. Here is a quick circuit Diagram I created:  But, the LED does not glow. Even if I switch the inupts, the LED does not glow. I tested this in circuits.io, the online simulator. It works perfect there. But, the problem persists on the breadboard.  How do I get the LED to glow in my circuit on the bench?  UPDATE: I just got the LED glowing with the help of Raj, but how can I connect the base of a transistor in place of the LED.
4242
I'm new in electronics. I want provide 9V (VVD9) and 5V (VCC) for my electronic board including power mosfets (IRF 3205), high power LED (14V-3.5A), micro-controller (at-mega16), and etc. I use this strategy to provide those voltages for aforementioned elements as depicted below:    For more details I provide the main part of circuit as shown below. The circuit provides strobe (5Hz-2%duty cycle) for LEDs and a Camera:    I have two questions:   Is using that strategy (shown in first image) good? As depicted in first image, input voltage is 24V. I Also use it for high power LEDs (in second image). Is there any side effect? (for example, voltage drops when LEDs are pulsing).   Any help or suggestion will be appreciated.
59555
I am trying to learn basic oscillator circuits with the help of this   But when I connected the components, my LED is not blinking. Rather, it is giving bright light.  The components I have used are 1K resistor 18V battery 200uF capacittor 2N2222 transistor and LED with 100 ohm resistance.  Here is the circuit:      From above page:
37912
I'm thinking about using  optocoupler - it has a separate lead for base of phototransistor. How do I use it? I suppose I can't leave it floating?
79116
I've only recently started taking photos and got into shooting concerts in a small venue that has neither a pit, nor proper lighting. All they use is some kind of simple LED array.  The thing is nobody wants to operate the lights and they tend to be too strong (I think).    Sometimes it's just like that for 15 mins or something... Photos seem to be out of focus, but I'm 99% sure they are (you can never be sure with a Nikon D7000, though).  These were shot using the 35mm DX and then cropped. Sometimes you can get something out of these kind of photos in LR (luminance, clarity), but it mostly looks like you f*ed up...  What can I do about it, except waiting for the light to change?   Underexposing will lead to heavier post-processing, which is unacceptable and B&amp;W looks ugly and not sharp...  Of course not every photo has to be a keeper, nonetheless I'd like to know how to deal with that.  edit to explain(...)  Not exactly a duplicate, because I'm not using aperture priority so metering problems don't apply here. Different colour of light (green) + same settings, and the photo is fine. I'm aware of light waves having different lengths, etc. Just asking whether I should underexpose or it's just the way it is.
90226
I am creating a custom box that will contain 3 * 400 watt metal halide bulbs (1200 watt total). The box will remain closed for 60 minutes, open for the next 60 minutes, then closed, then open and so on.. for a period of 10 hours. The box will open/close from the the front panel (the "door") using Arduino and Servo motors.   Since the bulbs will be generating a lot of heat I will attach a Duct Fan at 240 CFM on top of the box (is the top the best place to put it?). Something like this:   The box itself will be made out of wood so I will coat it with a heat resistant spray from the inside so it doesn't catch on fire. Something like this:   When the box is open I will need the box to emit as much light as possible. Therefore, I will coat the inside with a reflective substance (something like this: ) so all light rays are dispersed from the box..  What do you think?  Thanks
39326
I now have a PCB with 64 UV LEDs on it and I use this to expose other PCBs. I have a serial resistor for each LED which produces a lot of heat and consumes about 1.3 A at 12 V.  I am now considering to make a bigger UV unit with twice the size of my current UV unit. I have searched on the internet how to drive this amount of LEDs but the only things I came across where ways to drive each LED individually.  I was thinking to make groups of LEDs (5 by example) and use one resister for each group of LEDs.  Are any other efficient ways to drive 128 LEDs without grouping the LEDs?
33467
I have a simple circuit:    The max rating (current) of the LED is 30mA.  How can I work out what the resistance of the resistor needs to be? By using ohm's law I found it to be \$3V/0.03A = 100 \Omega\$. However using software called , and trial and error I got the minimum possible resistance to be 36&Omega;. However, if I use a 35&Omega; resistor, then the LED breaks. Is the software wrong, or (more likely) am I doing something wrong?
82060
I'm quite blank when it comes to electronics, but am trying to learn...   So I bought a  from Banggood to get some solder practice.   As you can see from , the leds will change color and turn on and off in different patterns.    question already establish that two pin RGB leds most likely contains some kind of micro chip, but it doesn't say anything about how they can be controlled.  The chip on the board is a STC15F204AE, and I guess that's the one responsible for creating the patterns. But again - how?  Is it just a fixed sequence pattern in the LED, and then the chip ensures that each LED receives power right after the previous, or is the LEDs addressable some how?
99774
I'm trying to make it so that the plane is transparent except for the light from the aqua emission. Or in other words, how can I make it so that the plane's white areas are transparent and the plane's aqua areas are not? I want to achieve this without using the compositor, only with material nodes.
