United States - Flag United States

Please confirm your currency selection:

Bench Talk for Design Engineers

Bench Talk

rss

Bench Talk for Design Engineers | The Official Blog of Mouser Electronics


Seeing The Light: A Circuit For Interfacing With Ambient Light Sensors
On November 12, 2014 in All, MultiSIM BLUE by Mike Parks
Mike Parks

We built a smart mailbox, as related in an article, that had an ambient light sensor to detect when the mailbox door was opened. In that project we used a Vishay ambient light sensor (Mouser Part #782-TEPT4400) that acts very much like an NPN transistor, in fact the part is also referred to as a phototransistor. The difference being (when compared to a normal bipolar junction transistor) that instead of needing a base lead to setup the bias voltage, photons provide energy at the base-collector junction to turn the transistor on, thus allowing current flow from collector-to-emitter.

In that project we were solely worried about the presence or absence of light, not accurately measuring the intensity of the light. Thus we got away with a pretty simple voltage divider circuit to measure the light. In other applications you might be concerned with accurately measuring the light intensity with greater resolution. If your project needs that accuracy, there are many circuits that can give you that resolution. One particular implementation utilizing an operational amplifier (op-amp) is this circuit here:

An advantage to this circuit is that it provides a nice, clean linear voltage output as a function of the amount of light hitting the phototransistor.

One caveat about using phototransistors vice other optical detector components such as photodiodes, while they have better responsitivity (measure of output voltage per unit of optical input), it comes at the expense of longer response times for the output voltage to reflect changes in the amount of light striking the base-collector junction. Therefore, different optical components may be required if you need to deal with extremely fast-changing light sources such as high-speed digital optical communications applications.

 

*** All circuits were done in the new MultiSim BLUE from Mouser and NI. Check it out at www.mouser.com/MultiSimBlue.

« Back


Michael Parks, P.E. is the co-founder of Green Shoe Garage, a custom electronics design studio and embedded security research firm located in Western Maryland. He produces the Gears of Resistance Podcast to help raise public awareness of technical and scientific matters. Michael is also a licensed Professional Engineer in the state of Maryland and holds a Master’s degree in systems engineering from Johns Hopkins University.


Related Posts

  • New Tech Tuesdays: TE Connectivity Lights the Way with LUMAWISE Motion Sensors

    Discover the cutting-edge technology behind TE Connectivity’s LUMAWISE Motion Sensors, revolutionizing street lighting with precision and efficiency. Explore how these sensors redefine urban illumination, setting new standards for reliability and interoperability.

  • LEDs and the Road to a Brighter Future

    Improvements to the industry-leading XLamp® XP-G LED product family can significantly impact and benefit next-gen or new system designs, marking a key breakthrough for many high-power LED applications, notably in light output, light directionality, efficiency, and reliability.

  • Feeling Blue? Human Health in Light of LED Streetlights

    White LEDs used in street lighting may consist of packaged combinations of Red, Green, and Blue LEDs, but more often than not employ blue LEDs, which are built generally from indium gallium nitride (InGaN) and have a yttrium-aluminum-garnet (YAG) (Y3Al5O12) phosphor coating placed on their emitter or emitter’s optic. From the base color of blue light, white light can be realized and utilized for white LED streetlights. But does this blue light found in LED streetlights make humans experience any negative impacts?

  • Keeping the Lights On: ESD and Thermal Protection for LED Lighting Systems

    There are several factors that can affect solid-state lighting including stress, packaging-related, and component-related issues. Discover the key threats that affect the reliability of LED lighting systems.

  • New Tech Tuesdays: The Dawn of a New Thermal IR Detection Era

    As the world of thermal infrared sensing evolves, advancements in TMOS sensor technology represent a significant leap forward for infrared thermal detection. However, PIR sensors, with their proven reliability and specific applicability, continue to have a significant place in certain applications.

  • Circuit Protection without Circuit Protection Components

    Have you ever thought about circuit protection as analogous to fire protection? There are lots of ways to prevent fires. There are active systems (fire sprinklers, automated extinguisher systems) and passive systems (self-extinguishing materials, self-closing fire doors) and safety-by-design systems where careful selection of non-flammable and insulating materials as well as physical layout make fire propagation nearly impossible. As it turns out, circuit protection has similar options. Here is an example of circuit protection via a safety-by-design technique...
29030 Views
Tagged With: Ambient Light Sensor, MultiSIM Blue, Op-Amp, phototransistor, Vishay

Search

Categories

Featured Authors

All Authors

Show More Show More
View Blogs by Date

Archives