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.
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52 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 ...
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4answers
135 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 ...
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1answer
120 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 ...
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1answer
122 views
Connecting phototransistors or photodiodes in series
I am designing a velocity measuring device and want to use 2 strings of 30 phototransistors in series. The strings are 15mm apart and are illuminated by separate collimated light sources. The output ...
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3answers
179 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 ...
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4answers
179 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 ...
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1answer
58 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 ...
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1answer
246 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 ...
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1answer
192 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 ...
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2answers
823 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.
...
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1answer
102 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 ...
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2answers
182 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.
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1answer
175 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 ...
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1answer
189 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 ...
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2answers
555 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 ...
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2answers
4k 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 ...
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5answers
1k 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 ...
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1answer
1k 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 ...
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2answers
230 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+) ...
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3answers
304 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 ...
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3answers
385 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 ...
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3answers
2k 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. ...
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2answers
272 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 ...
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2answers
233 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 ...
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2answers
355 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.
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4answers
500 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, ...
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2answers
1k 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 ...
