I need to detect pulses of visible light in a dark room. The light is likely to be relatively low intensity and I need to record the timing of the pulses to an accuracy of less than 10ms.
I'm assuming an LDR will be too slow, so I'm looking at phototransistors ... at which point I start getting out of my (electronic) depth.
What parameters would determine an appropriate phototransistor?
I'm expecting a circuit something like this ...
... but am wondering whether it will be sufficient. Any advice?
In a pro audio environment, due to the different paths synchronus audio and video signals take, there can be significant delays introduced.
The goal is to play 1 frame video flashes and corresponding bursts of sound, and to measure the delay between them so you can compensate at a software level.
There are (relatively expensive) devices commercially available and the application has been discussed in at least one other thread. I'm just trying to skin the cat my own way and I've not seen this aspect of the physical electronics discussed elsewhere.
Just check the datasheet.
Response times are often significant, both have the same subtimes.
we have no knowledge other than what the manufacturer has determined. The choice is yours
Photo transistor is known to be faster in general, but I couldn't see a difference. I don't have fast enough devices to measure the speed of these materials. We cannot understand this with normal measuring instruments. normal processors may fail. faster and larger memory may be required
If you are an expert in software, I am sure you will succeed. 'Cause you're gonna raise the Evereste flag
The way to eliminate factors such as noise is you can add a focus lens or electronic filters you will need to add a window covering the wavelength.
However for your application you dont need GHz responses. The fastest monitors have a response rate of about 1msec.
A phototransistor (or photodiode plus a transistor) will do the job. Here is a circuit I built to detect light pulses
You can use the same arduino to generate pulses for testing - just use the default PWM on pin 5 or 6 which give 1kHz approx, and use
Thanks all. Especially for the last YouTube link.
If the diferences between diodes and transistors is nano seconds, it sounds as though the extra sesnitivity of a phototransistor will be more useful in a low light use.
Phototransistors are orders of magnitude slower (response times typically 1 to 10 microseconds) compared to photodiodes, but a phototransistor should be fine for detecting output changes of a monitor screen.
