Phototransistors are in effect a bipolar transistor with a transparent enclosure so light can reach the junction of the base and collector. Compared to a photodiode they offer increased gain, but that comes at the cost of a slower response time.

learn more… | top users | synonyms

0
votes
2answers
33 views

a question about Phototransistor OPB608A

I use a phototransistor OPB608A in my system,shows as below.After capacitor C5, the voltage is 5.5V, that means it will give 5v supply to Pin 1 and Pin 3 of OPB608A, the resistors values are 7.5K and ...
2
votes
3answers
121 views

Light activated switch - avoid flicker when turning on

I have a small light bulb (3W LED, E27/110V) that I am controlling using based on ambient brightness (it comes on when it is dark, and goes off when it is light). The circuit uses a BT136 triac, a ...
4
votes
2answers
157 views

Are photoresistors reliable for light sensing applications?

I've used photoresistors for hobby projects before, such as this one: http://www.foxytronics.com/learn/electronics/kit-guides/starter-electronics-kit-guide/making-an-led-light-sensor However, now ...
1
vote
1answer
68 views

How does a Watt (1mW from a laser) relate to Amps (20mA max current rating for collector of a phototransistor)?

How does a Watt (1mW from a lasermodule) relate to Amps (20mA max current rating for collector of a phototransistor) ? I want to know if the 1mW output from the laser is within or outside the range ...
0
votes
2answers
90 views

How to light a LED using photo transistors output?

I built a circuit using RPR220 photo sensor to detect the surface displacement caused on a material when external force is applied. I could see the output on a CRO even when there are minute changes ...
0
votes
1answer
68 views

Phototransistor responsivity does not match datasheet?

I am making a basic circuit to test the responsivity of a phototransistor. I made a basic circuit using a phototransistor connected to 5V and a 22kOhm resistor. On the other side of the ...
0
votes
1answer
46 views

Detecting and identifying different light sources in arduino?

I want to detect different light sources in arduino. The first Idea about solving this problem came into my mind was to add three light detection sensors (LDR, IR receiver Diode and Photo transistor) ...
0
votes
3answers
157 views

Colour Sensor from discrete components?

I am participating in a robotics competition that requires colour detection using discrete components. The aim is to detect red and green lights of traffic signals. I have tried making a sensor ...
0
votes
1answer
149 views

Control a 3.6V motor (forward/idle/reverse) using two phototransistors facing a smartphone screen

My purpose is to build a cheap quick-and-dirty "robot" using 2 electrical screwdrivers connected to the wheels and a smartphone to control them. I want to control each motor (forward/idle/reverse) ...
1
vote
1answer
129 views

Low-cost phototransistor to MCU interface

The simple way to connect a phototransistor to an MCU is shown in this question. But it requires a Schmitt trigger input which I won't have on my target platform, i.e. either an STM8 at 5V or an ...
0
votes
0answers
142 views

Detecting reflected laser beam

I'm trying to do some distance measurement using laser. But most of the articles I read about are concerned with distance of a few meters and went with simple photodiodes I'm trying to achieve a ...
-1
votes
1answer
80 views

got a too low VCE on a Infrared Phototransistor

I used an Infrared Light Emitting Diode QED123(VF=1.7V) and an Infrared Phototransistor QSD123 in pair. I learnt from QSD123's datasheet that its VCE(SAT) under IC=0.5mA is 0.4V max. But the VCE I ...
1
vote
1answer
71 views

How much gain for optical open-air receiver?

