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

 

[Jasen Betts]

On 2008-08-15, venkatraja999@yahoo.com <venkatraja999@yahoo.com> wrote:

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.

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.

hook a loudspeaker to pin3 (and ground) through 220 ohm resistor
(you should hear a buzz and the nature of the buzz should change as
you adjust the control)

Any ideas about what could be wrong ? How do i find the pulse
width ? ....

as a rough indication the LED's apparent brightness will change.

If you move the led a known fast speed the past a fixed scale the
pulses of light will appear to stretch... or you could use capture it
using a computers audio line in and view it on a "wave editor"
(eg: audacity)

but it's probably easier to replace the capacitor with one with
10000 times more capacitance and just use a stopwatch to measure it

if you don't have a resistor in series with the LED add one
(anything between 470 ohms and 2K should be fine there.)

Bye.
Jasen