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Pmodhb3 Necessary For Servo?


Hello again


I was looking at doing a servo project and bought a GWS-S03N servo motor and the HB3 PMOD.  Looking at various sites, I have not seen anyone using the HB3 to control a servo. 


Is the only purpose of the HB3 to allow higher voltages to the servo motor than the Basys2 can output?  It appears that pulse control is still coming directly from the FPGA board.  So, if I used a higher voltage to the PMOD and motor, is there any chance of damaging the FPGA by connecting it directly to the control line of the servo?


Is the HB3 more (or only) intended for driving standard DC motors and not servo motors?



Edited by Josh
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Yes. Most servos are specified at a V+ of 4.8V, and need a TTL level signal for the control pulse. Logic high for a TTL signal is around 2V. This means that any I/O pin that can drive a LVTTL signal will work, but be careful - if you short the V+ voltage to the signal pin you might fry your FPGA. This makes it worth-while to put a 100 Ohm resistor in series to lower any fault current that can occur to a few milliamps.


Digilent have a PMOD that is designed for using with RC servos - PMOD-CON3. If you look at the schematic in the reference manual (http://www.digilentinc.com/Data/Products/PMOD-CON3/Pmod%20Con3_rm.pdf) you will see how simple the connection is.

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