I am planning to make an experimental communications system. I will use a high power LED (≈3watts) Amplitude Modulated with a sound signal and eventually Pulse modulated with digital data for the ...
-4
votes
1answer
225 views

How do I build a light-activated motor? [closed]

I'm trying to build a motor that is activated when light shines on a photoresistor/transistor (can anyone explain the difference?), but I'm totally lost right now. I can only utilize wires, batteries, ...
1
vote
1answer
91 views

Identifying and correctly using this component

I have the two components, which are in the picture below. I have a couple of questions. The first one is, how do I make sure that the IR LED detector is working? I tried searching for specs, but the ...
1
vote
1answer
176 views

Explaining transistor schematic

I have been away of Electronics Engineering since 2008, it seems I missed a lot of basic concepts. I came across this schematic: I found a weird wiring, the capacitor that is tied to VCC, should be ...
1
vote
1answer
330 views

Assistance on values and components, photo-transistor switch for LED array

Yet another photo-switch question. Have done my homework, and searches but most non-specific circuits are beyond my learning curve, time to learn, and available wet-ram. Have a 15 LED array being ...
0
votes
1answer
101 views

Detecting Multiple Lasers

I'm looking to design a game where players fire a gun at a target using LASERS or IR. The target only registers a hit when a certain amount of players (say 3) are hitting the target consistantly for ...
16
votes
7answers
1k views

What was used to detect light before the invention of photodiodes/phototransistors?

Were there technologies before photodiodes/phototransistors or similar semiconductors, which could be used to start or stop machinery based on the amount (or presence/absence) of light falling on ...
1
vote
2answers
336 views

RPR-220 photosensor to logic level?

I have RPR-220 reflective photosensor, which transistor's part I connect to 2v via 10 Kohm resistor. Emitter is then connected to the base of a transistor C547B, which for the test setup uses LED + ...
4
votes
1answer
183 views

Homebrewed phototransistors - unijunction versions

Back in the days, when phototransistors were hard to get (especially in some parts of the world like the communist eastern block), one could brew their own by just filing/sawing off the top of a TO 18 ...
0
votes
2answers
203 views

A phototransistor with LED and resistance in emitter

Earlier I used a simple phototransistor arrangement to detect an on/off signal via a laser pulse. I connected the collector to Vcc(5V), and emitter was grounded through a resistance. The base was ...
4
votes
4answers
360 views

Large Active Area phototransistors? And can solar cells be a replacement

Me and my friends are trying to build a laserharp driven by arduino as a learning exercise. Currently we are using a phototransistor to interrupt the laser light and play music. However the ...
3
votes
2answers
379 views

Reading Array of Phototransistors With Raspberry Pi

For a project I'm working on, I need to read the values from a matrix of phototransistors (8x16) into the Raspberry Pi. I'm not exactly sure how to go about doing this, since I know I need to include ...
8
votes
2answers
609 views

Connecting phototransistors or photodiodes in series

I am designing a velocity measuring device and want to use 2 strings of 30 photo-transistors in series. The strings are 15mm apart and are illuminated by separate collimated light sources. The ...
0
votes
3answers
328 views

Revolutions (pulse) per minute counter circuit?

Does anyone know how to set up a circuit by using counters, decoders, 7 segment displays and a 555 timer to show the revolutions (pulses) per minute from a photo-transistor? I'm doing this as part of ...
12
votes
4answers
216 views

Is \$I_e = I_c\$ for phototransistors?

Due to the base current, in a common emitter circuit the emitter current is a bit higher than the collector current: \$ I_e = \dfrac{1+\beta}{\beta} I_c \$ I was wondering how this is for a ...
0
votes
1answer
121 views

How to calibrate multiple light sensors at once?

I want to build a simple circuit that by adjusting a Trimpot I can regulate the sensitivity of 4 light sensors such as the QRD1114. I prefer to regulate the gain of the phototransistor instead of ...
2
votes
1answer
520 views

Programming methods for detecting liquid drops with phototransistor

I have a simple circuit with an LED pointing at a phototransistor. There is a tube in between them that drops of liquid will drip through at random times. I am reading the voltage with an Arduino at ...
2
votes
1answer
418 views

Phototransistor as a pull-down in digital circuit

I have very little experience with phototransistors. I'm trying to create a circuit that will effectively function as collision detection. I'm using OPB608A which utilizes an NPN transistor. My goal ...
0
votes
2answers
2k views

IR LED - phototransistor problem

Pardon my noobness. I'm trying to set up a simple IR LED - Phototransistor pair but am having difficulties. My setup is just as in the following link, except my resistor values are 1K. ...
0
votes
1answer
176 views

