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Help point me in the right direction, servo controllers

I need some electronic circuitry help.  I'm building a door.  The door is going to be controlled by one servo.  I am trying to get it so that by pressing one button it goes to the open position and by pressing another button it goes to the close position.  How would I go about doing this?  I've been reading up like crazy about lm555 circuits and controllers but I just don't know how to apply that, if it's even possible.

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The easy approach might be just to use a small PICAXE. Have a look at http://www.rev-ed.co.uk/docs/picaxe_manual3.pdf (page 19).

Well, it's more like a garage door and it's tiny.  I won't have room for a limit switch, so that's out of the possibility.  I was really hoping not to use a picaxe, just for cleanliness reasons and it's more money than I want to shell out.

I was reading about a circuit that uses an lm555 and you can use a pot to set the location of the servo.  http://www.hvlabs.com/555servo.html  Is that at all what this is or am I just reading it wrong?

Anyway, if I'm right, I was wondering if I could build two of these and replace the pot on each one with a resistor that puts the servo in exactly the place I want it.  One circuit could be for "open" and the other for "shut", then I'd just have to activate the circuit.  Am I at all on the right track?

give some more information about the physical size. So, people here could give you more solid, useful answers?

I have all the room in the world for circuitry, I just might not have room for physical switches and things.  So, aside from a limit switch, it's not really relevant or worth my explanation.

Here's what I want to do:  One on-off switch that, when pushed in, closes the door and, when pulled out, opens the door.  I suppose I will use two switches, one to detect when it's open and one to detect when it's closed.  If the switch is pushed in and the door is pulled open, the motor needs to turn back on and push it back closed.  If the switch is pulled out and the door is pushed shut, the motor needs to turn on and pull it back open.

I can figure all that out.  However, the problem is telling the motor to spin backwards or forwards.  If I used a regular motor I could easily use relays to change polarity, but I still want to use a servo.  I know almost nothing about servos, how could I do this?  (preferably without a picaxe)

Servos are not reversed by changing polarity, merely by changing the signal on the signal wire.

Basically the pulse signal is designed to be between 1 and 2ms,  At 1ms the servo fully rotates in one direction to the limit of travel and stops and at 2ms it fully rotates in the other direction before stopping.  At 1.5ms the servo stays stationary at the mid point of travel.


All RC servos generally use this convention.



Would my best bet just be avoiding that and getting a DC motor and gearbox?

Actually, would it be possible to save money by taking apart the servo and removing the circuitry and just using it for the motor and gearbox?

I started thinking about something I saw at HackADay. http://hackaweek.com/hacks/?p=153

Watch the video clip at the bottom.


Could someone look over this schematic and see if I made any errors?  Sorry for the sloppiness, I made it on graph paper by hand first but can't scan it.  I know it's a simple circuit, but I just need someone to check it, please.


1. SPDT Toggle Switch - User decides which way motor rotates

2. SPST Momentary Switch, normally closed - Stops the motor after rotating for so long

3. SPST Momentary Switch, normally closed - Stops the motor after rotating for so long

4. DPDT Relay - Reverses polarity of the motor

5. Motor


The goal of this circuit is to turn the motor one way when the toggle switch, 1, is turned to the first position, until the momentary switch is depressed, 2.  When the toggle switch, 1, is turned to the second position, the motor should rotate the other way until the momentary switch is depressed.


Sorry to interject a new idea here, but have you considered a solenoid? These come in push or pull types with various range of motion. Usually the motion is only an inch or less. Some solenoids come with a spring to return it to postion when it is unpowered.

You don't need any gearing or fancy electronics. One position will keep your door latched and closed. Power the solenoid (probably through a relay) and it opens the latch to let the door open for as long as you hold the button.

If you need a delay, you could use a 555 one shot circuit to create a pulse of the desired duration when you press the button. This pulse powers the relay, which turns on the solenoid.