After watching Adrien Lelong's EHSM talk about bouncing signals into wires and figuring out the condition of the wire (broken, shorted, spliced, etc.) from the shape of the pattern that comes back, I wonder if there wouldn't be a cheaper way to accomplish such things.
The basic setup is that you send a pulse with a DAC, then receive what comes back with an ADC, and then do some processing, either offline, or in real time with an FPGA, DSP, etc. One issue is that fast ADCs are pricy. Fast DACs are cheap. If all else fails, you can make one with a bunch of resistors. Now, I wonder if one couldn't accomplish similar things with a much simpler setup: instead of a fast ADC, you'd use a slow ADC. For signals within the ADC bandwidth, it would act as usual, which may be useful for some broad characterization. For signals much faster than the ADC bandwidth, the ADC could act on the integral of the signal, combined with a window function. The window function could just be a gate, operating at a speed similar to that of the DAC. For example, to determine when exactly a pulse begins coming back (it may come back as several pulses), one could open the gate from time 0 to an initial estimate t, and then, for a second measurement, from t to "infinity". In the simplest case (we just check if there's a signal or not) there would be four possible outcomes: Signal received in interval Interpretation 0 to t t to infinity ----------------------------- -------------------------------------- nothing nothing there is no reflection something nothing t is after the last major response nothing something t is before the first major response something something t is in the middle of the response(s) You'd then adjust t, e.g., with a binary search, until you find the point at which the first interval changes between "nothing" and "something". Interpreting the amount of energy seen by the ADC (i.e., the charge built up during integration), varying the window, varying the shape of the outgoing pulse, etc., would allow for a lot of additional degrees of freedom to further dissect the wire's response (alas, using math that's a bit beyond me). I wonder how much one could accomplish with such a setup. Even simple MCUs have peripheral speeds in the tens of MHz, so it should be possible to have fairly good time resolution with quite simple means. - Werner _______________________________________________ Qi Hardware Discussion List Mail to list (members only): [email protected] Subscribe or Unsubscribe: http://lists.en.qi-hardware.com/mailman/listinfo/discussion