Low Voltage Photosensor

I'm looking for a photosensor/photo IC part (combination of photodiode, linear amplifier, Schmitt trigger and output transistor) that can be powered with 3.3V. Fairchild QSE256/257/258/259 is almost ...
6
votes
2answers
293 views

200+ phototransistors and reading them

Im hoping to get some suggestions and ideas on how to read in 200+ phototransistors voltages (0-5) into an ADC? I only need to look at 1 by 1 rather than all at once.
6
votes
1answer
261 views

Designing a wide-range light detector circuit

I'm looking for a few hints in designing a light detector circuit. Priorities are that the circuit is simple (both as in few parts and as in relatively easy to understand), rather cheap, and can ...
1
vote
1answer
303 views

How do i build a laser based tachometer?

I want to build a tachometer that has to be somewhere around 1 meter from the rotating shaft. I'm still to build a prototybe based on IR diode and phototransistor, but I'm afraid, I would get too ...
6
votes
2answers
920 views

Phototransistor Dark Detector Circuit

So I've decided to make a circuit based on this: I have a few questions. First of all, when the photo-transistor switches off and Q1 switches off, as per the article, what is the voltage going ...
4
votes
2answers
13k views

Light sensor using Photo Transistor

How can I design a circuit which utilizes a photo-transistor to make a light sensitive switch that is when there is no light in room, the led connected to the photo-transistor lights up and when there ...
11
votes
5answers
2k views

Sensor for detecting airsoft bullet

I'm trying to make airsoft chronograph/chronometer (a device that measures airsoft bullet speed). The idea is to measure time in which bullet is traveling from point A to point B, and then I can ...
1
vote
1answer
2k views

Simple IR pulse detector with IR phototransistor

I understand the basic circuits used with phototransistors: I believe that this is essentially a voltage divider, commonly used for all sorts of analog sensors. In the left circuit, in the dark, the ...
2
votes
2answers
468 views

LDR Component Obsolescence

The Light Dependent Resistor (LDR) that I use in MintyTime, Excelitas Tech VT93N2, has been discontinued by the manufacturer. I'm having trouble finding a comparably priced (e.g. < $0.50 @ 100+) ...
3
votes
3answers
385 views

Remote Control Design

I am want to design a remote control. All I need is the appropriate IR LED and the Receiver to use, that will yield optimal performance. i need real practical experience here. What is the best ...
0
votes
3answers
563 views

Cheapest way to measure .1uL volume of liquid being dispensed from pipette tip

So I think this is going to be some kind of sensor... :P I'm looking for ideas on the best way to measure a dispensed volume of .1uL from the tip of a pipette This is for a open source medical ...
5
votes
3answers
4k views

Phototransistor transimpedance amplifier

I have a typical NPN phototransistor. I have it working in a common-collector configuration; see figure 2 of this app note. Increasing Re will increase the sensitivity, but decrease the speed. ...
5
votes
2answers
481 views

combining phototransistors

How to connect phototransistors in an additive style? The output current should resemble the total power of light received by all of them. Eg. if one gets 0 lux, the other one 10 lux, the result ...
3
votes
2answers
315 views

Light detector linearity with varying wavelength

Given the same intensity of light, in varying wavelengths, which is typically more linear with their output: Cds (photo resistor) or a Photo transistor? I would assume that the junctions in the ...
2
votes
2answers
517 views

Where is photodiode in the CD/DVD drives?

Where is photodiode in the CD/DVD drives? What is his frequency response & sensetivity usuallY? I am going to try laser data transfer, but finding decent photodiode is my weak point.
5
votes
4answers
562 views

How can I generate a logic pulse from a broken IR beam?

I would like to trigger a [7]555 timer when a phototransistor stops receiving light from an IR led, more precisely when the (expected to be smallish) signal from the light-sensitive voltage divider, ...
4
votes
2answers
2k views

IR LED Detector question

I need to buy some IR LED Detectors but I am having a hard time finding anything except for the 940nm. It seems that there are only three types of IR LED emitters and detectors sold. 850nm, 880nm ...