tach input

[Grant Beattie]

On Mon, 21 Oct 1996, Krister Wikstrom wrote:

Some really great and helpful stuff, thanks.

> I have used opto-isolator, and didn't have any problems. I found an 
> old 4N25 opto, put two resistors in series, and a zener diode from 
> between the resistors to the other side of the input diode - the first 
> resistor limits the current to the zener (I used 15V), and the next one 
> sets the max current to the opto input.

I guess I was a little vague.  The only peice of info I'm missing is 
what's the original input voltage?  You have a 15v zener that limits the 
voltage excursions and an input resistor as well.  So if the voltage on 
the zener is 15v, what's the voltage on the input res?


Mystery
input
voltage       R1             R2

   0--------WWWW-----------WWWWW------ opto
                      |
                      | /
                     ---
                    / ^   Zener
                     / \
                     ---
                      |
                      |
                     ===
                      -

GB