Control a Servo Motor Without Programming

By Jonathan Best
Time Required: 30 minutes
Difficulty: Moderate

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Control a Servo Motor Without Programming

I am going to guide you through the process of making a circuit that will allow you to control a servo by turning a dial. At the same time I will explain what is going on in the circuit and how it works.

Steps

Step #1:

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A servo motor is controlled by sending a series of pulses to it. This is called "pulse width modulation." Depending on the length of the pulse it will turn to a specific angle.
A pulse must be sent to the servo every 20 milliseconds. The pulse length will vary from 0.5ms to 2ms. If it is 0.5ms the servo will turn as far as it can anti-clockwise. If it is 2ms it will turn as far as it can clockwise.
By using a pulse-generating circuit controlled by a potentiometer any pulse length between 0.5ms and 2.0ms can be sent to the servo. This allows us to move the servo arm to any position desired.

Jonathan Best

Jonathan Best

Hey, am very sorry I missed that out, this is the first guide I have made.

The positive lead from the battery goes to the right hand terminal where it has 0v/6v written beneath it.

Hope that helps,

John
Jonathan Best

Not that I can definitely say. Try putting two servos in parallel on the output.
Sorry I couldn’t be of more help.
Jonathan Best

I don’t have the file on my computer at the moment (at university and it is at home), sorry.
Tom

Google ‘555 timer servo controller pcb layout’
David Hdez Moreno

Hi, where is the potentiometer? I need to control a servomotor that allows up to 36 V DC. Do this circuit works for it too?

How are connected the pins of the servo?

Regards :)
Ben Brown

Regarding the 555 timer servo control circuit. How could I replace the control pot with a SPDT momentary switch? I’m not sure how it would wire into the circuit. Thanks Ben Brown
Louie Lalaguna

can i use another 555 timer, and not the NE-555N?
ramesh

sir i used 555 timer for generating pulse with modulation…im using 470k pot for varying the pulse width..im using vts-08B servo motor…..im not able to run the servo motor
Dvizma Sinha

Hi,

Can this circuit work with continuous rotation servo motor?
John

I´ve probed this circuit several times and DOES NOT WORK !!. So, don´t waste your time. Cheers, John.
Dinesh

Please send me any driver circuit schematic for Servo motor.
Hakeeq Javid Shaikh

does this control the speed of servo motor or does it controls the position ???….. i mean if we rotate the potentiometer then the servo meter will also rotate the exact distance that was moved by the potentiometer???? is it so ??
- Sky Blue
  
  It controls the position. The speed is constant. If you quickly turn the potentiometer really fast, the servo will turn to the position, but at [its] lower, constant speed.
Hakeeq Javid Shaikh

what type of capacitor is used…… i’m not getting wat type of capacitor is used….. pls tell me…… email id: [email protected]
- Sky Blue
  
  Capacitor 1: 10 microfarad
  Capacitor 2: 100 microfarad
  - CJ
    
    nanofarad….
Alexa Beers

What are those green wires called that you hooked up to the joy stick?? Also, can you name off all the things in this project that you bought? Or have in it so I can do my science project
- Sky Blue
  
  1. It isn’t a joystick, it’s a potentiometer.
  2. Here is the parts list:
  > 1x NE555 Timer IC
  > 1x Rectifying diode
  > 2x 1N4148 diodes
  > 5x resistors (10K, 20K, 180K, 220, 470, value is in ohms)
  > 2x capacitors (10, 100, value is in microfarad)
  > A bunch of jumper wires
  > 2x blue screw pin terminal
  > 1x 8 volt power source
  > 1x PCB or Breadboard
  3. Good luck, and have fun on your science project! ;D
  - Rolland Elliott
    
    what is a good place to buy all these components online. I want to make about 50 of these and since I’m new to electronics dont’ want to over pay.
  - Rolland Elliott
    
    is there any company that sells a premade kit? I found one on servocity’ swebsite but $80 is kind of expensive given these components are probably around $10?
Subhadeep Aich

can’t we control the speed without programing
Kevin Dearing

So, I’m really new to electronics.. My question is, when the Pot is set to a particular setting the servo will mote to the corresponding position and stay there. But it the signal continuing to be sent to the servo? If the signal is still being sent to the servo does it drift some? I’m guessing with the right capacitor and diode that should be somewhat easy (but not for me since I’m basically clueless). If there is no drift then I guess it’s not that bad but I’d still like to preserve energy anywhere I can.

