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Operate a servo without a microcontroller ?

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mbryson

New Member
Hello,

I am a beginner in electronic. I am learning Arduino and I loved it. But I find the use of a microcontroller for very small project is just overkill.

I would like to operate a 6V servo on 90 degree only with the less components possible. Is there a way to send pulse to the motor with a simple electronic circuit? The power is a 12V motorcycle battery.

I am interested in the "how" but even more in the "why" :)

Thank you

Martin
 

bigkim100

Banned
I have actually built this circuit, provided by Blueroom, and it really works well. I used it for a eye blink mechanism, and 2 axis eye movement in a prosthetic head, and it really did the trick, and is simple to make. You will need to include a 5 or 6v regulator to run it off of 12 v tho
 
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Sceadwian

Banned
Less components as possible hmm?
A single 8 pin micro controller would be able to do the same thing.
My favorite thing for stuff like this was the tiny11. Unfortunately it was discontinued.
 

Mr RB

Well-Known Member
You can do it with one 555 timer... Why use 2?

If you drive the 555 sense pins from the output pin3 (and leave pin 7 disconnected) you can separate charge and discharge times with 2 diodes, so you can pick any HI and LO periods. Then use a pot in the charge diode loop to adjust the HI time period, the LO period will remain stable.
 

mbryson

New Member
I am stuck in my homework

Ok... So I did build the circuit and my servo only turns when I disconnect the white ( control) wire. It turns by shots of ±15 deg. or more CW and occasionally CCW until it reaches the physical limit, then it just bumps the limit.

The power supply gives 6.31v at 1A it drops down at 6.29 if I jiggle the motor. I tried with a 7805 regulator but I always get the same result.

I couldn't find any 31k so I put a 30.1k resistor

I noticed that If I touch the control wire when it is unwired with my finger it turns CW all the way to the limit.

Is that all that this circuit can do ? Or did I made a mistake somewhere ?

Ideally I would like to be able to go CW and CCW with the push of a button and have a led monitor on the two sides, but first I would like to make this thing work.

Thank you for your help
 

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mneary

New Member
You have miswired the potentiometers. The 7500 ohm resistor from the IC to the left pot pin 3 is correct. The center pin of the first (left pot) should not be grounded. It should go to pin 3 of the right pot. Then the middle pin of the right pot should go to pins 6 & 7 of the IC and the capacitor. Pin 1 of both pot should be free. No potentiometer pins are connected to 0V.

You may need 100µF or more across the red/black of the servo to keep the junk from servos getting back into the 555's.
Hooking the R lines of the 555s to the + supplies could help.
Putting 0.1µF from the CV pins on the 555s to 0V could help.
Putting 0.1µF from each 555 pin 8 to pin 1 could help.

[edit] I wanted to add what a pleasure it is to help troubleshoot with such a clear photo. It shows that you respect those that are offering help..
 
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mbryson

New Member
Its working !!

So after a few hours here is a pic of my more crowded board. I didnt hook pin 5 to ground because it was not working. I did add the few capacitors that you suggested.

I added a 7806 regulator circuit @ 1.5A maybe a bit too much for the motor ?

I added one more pot to have the 0 ohms and the 5k ohms on separate circuits on my switch. Now that I know the values I will replace all pots with fixed resistors.

Now I would like to have the red led lighten when the motor is turning on one side and that its stays on. It would shut off when I make the motor turn the other way. Is there some sort of diode that can keep a state and feed the led and then shut off when I send a signal again ?

Aftertought : Its a good exercice and I want to get through it but since I wont do a million of those I am tempted to do it with the Arduino board ( Atmel mega328 microcontroller ) Through programming I will be able to do a closer control of the the led and motor and add more stuff :D

YouTube - P1020557 1

I want to thank you all for your precious help. It really gives the spark...:)
 

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Sceadwian

Banned
Nothing like a working project =)
It's good to play around with circuits like this but if you're going to be moving on to micro controllers I would skip a lot of this stuff although it does give some practical knowledge on constructing things. An Arduino can directly control the servo's without any additional circuitry and with buffer drivers it can drive pretty much anything else as well.
 
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