View Full Version : RE: control of a servo with output-pin (3.3volt)
02-04-2007, 09:35 PM
first excuse my verry bad english.
I build a quadrabod with 3DOF.
the servo is a highTurque-Servo with Ncm 274 (Newton-cenitmeters) and a input voltage of
now, l am looking for simple device (transistors ???и or Operation-amplifier)
and schematics to control the servo with a PropStick_USB-pin (3.3volt)
outputPin --------> [device]----------> [signal_In Servo]
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Thank you for your help.
02-04-2007, 10:11 PM
Your English is not less good as mine. Mine is very poor.
Is your servo need 6.0 volt for the power and for the signal line ? OR how y think the servo need 6.0V for power and 5.0v for the signal line ?
In the second case, it's very simple to use a MOSFET transistor.
The BS250 can draw 600mA and work practicaly as a switch.
try this :
outputPIn -----> to the Gate of the BS250 (or similar)
+5V or + 6V -----> to the Source of the BS250
and the Drain to the signal line of the servo
Gate | |
outputPin ----------------|---->| mosfet BS250 or similar one
--------------> servo's signal line
| | <-- this resistor is probably not necessary
and maybe a 1K resistor between the Drain and the ground (normaly not necessary)
This must work with just one transistor and no more. The signal at the servo's signal line is high when the outpunPin is low (It's an inverter).
in medio virtus
Post Edited (inservi) : 2/4/2007 3:31:31 PM GMT
02-04-2007, 10:43 PM
Most servos can be controlled directly from a Propeller. Even though the servo motor and electronics are powered by 6V, the control line is a logic signal, usually considered low when below approximately 0.7V and high above that voltage. You need a protection resistor in series with the Propeller I/O pin, anywhere from 470 ohm to 4.7K usually although theoretically you shouldn't need it (this limits the input current if the I/O pin is accidently connected to a voltage higher than 3.3V or to some other output pin).
02-05-2007, 04:56 PM
hi inservi & mike,
thank you for your quick answer.
now i want buy the stuff and then .... testing.
when i have troubles or antother questions.
i come back
02-05-2007, 09:51 PM
In the case of the servos, the 4.7k resistor is meant to protect the Propeller from back EMF from the servo motor. Again, this probably isn't absolutely needed, but is a nice precaution. For some servos, you may have to lower the resistor value, or go with the transistor amplifier like the one described above. See the this thread: http://forums.parallax.com/showthread.php?p=627842 for another discussion on this topic.
Click here to see my Nomad Build Log (http://share.crustcrawler.com/JohnR/)
02-06-2007, 07:25 PM
thanks for your answer