I was looking a varioos laser measuring devices (laser tape measures). Most of them seem to be accurate within 1/8th of an inch. I'm wondering what the limiting factor for accuracy is. Is it simply a calibration issue? the quality of the electronics?
Electronic – What would make a laser measuring device more accurate
devicelasermeasurement
Related Solutions
Laser diodes are like LEDs in that the more current you put through them, the hotter they get, and the hotter they get, the more current will go through them, which makes them get hotter... and then fzzt.
So yes, as BarsMonster says, without anything to regulate the current (in the simplest case, a current limiting resistor) the laser diode will die immediately.
You've misread the data sheet. Nominal operating current (according to the data sheet) is ~200 mA. In fact, the 400 mA limit is mentioned nowhere in the data sheet, and I'd guess you got it from the eBay listing. A word of advice - when it comes to believing an eBay listing or a data sheet - go with the data sheet. With this in mind, your best bet (for consistent power levels) is
simulate this circuit – Schematic created using CircuitLab
I recommend that you find a copy of the LM317 data sheet and read it. The circuit is one of the application circuits. The biggest drawback of the circuit is that the LM317 will dissipate nearly 2 watts, so you need a decent heat sink on it.
Going with the 5 volts supply/resistor is workable, but the resistor should be 10 ohms, in order to limit the current appropriately.
And don't forget to heatsink the laser.
Best Answer
-The way how the laser is used is the limiting factor. I list a few ways and their accuracy that I can think of.
Angle of reflection: angle is measured with a line sensor. The location of the peak intensity is proportional to the distance. Accuracy is related to the line sensor pixel size and the algorithm. I have seen accuracy = 100 um sensors with range of 30 to 50 mm, so 0.05% of the distance.
time of flight: Calculate how long does it take for pulse to travel to target and back. Accuracy related to sampling speed and measured distance... 1/8th of an inch requires 5 GHz sampling rate.
interferometry: accuracy is the same order as wavelength of the laser (red 600 nm). This requires some mirrors and steady instrumentation (read: expensive), so not for all applications.
I think that your tape measure uses time of flight (TOF) measurement. There are specialized TOF chips, so you don't necessary need a fast microprocessor.