Servo Control Problem

Hi,
Newbie question.
I have made a servo control circuit and it does not work. It will be
very nice if someone in this NG can help.
-------------------------------------------------

SERVO: Sanwa, SRM 102, 6 volts, 3.3 Kg-cm torque;

Leads are black,red and blue. I am assuming them to be ground, +ve,
signal.
If I switch on the power with out connecting the signal wire, (a) it
moves to the left if it is not already there.
(b) If it is already there, then there is no movement.


If I connect the signal there is no change in the behaviour of the
servo. It is like in a, b above.

---------------------------------------------------
Circuit: It is by tony von roon

(http://www.uoguelph.ca/~antoon/gadgets/servo1.htm

Even though I could access this page yesterday, today it is giving
"404 not found" error)


Anyway the circuit schematic is very unlikely to be wrong, so the
problem ought to be in my implementation...


It is a circuit based on the 555 chip, to generate 1ms to 2 ms
pulses.
The output is routed via a transistor.
I have put a LED on output ( pin no 3 ) of the 555 chip and it
glows when i switch on the circuit.

I dont have a oscilloscope nor do i have a frequency counter.
---------------------------------------------------

Any ideas about what could be wrong ? How do i find the pulse
width ? ....
Please note that I am a beginner in electronics.
Thanks in advance.
Venks

 

[Rich Webb]

On Fri, 15 Aug 2008 08:48:56 -0700 (PDT), venkatraja999@yahoo.com wrote:

It is a circuit based on the 555 chip, to generate 1ms to 2 ms
pulses.
The output is routed via a transistor.
I have put a LED on output ( pin no 3 ) of the 555 chip and it
glows when i switch on the circuit.

I dont have a oscilloscope nor do i have a frequency counter.
---------------------------------------------------

Any ideas about what could be wrong ? How do i find the pulse
width ? ....
Please note that I am a beginner in electronics.

Hard to recommend an approach without knowing what you can get your
hands on. An obvious solution would be a gated counter, either a
dedicated counter chip or a counter/timer inside a microcontroller.

--
Rich Webb Norfolk, VA

 

[Tim Duke]

SERVO: Sanwa, SRM 102, 6 volts, 3.3 Kg-cm torque;

Leads are black,red and blue. I am assuming them to be ground, +ve,
signal.
If I switch on the power with out connecting the signal wire, (a) it
moves to the left if it is not already there.
(b) If it is already there, then there is no movement.

The servo should not move at all if you only connect the +ve and -ve. You
may have a faulty servo.

The length of the pulse determines the position of the servo - approx 0.8mS
at one extreme and around 2.2mS at the other. 1.5mS should be approx.
middle. Each pulse should be separated with a low of approx 20mS. Although
longer than this just means that the servo takes longer to reach its
position.

If you are connecting all three wires, then it looks like you are getting
pulses out from the circuit (is it similar to this one?
http://www.uoguelph.ca/~antoon/gadgets/servo2.htm).

If it is similar, you may want to play around with the value of R2.


Tim