i have some futarba servos and need to controll them with electronics.

do i need a driver chip or can i do it some other way?

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when you post that reply, im just kidding.

 

I have used two 555 timer chips to make a driver. The first 555 is connected as an astable (free-running) oscillator operating at 50 Hz. The output feeds to the second 555 which is operating in monostable (one-shot) mode. The output pulse width of the one-shot is controlled by a variable dc voltage on the control voltage pin of the second 555. This analog voltage can come from a pot or from an D-to-A circuit, I've had good results with both.
Here's a link for a page which might help you:
http://www.seattlerobotics.org/guide/servos.html
It's a short tutorial on how the servos operate. They're actually rather easy to work with.
JB

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Nothing is impossible for the man who doesn't have to do it himself - Weiler's Law

 

do you have any drawings?

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when you post that reply, im just kidding.

 

Here's a circuit I've used. It works for me, but as I often say, your mileage may vary.
JB

Attached Thumbnails

 

__________________
Nothing is impossible for the man who doesn't have to do it himself - Weiler's Law

 

do you have to have to use the con voltage on the second 555 or can i put a cap on it instead? thanks for the drawing!

__________________
when you post that reply, im just kidding.

 

The control voltage applied to pin 5 of the second 555 dictates the pulse width of the output, which controls the position of the servo (ie. 2.5v= full left, 3v=center, 3.5v=full right, if I remember correctly). If you put a cap on pin 5 (like the first 555), you'll likely find that it [the servo] sits there and does nothing.
JB

__________________
Nothing is impossible for the man who doesn't have to do it himself - Weiler's Law

 

thanks, sorry i relizesd just after posting just one more thing. when i built it into to livewire a circuit simulater it doesnt work could it be the simulater?

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when you post that reply, im just kidding.

 

Don't know, never used the simulator. Maybe I (you) should let my friend know that your simulator says the servo drive circuit I built for him doesn't work ... :lol:
JB

__________________
Nothing is impossible for the man who doesn't have to do it himself - Weiler's Law

 

I know this thread is OLD, but I would like to try to build this board. I've already built a simpler one and it work, but doesn't work with digital servos.

Well. My question would be what caps do I use? polarized, np, ceramic, electrolytic? And what do I use to get a variable 2.5-3.5v input?

 

One could use a fairly simple adjustable voltage regulator for the control voltage, as seen on this page . Or I imagine a pot at the right value from this circuits +5v to ground, and the wiper on the wire expecting the control voltage might work. Just some ideas

 

Ok lets try actually getting the address to the page on it this time! Sorry about that.http://diyaudioprojects.com/Technica...gulator/]LM317 / LM338 / LM350 Voltage and Current Regulator Calculators[/url]

 

digital servos work on pulse width modulation. wouldn't work

 

Sorry I assumed you were speaking of the circuit mentioned earlier in the thread, that produces the control pulse modulation, varied by the control input voltage between 2 and 3.5v. No you are correct direct voltage on the signal wire of the servo wont work. I havent tried it yet myself, I hope to be able to
control brushless motor ESCs without the receiver. I am a new member so is telling me my post will be in a delay que.
voltage ragulator page is LM317 / LM338 / LM350 Voltage and Current Regulator Calculators
servo control ciricuit mentioned above is
http://www.electro-tech-online.com/a...s-servodrv.gif

Hope that helps.
Troy

 

I tried this circuit just today, and remember pin 8
needs GND (not in schematic). I couldn't get the control
voltage range indicated to keep my servo from far CCW
(I couldn't get it to move beyond "10 o'clock" at all). I
even tried the V all the way up to my supply (regulated
5v, so maybe that's why?). I altered the monostable's
capacitor, to no ideal, until I changed R4 to less resistance,
but I still couldn't get beyond "2 o'clock". It also made
"bottom out" noise at full CCW. All of this via diodes for
cutting the voltage down & testing 5V all the way to 2.6V.
BTW, I did get it to work however, by leaving in 3 diodes
in series to pin 5 of the monostable, and using a 4.7K
resistor in series with a 20K potentioneter for R4. In case
this is of any use and would like to control the servo by
resistance instead of V.

 

To which schematic does "this" refer?

If you are referring to the schematic using a 555, pin 8 is Vcc; pin 1 is ground.

John