Topics Topics Edit Profile Profile Help/Instructions Help Member List Member List  
Search Last 1|3|7 Days Search Search Tree View Tree View  

Driving a Servo with a 555 IC

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2007-2009 » Archive through 28 November, 2008 » Driving a Servo with a 555 IC « Previous Next »

  Thread Last Poster Posts Pages Last Post
  ClosedClosed: New threads not accepted on this page        

Author Message
Top of pagePrevious messageNext messageBottom of page Link to this message

neroku
Regular Contributor
Username: neroku

Post Number: 40
Registered: 09-2007


Rating: N/A
Votes: 0 (Vote!)

Posted on Monday, 20 October, 2008 - 11:53 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi out, I want to keep a servo operating just in two different positions. I achieve this using two 555 IC. Each 555 provides a PWM signal (thus two "positions"). I need to switch the signal input of the servo between the two 555 outputs.
How do you recommed doing this switching?

I think using a bipolar transistor or a relay will do.


TIA
I have my own way of doing things
Top of pagePrevious messageNext messageBottom of page Link to this message

davy
Regular Contributor
Username: davy

Post Number: 42
Registered: 06-2005

Rating: N/A
Votes: 0 (Vote!)

Posted on Tuesday, 21 October, 2008 - 08:47 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

A more elegant solution would be to use a single PIC.
The software would give you 2 positions for the servo triggered by one of the pins on the PIC.

Davy
Top of pagePrevious messageNext messageBottom of page Link to this message

joe
Frequent Contributor
Username: joe

Post Number: 491
Registered: 05-2005

Rating: N/A
Votes: 0 (Vote!)

Posted on Tuesday, 21 October, 2008 - 09:02 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

If you really want to use a 555, then how about using just one 555 but switching in/out the timing capacitor / resistor ?
Would save you a 555

Joe
Do one thing each day that scares you – work here !
Top of pagePrevious messageNext messageBottom of page Link to this message

neroku
Regular Contributor
Username: neroku

Post Number: 41
Registered: 09-2007


Rating: N/A
Votes: 0 (Vote!)

Posted on Tuesday, 21 October, 2008 - 11:13 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi Joe, switching in/out the timing capacitor/resistor will change the PWM signal period. I need to change the width of the PWM signal, but the period must be kept constant in order to work properly.
I have my own way of doing things
Top of pagePrevious messageNext messageBottom of page Link to this message

stylers
Frequent Contributor
Username: stylers

Post Number: 145
Registered: 04-2005

Rating: N/A
Votes: 0 (Vote!)

Posted on Tuesday, 21 October, 2008 - 01:35 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

there is a way of doing this with a 555 I think, involving inversely connected diodes in the RC circuit.. there are plenty of 555 timer servo controllers on the web, it should be possible to avoid using a PIC in this case..
Top of pagePrevious messageNext messageBottom of page Link to this message

gajjer
Frequent Contributor
Username: gajjer

Post Number: 154
Registered: 05-2007

Rating: N/A
Votes: 0 (Vote!)

Posted on Tuesday, 21 October, 2008 - 06:07 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi Neroku
joe is right, you can do it by just changing the timing resistor. The period does change a small amount but it is not important. I've done it and it works.
It seems that the tolerance on the servo period is very wide. I believe it can be anywhere between 10mS and 20mS. The important thing is the timing pulse width.
I am always up for a PIC solution but it is just unnecessary for this application.

cheers
gaj
Top of pagePrevious messageNext messageBottom of page Link to this message

obiwan
Frequent Contributor
Username: obiwan

Post Number: 2370
Registered: 12-2005

Rating: N/A
Votes: 0 (Vote!)

Posted on Friday, 24 October, 2008 - 01:21 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Just a couple logic gates would do the trick....

Then you have two independent frequencies that you can adjust. You have one input, high and low.

POC (piece of cake)

I leave the simple solution up to you.

(Message edited by obiwan on 24 October, 2008)
Do Not Hit The Fly That Lands On The Tigers Head.
Top of pagePrevious messageNext messageBottom of page Link to this message

neroku
Regular Contributor
Username: neroku

Post Number: 42
Registered: 09-2007


Rating: N/A
Votes: 0 (Vote!)

Posted on Sunday, 09 November, 2008 - 10:51 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

In response to my own question:

Using a two channel analog multiplexer like the 4053 one will make my life quite easier.

Thank you all
I have my own way of doing things
Top of pagePrevious messageNext messageBottom of page Link to this message

winston
Frequent Contributor
Username: winston

Post Number: 163
Registered: 02-2007

Rating: N/A
Votes: 0 (Vote!)

Posted on Wednesday, 12 November, 2008 - 02:50 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Note that you can change the duty cycle of a 555 timer very easily by changing the voltage at pin 5 (the control pin). Pin 5 is often overlooked, but it's very useful.

Administration Administration Log Out Log Out   Previous Page Previous Page Next Page Next Page