About like this: http://johannes.eventify.de/kiste-temp/Voltage_shifter.jpg That's the same thing I described except the 100K in series with the motor (which is the V+ source in this case).
Which is the output impedance on "to analog input" line? I think 100K... Not quite, although you're right, the 100k is a bit high. The OP-Amp controlled transistor however exhibits a far lower impedance. But you're right, make the resistor at the motor 22k, and the one below the transistor 2.2k. That's still enough protection for the transistor if the on/off pin is accidentally driven high ;-) > Replace the BC547 with a 500mA darlinghton, 0-2.5V with a variable reference > voltage from PIC, and 10K resistor from the emiter with a smaller resistor, > 100K with 0 ohm. I'm sure you will be surprised how little you can lower that voltage even with quite a large current. But yes, the 0-2.5V shall be the reference voltage from the PIC. > Forget about the Hz to GND line since you're able to switch off the > reference, but add 10K from Vref to ground to avoid false current generation > if Vref becomes by accident an input. Agreed, with a pull-down the voltage is likely to be "GND" enough to omit the on/off line. > When the motor is generator, any load will decrease the EMF voltage in the >same way any mechanical load on a motor is increasing the current sourced Good point! If the motor runs at no-load speed and you short the pins, it generates the same current as the one given for "stall". For that little 0.85 Watt/3 Volt motor I linked, it would be 2.63 Ampere. And it would be braking with 7.32 mNm. Again, you would be surprised how hard it is to pull down the voltage. And you mentioned a very interesting point I will probably one day investigate further on: Why not filtering the voltage? But I would start the other way round: I would take out the ripples from the PWM by a LC low pass filter, and use a high-pass to the "sense" input, perhaps from a shunt to get the current instead of the voltage. I'm sure you can count the rotor coils passing the magnets or the commutator switching over. So you could actually measure distance, not only speed. Greets, Kiste -- You received this message because you are subscribed to the Google Groups "jallib" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/jallib?hl=en.
