DSO 150 : (Slow) Timebase
Slow Capture So far, we've captured up to 1ms/division just by selecting the right ADC scaler & rate ( and dropping some samples). What about slower capture ? i.e. 5mS/div or 100ms/div ? One option would be to do oversampling i.e. capture much more data at 1ms/div and drop a lot of them That would require large amount of RAM, for nothing. The other option is to use a timer. The scheme is as follows : * Start a timer and ask for N ADC samples * When the timer elapses, average the N samples and start a new ADC sampling sequence * When we have the required number of points, done ! It was a bit tricky to do because there were more timer interrupts than expected (for reason unknown so far). Triggers The trigger is based on a OP-Amp comparator, with its output connected to PA8. The relevant part of the JyeTech schematic is that one : When input (after scaling) is higher than Vref, PA8 is "One" When input (after scaling) is lower than Vref,