It can be used as an interrupt to trigger successive ADC conversions, rather than letting the ADC convert the data at some random speed. "Convert" is a clock that runs at a fixed frequency of 31.772kHz. Please consider writing about your tests and their results so that other people using this open source device can benefit from your experience :). It is the ratio of the return time to the sync time that is a constant. As a result, all measurements need to be taken as a proportion of the sync time. The sync signal is NOT at a constant frequency - it drifts with temperature. Conversely, the return signal can change very fast so a quicker algorithm may be needed. This is because there is plenty of time to collect the zero data and perform complicated statistical or correlation mathematics, since it is not changing. In practice, you often find that the algorithm measuring the zero is much more accurate than the one measuring the return signal. Of course, using different algorithms changes the offset between the zero and the return, but since they are not perfectly matched anyway, you always need to include some offset in software. The reason is that the zero has a very stable amplitude whilst the return signal has a continuously changing one. It is not necessary to use the same algorithm on both the return signal and the zero. This gives the best signal-to-noise ratio (SNR). A good rule of thumb is to adjust the threshold so it is about half the height of the return signal. If you don't want to use an ADC then you can dynamically adjust the reference voltage of a comparator, typically by using a PWM output and setting the duty cycle. Of course, this can be done in software if the entire waveform has been digitized. In many professional LRFs it is a dynamic level that is adjusted according to the strength of the return signal. There are many different strategies that can be used to set the threshold. You are asking about some of the critical issues that face LRF designers and you can probably imagine how much harder these issues would be to resolve if the signals were all running at the speed of light. I'm delighted to see your questions on this forum. This is a pretty complicated modification and will perhaps form the basis of a future discussion! If you really want to break new ground, the OSLRF-01 circuit is capable of quasi-phase measurement, a much higher resolution method of measuring a distance. This will give you a very clear idea of how each change to the design affects the performance. These kinds of modifications should be done whilst watching the expanded timebase signals on an oscilloscope. Reducing the power and pulse width of the laser will help. Just remember that with a smaller lens on the laser, the beam intensity goes up and you could exceed the Class1 eye safety limit. There's nothing that prevents different lens combinations from being used, even to the extent of having no lenses at all! You can use a smaller lens on the laser - perhaps one of those that you get inside visible laser pointers, and you could leave the lens off the detector so that there are no parallax effects.įor short range measurements, you could also try running the laser at lower power (change the voltage regulator) to reduce electrical firing noise and also narrow the width of the laser pulse (RC network) to get a cleaner signal. I can't say for certain that the OSLRF-01 will meet your requirements but it's these kinds of unusual applications that make this open source product such an exciting platform to run experiments on.
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