Laser Receiver - What is the Time Response?

Hi Everybody!

I'm making a project of a Laser Harp. Basically I will use KY-008 for the "strings" and a receiver in a glove. My question: does anyone knows what is the time response for this receiver?

I'm using a LDR right now, and I have a lots of problem with the time response. I need to put a lot of delay in the code in order to maker the thing work. LDR demands 30 ms to send the signal to the arduino, and I would like some response in us or ns if possible.

Thanks!!

That ebay link, who knows what it is.
Probably a photo transistor.
Photo transistors are a lot faster than an LDR.

Sensor in a glove?
The laser has to shine exactly on the sensor, and the sensitive area of a photo transistor is a lot smaller than an LDR.
Could work as a beam break sensor though.
Leo..

Wawa:
That ebay link, who knows what it is.
Probably a photo transistor.
Photo transistors are a lot faster than an LDR.

Sensor in a glove?
The laser has to shine exactly on the sensor, and the sensitive area of a photo transistor is a lot smaller than an LDR.
Could work as a beam break sensor though.
Leo..

The sensitivity area of the LDR is, in fact, a lot better than the photo transistor. In my project I don't have any structure above the lasers so I can't use as a "beam break sensor". That's why I want to put the receiver in a glove.

The common laser harps have a sensor in the floor, and the reflected laser triggers the sensor. I don't want to do like this because I want to minimize the interference of ambient lights.

Do you know any photo transistor with high sensitivity for visible light and high speed response?

The KY-008 seems to emit 650nm red light.
Google "650nm photodiode" or "650nm phototransistor" for lots of laser detector hits.
Leo..

The sensitivity area of the LDR is, in fact, a lot better than the photo transistor.

But, as you have noticed, is extremely slow.

Photodiodes can respond in picoseconds if used properly, and some have areas larger than a typical LDR. The larger the photodiode area, the slower to respond. This one, with 1 cm x 1 cm area, has a rise time of 7 us.

Ambient light might be a problem with a glove.

With a beam break system, you can have several 'strings'.
How are you going to solve that with a glove.
Leo..

First of all, sorry for the English If anything is incorrect.

Thank you jremington! You Said "picoseconds If used properly". That means there is some way to speed the Rise time of this component, for example? Reducing 7us to Something faster? How?

The sensibility of the component is "fixed" or adjustable as well? How? I'm asking If It can be regulated for the amount of Lux received in order to switch.

Wawa,

The Beam break system was the First Idea when I decided to do the project. It is a simple way to do It, and it's called "Framed Laser Harp". That requeries a large structure above the lasers, since I'm going to play standing. This method prejudice the transportation of the instrument to other places... My project is the "Frameless" type.

I don't know If It Will works, but the glove's function is exactly to reduce the ambient light problem. Imagine that you have your hands turned to the floor, with the sensor "looking down". That way the sensor doesn't receive direct light...

The harp Will have 8 string, 8 lasers, and a pedal to change octaves. The system turns ON and OFF each laser in a sequence. The code tests If the sensor received light and look for the laser that is ON in that moment, in order to know which note It has to play (that's why I need fast response). It is already working with 2 strings, but with more, the delay in code turns to be a problem.

That means there is some way to speed the Rise time of this component, for example? Reducing 7us to Something faster?

Yes, reverse bias it. Also note that the quoted 7 us is with a 1K resistor load, so it would be 0.7 us with a 100 Ohm load. You probably don't need a 1 cm x 1 cm area, either.

But even 7 us rise time should be more than fast enough for your application, especially if you are using a 16 MHz Arduino.

jremington:
Yes, reverse bias it. Also note that the quoted 7 us is with a 1K resistor load, so it would be 0.7 us with a 100 Ohm load. You probably don't need a 1 cm x 1 cm area, either.

But even 7 us rise time should be more than fast enough for your application, especially if you are using a 16 MHz Arduino.

Perhaps you all are looking at the wrong end of the problem. If the code is using an interrupt, that interrupt is triggered the instant the pulse rises above a minimum threshold, not when it reaches a 5 volt peak. So, any rise-time above that threshold is not used.

Does the same apply to "reading" a regular digital input?

Paul