I’m really asking this because i want to use your circuit as a basis for a 2 position servo that I want to make. I would have to add a relay or something to the circuit to switch from one position to the other. The pots I plan to use will be the small ones you tweak with a screwdriver so they won’t be changed once they are set.
- CJ
  
  In this circuit, the pulse train is sent continuously – the motor stops moving after it reaches its commanded position, but the pulses never stop. If everything were perfect, the motor would keep perfectly still at this point.
  
  As you observed the pulse train is not perfectly uniform, and there will be slight variations in the pulse widths (jitter) from one pulse to the next, and/or long term drift, due to noise, temperature changes and other factors. The motor may interpret these variations as move commands and slowly drift, or dance back and forth slightly.
  
  My understand is that servo motors have a built-in dead band, which can be modified with a servo motor controller, that is intended to prevent these oscillations.
  
  If you disable the pulse train, then the servo will stop hunting (some shut down completely, some just maintain the most recently commanded position). Disable the pulse train by disconnecting pin 4 of the 555 from VCC (pin 8) and connecting it to Ground (pin 1) instead. To restart the pulses, reverse these steps. Don’t short pins 1 and 8 together, as that would short out the power supply
  
  Of course you’ll have to come up with a method of stopping and starting the pulse train at the appropriate times.
Dylan Hale

Will this draw power from the battery when the potentiometer isn’t being rotated?
- CJ
  
  Yes it will, the oscillator will continue to run and generate the pulse train. Also, the motor will dissipate some quiescent power. The motor may occasionally twitch due to jitter in the pulse train, and that will also consume power.
Barron Anderson

Thank you Mr. Best for this tutorial. I am a beginner and this is almost exactly what I need for a project I am embarking upon. Sorry for noobie questions but here goes…

In Step 3 you show your schematic, where is the potentiometer in this diagram?

Best Regards,

B. Anderson
- CJ
  
  The resistor on the right labeled “20K” is a potentiometer. The wiper is indicated by the triangle in the center of the resistor.
Barron Anderson

When looking at the schematic, when lines intersect does that imply a circuit junction point, or is a blue dot used exclusively to represent a junction, and lines intersecting are merely an inconvenience of describing a 3D object in a 2D space/picture?
- CJ
  
  Where lines cross without a dot, the lines are not connected.
Barron Anderson

The Diagram shows 0.5ms to point to the left. Is this 0.5 micro or milli seconds?
- CJ
  
  .5 milli seconds, .005 seconds
Yash Patil

What type of capacitors are used? I mean electrolytic or polyster or some other.
- CJ
  
  For the values in this circuit, ceramic is appropriate. You can use any type of capacitor that comes in the right value. BTW 100nF is the same as .1uF, 10nF is .01uF
Massive

I am going to try this because I need to start somewhere. But, is there some kind of cheap controller one can get that controls position and speed? There are a lot of things out there, like sewing machines, that are now run by servos that control position and speed. But most of the motors are very expensive and often weigh more than the machine itself, say over 20 pounds.
Rudy Mendoza

Great useful tutorial!! But I can’t discern how the 2 blue screw pin terminals are used/connected – can someone please help. Thanks…
- CJ
  
  There are two terminal blocks, one with two screws and one with three.
  
  The one with two screws connects to your power supply to power to the circuit – GND to the “0V” screw and 6V to the “6V’ screw.
  
  The terminal block with three screws connects to the servo motor. In this diagram, the left screw goes to the motor’s signal wire (white or yellow), the center screw goes to its Ground wire (black), and the right screw goes to its Power wire (red).
Cappello Manch

Thanks for the brilliant tutorial. I need to know if this method can be used to steer RC car wheels? As in can it rotate left and right or does it just rotate in one direction?
Thanks.
shamz rock kapak

Im looking for 7.5k ohms potentiometer rotary..malaysia market only have 5k ohms..what happen if im using 10k..is it servo still working? I need some help..
michael daniel

What type of rectifying diode are you using?
noteven close

Hello, Im looking to have my servo merely turn at 3600 rpm at a relatively constant basis while also getting a nm of 34. Is there something I can do to achieve that without the amp/driver. It is rated for that type of performance. Hope you can enlighten me as Im kind of green on these motors. Thank you for your knowledge…

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