Simple way to control servo directly?

This may seem an odd request for this group, since my application is different than in my R/C aircraft. But I want to build the simplest,
least complex signal generating source to feed one of my old retired servos, to make it move either in response to a potentiometer, or even simpler, to a toggle switch. It's been a while since I studied the "nuts and bolts" of the signal sent from our receivers to each channel's servo, and I have only a vague recollection of its form and nature.
I want to eliminate the radio link altogether, no xmtr nor receiver, just a simple wired connection (presumably 3 conductors) between my controller and the servo being controlled. To answer those wondering what I'm attempting - I want to use the servo to trip the shutter button on one of my digital cameras from a remote location, for taking wildlife photos from a blind. Remember - the simpler the better.
Olin McDaniel, W4PFZ, AMA 30932
To reply by email, please remove "abcd" from Return address ----------------------------------------------------- "Ignorance is treatable, Stupidity is incurable. Sometimes the difference is hardly distinguishable, however."
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You need a circuit that generates repeated pulses between 1 and 2 milliseconds long (1.5 being the mid-position of the servo). The other 2 wires to the servo are the negative and positive power supply (between 4.8 and 6v).
This is a pretty simple circuit that uses a single 555 chip and an inverter:
http://soli.inav.net/~fox/fursuit/servo.jpg
Otherwise, I'd suggest Googling a bit - wired R/C servo control is a very common application.
Russ.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Thanks Russ. I checked out the picture (schematic) as referred, and I might try building up the gadget shown. Haven't done much electronic building lately, need to oil up my rusty techniques and this might be just the ticket. However, the other post about buying a "servo tester" for $15 probably is the more sensible option. But who ever said we gotta be sensible, especially when I spend hours hunkered down in a blind, getting eaten by mosquitoes, etc. while trying to capture a picture of some fleeting bird or deer or? ?
Olin
To reply by email, please remove "abcd" from Return address ----------------------------------------------------- "Ignorance is treatable, Stupidity is incurable. Sometimes the difference is hardly distinguishable, however."
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Buy a servo tester from Astroflight for $15.
--
Normen Strobel
snipped-for-privacy@zoominternet.nospam.net
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Great idea, thanks for the suggestion Norm. I just looked in the latest issue of Model Aviation for that outfit, but they aren't listed at least this month. Will do a google search for them next.
Olin
On Sun, 7 Sep 2003 09:48:14 -0400, "Normen Strobel"

To reply by email, please remove "abcd" from Return address ----------------------------------------------------- "Ignorance is treatable, Stupidity is incurable. Sometimes the difference is hardly distinguishable, however."
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 07 Sep 2003 16:15:26 GMT, snipped-for-privacy@mindspring.com (Olin K. McDaniel) wrote:

http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXVK79&P=7
If you just gotts to get solder smoke in yer eyes, surf to Tony van Roon's site has a few servo tester circuits which should serve nicely http://www.uoguelph.ca/~antoon/gadgets/gadgets.htm
Cheers, Fred McClellan the dash plumber at mindspring dot com
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Followup to all interested and helpful comments - I followed Norm's suggestion and ordered the servo tester from AstroFlight. It just arrived today, and does the job very well. Saves me a lot of wasted time, cutting and soldering, etc. The price was actually $19.95, but that included shipping the nearly 3000 miles across country. It works equally well with almost any make of servo, and with standard control surface servo as well as retract servo. Just what I wanted. Thanks to all.
Olin
On Sun, 07 Sep 2003 16:15:26 GMT, snipped-for-privacy@mindspring.com (Olin K. McDaniel) wrote:

To reply by email, please remove "abcd" from Return address ----------------------------------------------------- "Ignorance is treatable, Stupidity is incurable. Sometimes the difference is hardly distinguishable, however."
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Hi Olin
It seems to me that you are intending to do it the hard way - why use a servo at all? The usual and easy way is to use a solenoid - just wire it up and use a simple push-on sw to operate the shutter - cheap as chips and twice as easy!
David
"Olin K. McDaniel" wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I used to take wildlife photos also using a remote set up.
On the first attempt I tried a solenoid but ran into wire lenght problems, ie the voltage drop across the wire was so great it prevented the solenoid from operating. You may run across the same problem with a direct servo controller, depending on how far away you want to get from your camera.
Thought about using my airplane TX/RX setup, but then I realized that the frequency was not allocated for this use, so I ended up buying an cheap RF camera remote for $50 or so, which I felt I should have done from the start!
This was about 20 years ago, so apologies for not having a source of the remote I bought, but just thought I'd put in my "2 cents"
However you do this, I wish you good luck!-)
Regards,
Frank
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
A relay would solve the wire length problem. Mount the batteries at the camera site and trigger the relay remotely.
--
Paul McIntosh
Desert Sky Model Aviation
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
How about just making your original solenoid work?
All you have to do is increase your battery voltage to overcome the voltage drop in the long cable.
Not the most efficient solution, but it will work.
Mike
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Exador wrote:

An even easier one is to use FAT CABLE. Somethiung like what you use for car audio speaker wiring.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.