16F877A system and tachometer (FIS version) on the table

[mazoul72]

I have
Input pulsup (B5,B6,B7)
Input pulsdw
Input pulsres
and
Output mup (C3,C4,C5)
Output mdw
Output mres
High mup
High mdw
High mres

But it is the problem of 5V , no +12V . I don't understand ,+12V (output FIS) to +5V (output PIC) , it is a BIG problem ??

[mazoul72]

My program works like this :

a detection for RBx cause a different display to FIS Tachometer and for input isolator (output RC5,6,7) cause a +5V and +12V on output isolator .
BUT it is dangerous because a +12V on output isolator cause a failure on FIS tacho input voltage .
I would like only a No intrusive +12V but GROUND ONLY (action with ground input RBx) .
FIS give +12V in normal operation :

[aratti]

If your FIS tacho device doesn,t requires too much current at the inputs the opto is the solution ( remember that the signal is inverted. in other words when pic pin is low the output is high) I have separated the two grounds, but they can be common.

If on the other hand you will require more current at the input then use the second solution which uses two transistors.


Cheers

Al.

[mazoul72]

i put today +12V directly on FIS Tacho input , with harware power failure ...
What is the difference with +12V (10Kohms resistor) ??

Thanks for your answer ...

[mazoul72]

the 3 pins 23 / 24 / 25 on the FIS tacho.. are "on the fly" with 12V voltage .
Perhaps , with my 12V transformer (12V/300mA) , the inputs required more than 300mA that caused a power failure....

[aratti]

Can you post the data sheet of your tacho device?

Al.

[mazoul72]

How find it ?

it is a 1J5 920 846 C from golf4 .

[mazoul72]

If i put transistor directly to FIS without the +12V and 10Kohms resistors , i can have 12V from FIS (low level on PIC pin) and ground when transistor is "excited" .

[aratti]

Your FIS device has internal pullups, so you don't need the external one.

Cheers

Al.