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Q.I have read with interest your reply in the May
edition of SERVO regarding inexpensive microcontrollers. An alternative your reader might like to
consider is the PICAXE system. These are PIC chips with
bootloaders installed. They are programmed using a free
Basic editor and the programming circuit consists of nothing
more than two resistors. They are surprisingly powerful with
the higher end products, sporting up to eight servos or two
pwm lines operating in the background. Details can be found
I have no connection with this company other than that
of a satisfied customer and devotee.
microcontrollers, electronics, and robots. They currently offer
seven different microcontrollers with 5 to 32 lines of I/O control.
The cost for the PICAXE microcontrollers is slightly more
expensive than that of bare PIC microcontrollers. These prices
— along with the free Basic compiler — make the PICAXE
microcontroller the least expensive option for the hobbyist.
— James Carter
via Internet (UK)
A. Thanks for the note. After I received your Email, I went
to their website to check them out. I was quite
impressed with them. The Basic compiler is free, can be
downloaded from their website, and has all the features you
need to be able to program the microcontroller to do whatever you want it to do. All you need is a simple three wire
serial programming cable (that you can purchase or build
yourself) to program the PICAXE microcontrollers.
They have some excellent documentation on their
website that shows you how to use their products, along
with some excellent tutorials for learning how to use
Q.I have a robot that is controlled by a laptop computer.
I’m using external speakers so that I can hear the
robot talk when the screen is closed. The problem
that I am having is that when I power up the servos, I can
hear the noise of the servos through the speakers.
The board used to control the servos is a USB Servo II
by ACS. The power jack to the servo control board also powers
the speaker amp. Is there anything I can put between the
jack and the amp to stop this noise? Do I have to put them
on a separate power supply?
— Wone Barnwell
A.As a general rule of thumb, electric motors should
always be connected to a separate power supply, since
they are notorious sources of electrical noise. When
using two separate power supplies, make sure that both of
the grounds are tied together, so that all the electronics are
using the same ground reference, or
you will see erratic behavior in the
components. If you have to use the
same power supply, then try adding
some 0.1 µF capacitors between the
positive and ground wires as close to
the servos as possible.
The best way to eliminate the
noise from the servos is to completely
isolate them from the rest of the
circuit. This also means using two
separate power sources (one for the
Figure 1. Servo optical isolation circuit example.
+ 4.8 - 6.0V SERVO POWER
FROM ORIGINAL SERVO
SERVO CONTROL SIGNAL
CONTROL ELECTRONICS GROUND
OP TICAL ISOLA TOR
i. e. PS2501-2
46 SERVO 07.2004