general questions about pic microcontroller

[TTU.ABD]

I have three question about pic microcontroller :
1- When I the connect the output voltage of regulater 5V to pic , the voltage drop to
half as shown in the lower, why?



2- is conduction in above right?
nor I must connect the output of regulater 5 volt (7805) to pin digital input
on pic 16F88 and to ( resistor and ground ) as shown in the lower ?



3- finally , can I connect crystal to pic16f88 without capacitors?

 

[alec_t]

1) and 2) A voltmeter should be connected across (i.e. in parallel with) the voltage source to be measured. Your meter is in series between the 7805 output and the micro pin.
2) In the second pic the 5V connection is fine, but your switch will need to be debounced (in software, or by using additional components).
3) Read the datasheet for the micro and follow its guidance about capacitors.

Edit: The input voltage to a 7805 needs to be > 7V for it to regulate properly. Your LED is dropping the voltage too much. Run the 9V directly to the 7805 input.

 

[Vizier87]

3- finally , can I connect crystal to pic16f88 without capacitors?

In addition to what has been suggested, the PIC usually would still operate without the caps. It's only a question of stability. You will see the difference when you operate the PIC with or without the caps.

At least from my experience.

Cheers.

 

[TTU.ABD]

internal resistance of pic



I observe the pic has very high internal resistance , so Why do I have to put resistance 10k ohm ?

 

[Ian Rogers]

That chip can work without the crystal as well.. This chip has an internal settable up to 8mhz crystal..

The port can sink up to a maximum of 25mA.. So a 200Ω resistor is about the smallest you could go for....
( There are other rules to be obeyed, the port as a whole can only sink 100mA)