A message from our CEO about the future of Stack Overflow and Stack Exchange. Read now.

Hot answers tagged

18

You will be getting a narrow band, many LEDs have width of about 20 nm at 50% down from the peak; other LEDs have quite a wide band. The datasheets for LEDs will give you a curve for those specific to a particular LED. Here are the graphs of LEDs I chose for a scientific imaging project based on how narrow their bands were without resorting to exotic ...


3

Yes this is possible to implement with digital logic chips. The circuit requirements that you describe would require a state machine design that has four states, one for each of the LED on states and one for when they are all off. One possible design would use four D-type flip-flops designed to be connected into a chain to permit one flop to be set at a time ...


3

It's quite easy to do. You need to debounce the pushbutton and use it to clock a counter/decoder that drives the LEDs, eg. HC4017. Wire it to reset after the last LED. Two chips (eg.+ 74HC7002), maybe three if you want a bulletproof reset to a known state at power up. Use one ST Nor to debounce the pushbutton (with an RC and pullup and use the remaining 3 ...


3

The voltage across an LED is about 2V and stays at just about 2V. With a fixed power supply voltage it means that you have a fixed voltage across (and therefore a fixed current through) the series dropper resistor. The resistor is acting as a constant current source and its current is shared between however many LEDs you have in parallel. Lets say you ...


3

It's almost certainly an astable multivibrator, or LED flashing circuit, which is a classical circuit and one which is often a first project. Here's a tutorial on one. https://www.build-electronic-circuits.com/astable-multivibrator/ Try following the tracks on the bottom of the PCB and see if you can match it to the diagram in the tutorial I linked.


2

Look again: - I see R1 to R10.


2

It is supposed to flash the LEDs alternately. Here is a likely schematic using similar part types and values. I've made it a bit asymmetric by changing R1/R2 by +/-10% from nominal (and skipped initial condition) so it will start reliably. simulate this circuit – Schematic created using CircuitLab Below is a simulation in the Circuit lab ...


2

The WS2812 series of LEDs with built-in controllers may be a very simple solution for your application. They are most often seen on the LED strips / rolls and in that format come with a controller. Each LED is connected to positive and negative supply and a data line is fed in one side of each chip and out the other to the next chip. A string of pulses is ...


2

I am wondering why 12V is the standard voltage for LED strips (RGB/W) when each SMD LED whether it be 3535 or 5050 is usually rated for ~3V. This will be a bit long but it turns out that this standard is a natural fit for the use case of strips. 12V white LED strips use groups of 3 LEDs and a resistor in series. With 3-3.4V on each LED, this leaves 1.8-3V ...


1

Yes, you can add them in series or parallel. Series would perform best, as there is a situtation that occurs with this circuit where if the resistance is too low, the LEDs all start to glow dimly all the time. For a 9V battery application the math to choose the appropriate resistor is as follows: \$R=\frac{V}{I}\$ Now the voltage (\$V\$) is the battery ...


1

You need to reverse the orientation of the LED. Connect the anode of the LED to the output of the NOT gate, then connect the cathode to the resistor and the other end of the resistor to ground. The LED will light when the output of the NOT gate is high, which is when TX is low.


Only top voted, non community-wiki answers of a minimum length are eligible