Simple Servo Controller

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Servo motors have many uses in everything from robotics to puppetry to photography and beyond. These little motors can position their output shaft to any position on command and hold that position. Most servos have a range of motion to about 210 degrees and thankfully are very easy to control with a simple circuit such as the one presented here. Using just a 555 timer and a few support components this circuit can control a servo through it's full rotation based on the position of a pot. This circuit was originally published in the Think Tank column of the October 1995 issue of Popular Electronics.

Schematic

Parts

Part	Total Qty.	Description	Substitutions
R1	1	820 Ohm 1/4W Resistor
R2	1	68K 1/4W Resistor
R3	1	10K 1/4W Resistor
R4	1	1K 1/4W Resistor
R5	1	1K Linear Taper Pot
C1	1	1uF 16V Electrolytic Capacitor
Q1	1	2N3904 NPN Transistor	2N2222, Most Small Signal Transistors
U1	1	555 Timer IC
MISC	1	Board, Wire, Knob For R1, 8 Pin Socket For U1

Notes

R1 adjusts the position of the servo.

Connect the servo to the circuit as shown in the schematic. For common Futaba servos, the red wire is power, the black wire is ground, and the white wire is control.

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Comments

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soorya Simple Servo Controller Wednesday, May 30, 2012 2:57:58 AM

what should we give in the controller?? i mean how should be the input?? could you give a table of inputs and the angle turned???

wasi Simple Servo Controller Thursday, November 03, 2011 3:55:25 AM

yesterday i assemble this ckt .this ckt does not work when i inserted the R2 resistor of 68 kilo ohm wit base of transistor in series

Edwin Smith Simple Servo Controller Tuesday, October 11, 2011 5:09:53 AM

I need some help changing this circuit. I have a single on of switch and want to us it to set the servo to minimum and maximum by simply turning it on or off. Will proley be good to have a variable pot in order to set the minimum/maximum position to fine tune. Please advise. I wanna make a number plate flipper for my bike with a servo. So On must be flipped up and off must be flipped down.

ACA Simple Servo Controller Sunday, July 03, 2011 9:38:42 AM

Question : can the other comparator be used to sense voltage drop in the vcc,and set different values for pin 6,as to make it switch H and V skew depending on receiver polarity?

ACA Simple Servo Controller Sunday, July 03, 2011 9:19:01 AM

I would like to suggest to add an IC where the pot is,and use the 13v/18v as reference to vary the resistance between 2 states for U1,in this way,you can feed the power from the LNB cable,and it will be possible to change skew according to polarity automatically.,with no power supply needed.

Arno Simple Servo Controller Wednesday, March 02, 2011 10:11:06 AM

Normaly, it will work with all kind of servo, maybe not with the digital ones..?!! But, like said in the comment uper, it is just a question of wire's color !

richard Simple Servo Controller:::::question Wednesday, December 29, 2010 7:36:24 PM

is it working in other servo motor or only in Futaba servos?

mrel Simple Servo Controller Saturday, November 06, 2010 8:39:55 PM

Schematic not to clear U1 (555) Is Capacitor C1 postive side connected Pin (1) and to Pin (2) and Pin (6) of U1 (555) chip? mrel

Fadil Simple Servo Controller Saturday, September 25, 2010 11:02:10 PM

Just like craig and john said earlier...I have the same problem too.All I need is to control the motor from 90 to 0 and 0 to 90.But my servo twitches once whenever I switch the circuit on.Please help me

Tony Simple Servo Controller Friday, August 06, 2010 2:14:50 PM

I hooked up the circuit on a proto board--it works pretty well, but I found it sort of noisy. In "Practical Electronics for Inventors," by Paul Scherz, it shows a 1000uF cap across the positive and negative inputs to the motor (page 933 of 2nd Edition). I tried a 5uF one and it cured the noise.

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soorya	Simple Servo Controller	Wednesday, May 30, 2012 2:57:58 AM
what should we give in the controller?? i mean how should be the input?? could you give a table of inputs and the angle turned???
wasi	Simple Servo Controller	Thursday, November 03, 2011 3:55:25 AM
yesterday i assemble this ckt .this ckt does not work when i inserted the R2 resistor of 68 kilo ohm wit base of transistor in series
Edwin Smith	Simple Servo Controller	Tuesday, October 11, 2011 5:09:53 AM
I need some help changing this circuit. I have a single on of switch and want to us it to set the servo to minimum and maximum by simply turning it on or off. Will proley be good to have a variable pot in order to set the minimum/maximum position to fine tune. Please advise. I wanna make a number plate flipper for my bike with a servo. So On must be flipped up and off must be flipped down.
ACA	Simple Servo Controller	Sunday, July 03, 2011 9:38:42 AM
Question : can the other comparator be used to sense voltage drop in the vcc,and set different values for pin 6,as to make it switch H and V skew depending on receiver polarity?
ACA	Simple Servo Controller	Sunday, July 03, 2011 9:19:01 AM
I would like to suggest to add an IC where the pot is,and use the 13v/18v as reference to vary the resistance between 2 states for U1,in this way,you can feed the power from the LNB cable,and it will be possible to change skew according to polarity automatically.,with no power supply needed.
Arno	Simple Servo Controller	Wednesday, March 02, 2011 10:11:06 AM
Normaly, it will work with all kind of servo, maybe not with the digital ones..?!! But, like said in the comment uper, it is just a question of wire's color !
richard	Simple Servo Controller:::::question	Wednesday, December 29, 2010 7:36:24 PM
is it working in other servo motor or only in Futaba servos?
mrel	Simple Servo Controller	Saturday, November 06, 2010 8:39:55 PM
Schematic not to clear U1 (555) Is Capacitor C1 postive side connected Pin (1) and to Pin (2) and Pin (6) of U1 (555) chip? mrel
Fadil	Simple Servo Controller	Saturday, September 25, 2010 11:02:10 PM
Just like craig and john said earlier...I have the same problem too.All I need is to control the motor from 90 to 0 and 0 to 90.But my servo twitches once whenever I switch the circuit on.Please help me
Tony	Simple Servo Controller	Friday, August 06, 2010 2:14:50 PM
I hooked up the circuit on a proto board--it works pretty well, but I found it sort of noisy. In "Practical Electronics for Inventors," by Paul Scherz, it shows a 1000uF cap across the positive and negative inputs to the motor (page 933 of 2nd Edition). I tried a 5uF one and it cured the noise.