20834
For blue LEDs with a forward voltage of 3.3 V and supply voltage of 3.3 V, is a series resistor still needed to limit current?  Ohm's Law in this case says 0 &Omega;, but is this correct in practice?  Perhaps just a small value like 1 or 10 &Omega; just to be safe?
22088
One of my longstanding interests is long exposure night photography.  However, many of the situations where I am shooting require exposure lengths on the order of 10 minutes, which is far beyond what the internal meter in my camera (5DII) can handle.  Right now, I take a test exposure, extrapolate from that to guess my exposure time, try again, etc...  This works, but since the test exposure alone can be 10 minutes, and it generally takes me a few shots to get the exposure right, it can take 30 minutes to an hour just to figure out exactly how long I need to expose for.  Obviously, this is really inconvenient (fortunately, long exposure subjects don't move much, most of the time).   For instance, recently I did a series of 13 minute exposures at f4, ISO125. It came out really well, but I would up spending 2 hours to get one shot.  Anyways, is there an easier way to determine how long an exposure has to be, preferably that doesn't take multiple test exposures? I've looked at light meters, but none of them make explicit statements about how low a level of light they can handle.
68221
What diode modifiers are used in practice to model LEDs with SPICE (Berkeley v.3f5)?  are available to me:  #       Name    Parameter                    Units      Default Example  Area 1       IS      Saturation current             A         1e-14   1e-14    * 2       RS      Ohmic resistance               Ω         0       10       * 3       N       Emission coefficient           -         1       1.0 4       TT      Transit-time                   s         0       0.1ns 5       CJO     Zero-bias junction capacitance F         0       2pF      * 6       VJ      Junction potential             V         1       0.6 7       M       Grading coefficient            -         0.5     0.5 8       EG      Activation energy              eV        1.11    1.11 Si                                                                  0.69 Sbd                                                                  0.67 Ge 9       XTI     Saturation-current temperature exponent  3.0     3.0 jn                                                                  2.0 Sbd 10      KF      Flicker noise coefficient      -         0 11    AF      Flicker noise exponent         -         1 12    FC      Coeff. for for.-bias dep. cap. formula   0.5 13    BV      Reverse breakdown voltage      V         ∞       40.0 14    IBV     Current at breakdown voltage   A         1.0e-3 15    TNOM    Parameter measurement temp.    °C        27      50         The dc characteristics of the diode are determined by the parameters IS and N. An ohmic resistance, RS, is included. Charge storage effects are modeled by a transit time, TT, and a nonlinear depletion layer capacitance which is determined by the parameters CJO, VJ, and M. The temperature dependence of the saturation current is defined by the parameters EG, the energy and XTI, the saturation current temperature exponent. The nominal temperature at which these parameters were measured is TNOM, which defaults to the circuit-wide value specified on the .OPTIONS control line. Reverse breakdown is modeled by an exponential increase in the reverse diode current and is determined by the parameters BV and IBV (both of which are positive numbers).   For example, using this basic, cheap red:      I don't care much about high-frequency characteristics -- just would like to be able to match it's IV-curve within its operating specs (-10uA/-5V leakage to +100mA/+2.2'ishV forward):
52352
I was trying to make a photo of my girlfriend around 9 pm with a D7000, Sigma 24-70 2.8, and SB-900. She was in the center of the frame, taking up about 20% of the frame. About 40% was taken up by ground, and the rest was the dark heavens.  I set my camera dial to A (aperture mode), aperture to f/2.8, ISO set to 400 and the SB-900 set to TTL mode. I was also experimenting with exposure (+0,7), yet all my photos had a dark background.  What can I do to expose at night without a totally black background?
90570
I'm trying to see how  correlates with practice. That answer basically says I need to let enough light into the camera and then use the highest ISO value and I'll get the lowest noise then.  So I make two shots with the same camera. Camera has aperture set to a specific value, fully manual mode, camera is on a tripod and focused onto a specific faraway object. Shooting is done around midnight, so it's rather dark. The scene is a large industrial building standing faraway across a field from the camera. The field has no light sources, all lights are on the industrial building.  I dunno if it's important but images are written as JPEG inside camera - no shooting to raw and external post-processing. Maybe that's why I see my unexpected result.  Camera highest ISO value is 3200 (not using extended ISO values).  So I first shoot with ISO 1600 and shutter speed set to 1/125 second and then I shoot with ISO 3200 and shutter speed set to 1/250 second. The amount of light should be identical and indeed both shots look properly exposed and exposed the same way.  When I open the pictures in an image viewer and zoom in to one hundred percent  I see that ISO 1600 shot is much cleaner than one with ISO 3200. I checked that several times and I'm sure - it's not the other way around.  Why is this? Is this because of post-processing difference?
68116
A friend of mine just found 3 rolls of exposed 135 (i.e. 35mm) film. They are at least 10 years old. He'd like to know if it is even worth taking them to the local hour photo lab but also if he should give them any special instructions.