need help to understand this circuit

[baha]

hello guys,
i'm newbie n still in progress to build my own robotic arm..
but im really not understand this schematic..
pliss anyone help me to understand this circuit..thanks!!

the circuit as below :

[Razor Concepts]

What do you not understand?


Basically what is going on is the PIC16F84 takes in data from the serial port, and uses that data to control servos.

[baha]

thanks bro..
what actually i wanted to know is the device use in that schematic..
n why they being use..im not actually really familiar with some electronic symbols.
from my understanding, there 2 power supply are connected,one for the circuit n another for servomotor.
it that true??

[Razor Concepts]

I don't know which symbol for the "device" you are talking about, there are a lot of parts in that schematic.

And yes there are two power supplies.

[baha]

sir can u name the device symbol that i label in square please..tq

pic below :

[SmAsH]

If you can't read anything let me know.

[baha]

thanks 4 the reply sir.

[baha]

crystal oscillator is use to control the timer/clock in micro controller.
am i right?

[SmAsH]

It controls the speed at which your microcontroller can do things.
http://www.societyofrobots.com/microcontroller_xtal.shtml

[baha]

what is the main function of 2 capacitors connected to the crystal??
 

[rgcustodio]

Open up the PIC16F84 datasheet:
http://ww1.microchip.com/downloads/en/devicedoc/35007b.pdf
Go to page 22. As per the manufacturer these caps are required. These requirements are not only for the PIC.


I found this very good PDF on the Net. Should be a nice read for everyone on how to use caps.
http://www.intersil.com/data/an/an1325.pdf

To learn more I suggest you take up engineering in college.

[Soeren]

Hi,

what is the main function of 2 capacitors connected to the crystal??

X-tal oscillators for microcontrollers use the parallel resonant mode of the x-tal and in that mode the x-tal needs the capacitive loading to oscillate.
If you want a precise frequency, the caps need to be selected carefully, or one of them can be replaced with a trimmer cap to be able to pull the frequency to the exact value (which will only be valid at one temperature).

The caps are not ment to remove noise. an x-tal oscillator needs a little noise to start, without it, the x.tal would only sit there and do nothing.

[gamefreak]

Cant we just say magic? Crystals are magic, but the magic cant function without specific capacitors to jump start it.

And quick question: Ceramic resonator VS Crystal+Caps, whats the difference?

So the above circuit uses a PIC microcontroller to interface some servos to a computer, it has a 4 MHz crystal but could be running at a lower speed with fuses. Has the commonly used 7805 voltage regulator to take 6 volts down to 5 and has a few capacitors to help smooth out the supply.

It would appear that the header socket causes a short circuit....

[baha]

yup,im using GUI to control my robot.

[Soeren]

Hi,

Cant we just say magic? Crystals are magic, but the magic cant function without specific capacitors to jump start it.

Sorry, I'm an engineer not a magician (although people around you sometimes demands you to be).
The "magic" in a crystal is just that it is a thin slice of piezoelectric quartz so (just like a human), it reacts to electric currents by bending. (We can therefore assume that people are semi-piezoelectric in their response, as they rarely give off voltage when bended).

And quick question: Ceramic resonator VS Crystal+Caps, whats the difference?

A ceramic resonator needs caps too, but they're integrated in the package in the 3 pin packages (with the 2 pin ceramic resonators you still need to add caps).

The difference...
Size: Piezoelectric ceramics can be manufactured in smaller packages than quartz.
Cost: They're is cheaper than piezoelectric quarts.
Mechanical strength: They're more rugged than a thin slice of quartz.
Electrical strength: They can handle larger fluctuations and faster rise times than quartz.
Precision: They can't touch the precision of quartz.

Comparing 2 standard through-hole components at room temperature (the Quarts in a regular HC49U housing):
Ceramics has a frequency tolerance of 0.5%.
Quartz on average 30 PPM (Parts Per Million), can be had in 5 PPM (that's 0.0005% or 10'000 times as precise).
There's a lot more parameters to the tolerance, but they all have this approximate difference.