Skip to main content
41 votes

Why aren't garage door sensors retroflective on one end?

A reflector might accidentally be substituted by some reflective aspect of an obstacle, say a chrome plated fender on a bicycle, motorcycle, classic car... or even the reflector on one. In contrast a ...
Chris Stratton's user avatar
28 votes
Accepted

Any better way to determine source of light by analyzing the electromagnectic spectrum of the light

You really are looking for someone who's already solved this, I suppose. But I don't know of any project, myself. So all I can offer are some thoughts to consider. On spectrometers: For a ...
jonk's user avatar
  • 78.3k
23 votes

Thin wall to block LED light from hitting photodiode?

My advice is to not bother doing what you're doing, and spend the $3.50US to get the part designed for the task, like https://www.digikey.com/product-detail/en/osram-opto-semiconductors-inc/SFH-7060/...
Scott Seidman's user avatar
23 votes

Will a 950 nm IR emitter work with a 870 nm phototransistor?

Side by side: - The receiver will be slightly off centre compared with the transmitter (purple lines I added are sitting at 950 nm) but the receiver will still be above 80% of its optimum sensitivity....
Andy aka's user avatar
  • 462k
22 votes

Why aren't garage door sensors retroflective on one end?

A white card placed in the beam close to the transceiver end will fool the beam. A transmitter-receiver pair across the space to be protected is much more resistant to defeat in this fashion.
elchambro's user avatar
  • 951
20 votes
Accepted

Night light, schematic and functioning

simulate this circuit – Schematic created using CircuitLab Figure 1. Redraw of the OP's reverse engineering. If your circuit is correct then we can see three voltage dropping resistors, R3, 4 ...
Transistor's user avatar
  • 177k
19 votes

Will a 950 nm IR emitter work with a 870 nm phototransistor?

Yes, your system will work. Consider the system spectrum (red line below), which is each sensitivity at each wavelength times the emission at that wavelength. You can see that the transmitter is ...
jonathanjo's user avatar
  • 14.4k
14 votes

Why aren't garage door sensors retroflective on one end?

The typical LiftMaster/Chamberlain safety sensor system is designed to prevent it being accidentally or even easily deliberately disabled. Interposing a reflector, an electrical short or an electrical ...
Spehro Pefhany's user avatar
10 votes

Will a 950 nm IR emitter work with a 870 nm phototransistor?

Yes, it will work. Look at the sensitivity/emission vs wavelength curves. It is a spread and there is a point of overlap where both devices have reasonably high values.
DKNguyen's user avatar
  • 56.8k
8 votes

How to tell how sensitive a photodiode is?

Depending on the speed you need, you may well be out of luck. You state that your current diodes "with a picosecond level rise and fall time", while you link to a PD with 12 nsec rise and fall times. ...
WhatRoughBeast's user avatar
7 votes

Photodiode robust enough for laser?

The photons from a red laser aren't any more energetic than those from a flashlight. Red light corresponds to a photon energy of 2 eV, which isn't much in the grand scheme of things. Ultimately, the ...
uint128_t's user avatar
  • 8,734
6 votes

Night light, schematic and functioning

The LEDs and D4 create a simple half wave rectifier. The resistors R3, R4 and R5 provide the necessary current limiting. C1 provides very simple decoupling. When the LDR has light on it, it's ...
Brendan Simpson's user avatar
6 votes

Light reading diode?

Why not using a dedicated UVA/UVB sensor for that, like the VEML6075 breakout board or the VEML6075 basic IC?
Michel Keijzers's user avatar
5 votes
Accepted

Confusing dark sensor circuit diagram

This is a crappy circuit. Run away. It seems the intent is that when there is lots of light, LDR1 goes down in resistance, which turns on Q1, which turns off Q2. When it's dark, Q1 doesn't turn on ...
Olin Lathrop's user avatar
5 votes
Accepted

How to tell how sensitive a photodiode is?

How to tell how sensitive a photodiode is? There's a curve in your device's datasheet that tells you exactly that: Combined with the line in the Characteristics table that tells you the sensitivity ...
The Photon's user avatar
  • 131k
5 votes

Photodiode Circuit Output Saturating to 0V. Is there a way to salvage these boards?

Suffice it to say all channels are identical? So, concentrating on one: We have an inverting configuration, which takes the photocurrent (drawn from the +5V bias source) into a virtual ground / ...
Tim Williams's user avatar
  • 37.8k
4 votes
Accepted

Using multiple white LEDs to obtain a unique CCT

The problem with CCT has been you have to buy binned LEDs to get the correct mix. But if you use two drivers, white and Red LEDs, then binning is not required. Use high power cool white and mix with ...
Misunderstood's user avatar
4 votes

Switch triggered by flashing light

Olin's suggestion of micro-controlled system will definitely provide you with the most control and flexibility but if you want to mess around with a linear solution the following circuit sort of works ...
Trevor_G's user avatar
  • 46.8k
4 votes

Reflective optical sensor

"Daylight" is full of various wavelengths of light, including infrared. In daylight, your sensor will "see" infrared from the mishmash that is sunlight, and react the same as if it ...
JRE's user avatar
  • 72k
4 votes
Accepted

Meaning of two ADC channels in an LTR-559ALS-01 optical sensor

The two channels are connected to two different light sensing diodes: One is sensitive to IR only The other is sensitive to IR + visible light This gives you more flexibility in choosing what ...
jusaca's user avatar
  • 9,609
4 votes
Accepted

Can we program our smartphone camera to detect the frequency and time period of IR light?

It depends on whether the smartphone camera actually sees IR. Most seem to these days. More here: https://petapixel.com/2019/08/22/how-i-shoot-infrared-photography-with-a-smartphone/ This article ...
hacktastical's user avatar
  • 54.5k
4 votes
Accepted

Measuring ambient light intensity using BPW34 photodiode and TLC271ACP opamp

If the IN- pin is varying from 0 to +400mV the photodiode is probably connected backwards. The circuit seems correct. The input current from the photodiode should be such that the input goes negative. ...
Kevin White's user avatar
  • 33.8k
4 votes

DC transimpedance amplifier feedback capacitor

It actually restricts the bandwidth but improves stability. Its necessary value depends on the actual type of opamp and its input capacitance. Without it, the transimpedance amplifier might oscillate ...
tobalt's user avatar
  • 22.3k
4 votes
Accepted

DC transimpedance amplifier feedback capacitor

Yes, the feedback capacitor is necessary with most op-amps. Op-amps don't like capacitance to ground on their negative input, and photodiodes generally have lots of area, which means lots of ...
TimWescott's user avatar
  • 46.6k
3 votes

Photodiode robust enough for laser?

No it won't burn but you could be heavily saturating any amplifier following the photodiode. In the photodiode data sheet it shows a graph of output current for an input light power density of 10 mW ...
Andy aka's user avatar
  • 462k
3 votes

Is it possible to replace a two way switch with two wall PIR sensors?

Easily done: 3-Wire Sensor 2-Wire Sensor
Jack Creasey's user avatar
  • 21.8k
3 votes
Accepted

What is used to detect light from fiber optic signals in high speed Internet?

Yep, high speed photodiodes are the simplest way to do this. A receiver will usually consist of a photodiode and transimpedance amplifier (current in, voltage out). After that, it's just a high speed ...
alex.forencich's user avatar

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