REV counter using PIC16F877

[fever]

hello all,
last moth i succeeded in making a tachometer for my car.i used LM2917 and LM3914 as the f-v converter and LED driver.
this time i want it for my motorcycle.as the indicator panel is quite small,i want to make the tacho circuit quite compact.
while searching i came across this site,where i found the TACHO built by PIC16f877.
**broken link removed**
iam not very good at PIC stuff.
can you guys clarify my doubts.
1.can i use pic16f877A instead of 16f877.what does this A stand for?
2.in the LM2917 circuit,i used some resistors and capacitors at the frequency input.(for filtration i guess ).but this circuit uses only a pot is it safe?
3.in the circuit pin 1 is directly connected to 5vdc.i think it shld be coupled by 10k resistor.am i right?
4.the LEDs are connected in sourcing method(common ground).how can i change it back to sinking connection(supply common).so that it will protect the PIC
5.the author said the pot has to be adjusted so that MAX 5v should come in.how can i do that.

sorry if my questions are too long.pls help me clarify the doubts.
i'll be thankful.
regards

 

[matc]

1. The A part is a revised part. I believe not much is different, but the code protection fuse is the other way round? Anyway, your software should handle both parts the same just fine.
2. No idea...
3. Reset line? Should be safe to link to VCC, check the datasheet.
4. How will that protect the PIC ?
5. The issue you have is that going much over VCC or under GND can cause latchup in most digital parts. This is v. bad. Best to connect signals via a protection resistor (eg 1k) and include protection diodes to VCC and GND.

 

[fever]

thanks for the reply.
4.in sourcing connections,led will try to draw the current from he PIC.if some thing goes wrong the amount of current will become more and this will burn out the PIC.where as in sinking mode,we try to sink the current in to the PLC.one can sink 5 times more current in sink thank in sourceing.
5.so i should connect a resistor in series with pot and give diode protection(to protect from reverse polarity?) can u explain this part a little more.

thanks once again.

 

[fever]

any more comments on the circuit ?

 

[fever]

i build the circuit yesterday.
when i switch on the power(+5v) all the LED's are ON,when there is no connection to signal input pin(2).so i connected it to my bikes ignition system VIA a 15k resistor(it works on CDI system and there is a wire thru which i get some voltage when i increase the RPM) the LED are gone.

when i increase the RPM all LED's are just flickering.
one thing i don't understand is,will the code counts the pulses and lit the LED's according to it? or it just do the job of LM3914.

iam stuck at this point.can you guys help me?