| Re: Störung auf linker radencoder: entwurfsfehler Kategorie: Pro-Bot128 (von PepeV - 30.03.2010 10:12) | |
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Als Antwort auf Re: Störung auf linker radencoder: entwurfsfehler von Mansfeld - 23.03.2010 16:34
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> > The outputs of Timer T1 PWM X (X1_3 / OC1A and X1_2 / OC1B) couse interference on the collector > > of the left wheel encoder phototransistor T3, which is connected to input port X1_9 / INT7. This is > > coused by a design error on the printed circuit board of the drive unit. > > > > On the top side of that board the wire that runs from T3 to CON2 runs very close and parallel to the two > > lines on the bottom side that carry the PWM signals for the motors. The result is that INT7 (left counter) > > receives extra pulses from interference and the robot will not drive strait at low speeds. (At low speeds > > the pulses from the phototransistors are less steep and therefore more sensitive to interference.) > > > > I solved the problem by disconnecting the printed wire from T3 to CON2 (cutting it near T3 and CON2) > > and replacing it with a shielded wire. But hopefully the designers will find a more elegant solution by > > altering the printed circuit board. > > Hi Pepe, > thats a very interesting report. U. Sommer recommends in his book to > insert two Schmitt-Triggers between collector of T3 / T4 and the > Prozessor pins X1_9 and X1_10. > How did you GND the shield: On both ends, sender end or receiver end? > (I don't own a scope, I can't watch the result). > Regards > Fred > Hi Fred, I grounded only one end of the shield to prevent 'ground loops'. I chose the receiver end but I don't think it matters very much. Maybe you want to read my contribution 'Improving the wheel encoders' too. Together with the above this really is a big improvement and you will not need the Schmitt-Triggers anymore. Regards, Pepe | |
Antwort schreiben Antworten:  Re: Störung auf linker radencoder: entwurfsfehler (von Mansfeld - 31.03.2010 15:51) | |
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