# Tag Info

Accepted

### IR Blaster Resistor Calculation for IR LED (breaking ohm's law?)

The simple answer is, the LED isn't driven with 254mA DC, it's driven with pulses of 254mA. And as the LED datasheet says, it can handle pulses of 1A, when individual ulses are less than 100us, and ...
• 159k

### IR Blaster Resistor Calculation for IR LED (breaking ohm's law?)

The LED isn't driven continuously. It is driven with a 'carrier' (typically 38 kHz) that is lower duty cycle. The LED can tolerate higher currents when pulsed this way. 250 mA peak isn't unreasonable ...
• 55k
1 vote

### How do I light an LED on a ground signal when I don't have enough voltage left after the PNP?

Another variation to add to the pile: we can use a MOSFET as a crude differential amplifier, i.e. it remains off until Vg is below Vs, and then turns on incrementally from there. By setting the source ...
• 39.6k
Accepted

### How do I light an LED on a ground signal when I don't have enough voltage left after the PNP?

As pointed out in the comments (Thanks, Tim), the original circuit will not work; the transistor isn't properly biased. So to save face, here are three additional circuits that will work: I'm not ...
• 4,963

### How do I light an LED on a ground signal when I don't have enough voltage left after the PNP?

My understanding is can't modify the control signal PTT circuit, and LED should be ON when PTT control active (low), OFF when PTT not active (weak pulled to was 12V, now 6.5V). A good option is diode ...
• 335
1 vote

### How do I light an LED on a ground signal when I don't have enough voltage left after the PNP?

Firstly, I doubt your circuit would produce $V_{BE}=-5.8V$. I suspect your transistor is damaged, isn't what you think it is, or is wrongly connected. With such a small resistance at the base, most ...
• 39k
Accepted

### Can a voltage higher than LED maximum be used when using constant-current LED driver?

The sink driver requires 0.8V to get guaranteed output current, so for 2.9V maximum Vf LEDs you should have 3.7V supply voltage minimum. It won't hurt the LEDs but you might not get full current or it ...
• 407k
1 vote
Accepted

### Circuit schema 2 ways WS2812 connect with 1 PCB layout

Your updated schematic would work if "jumpered" correctly: Left-to-right: or Rigth-to-left But I seriously fail to see a benefit of this design, instead of simply "rotating" the ...
• 4,501
Accepted

### Can't get 4017 led walker to work

Enhance A 40175 is a quad D-type flip flop. You need a 4017. And power supply decoupling capacitors.
• 20.3k
1 vote

### Maximum LEDs on a pin of an AVR Microcontroller

You are correct in that the microcontroller's pin I/O current spec limits how many LEDs you can drive. In general, you should not exceed the datasheet limits given for I(oh) and I(ol) for a single pin,...
• 55k
1 vote
Accepted

### LED blinking in parallel circuit

It's the same circuit, however you are likely exceeding the rating of the blinking LED. Here is a typical blinking LED and the device is only rated for 14V absolute maximum. So you could permanently ...
• 407k
Accepted

### Why don't LED datasheets specify a maximum rated voltage?

Thinking of LEDs as a resistance is not correct. They are diodes, not resistors, so they have an I-V curve like a diode: Taken from: http://lednique.com/current-voltage-relationships/iv-curves/ So ...
• 17.6k

### Can I safely use the GPIO or opto-IO pin from Basler industrial camera to drive a 64 mW LED?

Your understanding of the opto output sounds correct. You have the example schematics how to drive a LED. The GPIO seems to be sink-only for driving loads, the sourcing current is just for a weak pull-...
• 159k
Accepted

### Can I safely use the GPIO or opto-IO pin from Basler industrial camera to drive a 64 mW LED?

If the GPIO pin can source 50 mA, then a 20 mA load (64 mW, by the way) should not present any problems. LEDs also do not have the potential for creating damaging transients that a relay or other ...
• 20.3k

### turn on an LED with a pressure switch but it will not turn off until you reset the switch

simulate this circuit – Schematic created using CircuitLab This is a canonical circuit for an intro to silicon controlled rectifiers (SCRs). They are generally three terminal PNPN devices with ...
• 20.3k

### turn on an LED with a pressure switch but it will not turn off until you reset the switch

Sounds like what you want is an SR Latch (that's your Google search term). The specifics of implementation will of course depend greatly on what switches you are planning to use - no exact part ...
• 161

### Why is the light emitted by the LED not of a single wavelength but consists of a narrow range of wavelength instead? Spectral linewidth change?

Thinking in just high school physics terms: The energy gap is not going be to uniform since the the literal physical gap between the semi-conductors is not going to be uniform. When they layer the ...
1 vote

### Designing a simple toy dashboard

In addition to what vir said in their answer, and specifically regarding your self-flashing LEDs: There will be a 'tolerance' on how accurately the flash duration is, this can be seen on YouTube when ...
• 161

### Designing a simple toy dashboard

Your post has several questions in it; here are some answers: You do not need a capacitor for this. Individual resistors for the LEDs are required, but some blinking LEDs may not require resistors at ...
• 20.3k
Accepted

### Why do I have to increase the current by 2V when I am using a transistor?

It is dim because the collector-emitter saturation voltage for your transistor is ~2V. Use a logic level MOSFET and a current limiting resistor. You won't be able to get full brightness with a 3V ...
• 20.3k
1 vote
Accepted

### Toggle switch from button and capacitor

A very easy way to do it is to use two inverters, say 74HC2G14, in a feedback loop. This forms a latch that remains in a stable state. When SW1 is in the default position, C1 stores the opposite state ...

### Toggle switch from button and capacitor

Your proposed circuit is sadly never going to work in the way you would like. I show here an LTSpice simulation of a circuit that will allow a simple TACT pushbutton switch to toggle an LED on and ...
• 57.5k
Accepted

### Communication does not occur when connecting an LED to the UART line

As Dave already suggested, change R7 and R8 to 10kOhms. You also need to change R5 and R6 to 150 Ohms because there is too low current available for the LEDs.
• 7,653

Like Elliot said, the fixtures assemblies need to be listed, UL, ETL/Intertek, and others. But I've seen products with ETL or Intertek which were obviously non code compliant. Whether the logos were ...
1 vote

### Calculating current through a diode in a voltage divider circuit

With resistors, the relationship between voltage across and current through them is well known, Ohms law, $V=I \times R$. With diodes (which includes LEDs, of course), this relationship is far more ...
• 39k

### Calculating current through a diode in a voltage divider circuit

Made with microcap v12, mode "interactive". You should add a resistor serial with the other two. You can then "adjust" the start of illumination of the LEDs. Here is an example of ...
• 14.5k
Accepted

### Calculating current through a diode in a voltage divider circuit

Your approach is wrong. The way you have it makes it hard to balance the current of each LED - you can't change the current of one LED without affecting the other. Try this: simulate this circuit &...
• 4,963

### LED without resistor?

While itâ€™s technically possible to connect the LED directly to the STM32 output pin without a current-limiting resistor, I recommend using a resistor for safety and reliability. LEDs are current-...
• 41
1 vote

### Using 5-in-1 dimmable power supply with PWM dimmer for LED strip

The datasheet shows a line-connected PWM module to the control input of the power supply; the one you have is not compatible. A bare potentiometer is probably easier and definitely cheaper than buying ...
• 20.3k
1 vote
Accepted

### Using 5-in-1 dimmable power supply with PWM dimmer for LED strip

The first product is an AC powered dimmer (essentially a dimmer combined with a power supply), the second is a DC powered dimmer (same as the first but minus the power supply). Normally you would use ...
• 17.6k
Accepted

### A simple visual indicator (LED light?) when a USB fan is on

You can add a resistor and LED in parallel with the fan. simulate this circuit – Schematic created using CircuitLab
• 8,061

### Spectrum of LEDs

Just going to dump some datasheet extracts here as I find the patience for fun. E.g. at https://uk.rs-online.com/web/c/displays-optoelectronics/leds-light-emitting-diodes/leds/ we can filter by brand, ...