data logging engine RPM with 10V logger

D

Don

Guest
Hi, I have a DataQ 194 data logger which has four +/- 10v input
channels. I want to log the RPM of a car, which is outputting approx
14volts. How can I reduce this voltage so the data logger does not go
up in smoke?

thanks
Don
 
Resistors.
1k

14V in----/\/\/\/----------- 7V out
|
|
/
\ 1k
/
\
|
_______________|_________
 
"JeffM" <jeffm_@email.com> wrote in message
news:f8b945bc.0310072110.20529953@posting.google.com...
Resistors.
1k

14V in----/\/\/\/----------- 7V out
|
|
/
\ 1k
/
\
|
_______________|_________
Click to expand...

That should work. However, you might want more isolation than that for other
reasons.

So, another possibility would be to use an optoisolator chip, like this one:

http://www.fairchildsemi.com/ds/4N/4N25-M.pdf

which you can get here:

http://www.allelectronics.com/cgi-bin/category.cgi?category=search&item=4N25&type=store

Use the chip like it describes in the test circuit in the datasheet.

Regards,
Bob Monsen
 
don@cameronsoftware.com (Don) wrote in message news:<11149158.0310071144.2ee00247@posting.google.com>...
Hi, I have a DataQ 194 data logger which has four +/- 10v input
channels. I want to log the RPM of a car, which is outputting approx
14volts. How can I reduce this voltage so the data logger does not go
up in smoke?

thanks
Don
Is the RPM reading an analog voltage? It seems that this value would
Click to expand...
be available as a frequency or pulse width.
 
Most automotive tachometer signals will be a pulse, either square wave or
sine wave with the frequency per RPM depending on number of cylinders and
whether two or four stroke (usually based on number of sparks per
revolution). Diesels & outboard boat motors are another story

Hope this helps,
Dennis

"Wade Hassler" <wadeh@neti.saber.net> wrote in message
news:d44d2251.0310090824.406143f3@posting.google.com...
don@cameronsoftware.com (Don) wrote in message
news:<11149158.0310071144.2ee00247@posting.google.com>...
Hi, I have a DataQ 194 data logger which has four +/- 10v input
channels. I want to log the RPM of a car, which is outputting approx
14volts. How can I reduce this voltage so the data logger does not go
up in smoke?

thanks
Don
Is the RPM reading an analog voltage? It seems that this value would
be available as a frequency or pulse width.
Click to expand...
 
What I am going to do is build a frequescy to voltage conversion
circuit using an LM2917. The circuit is simple and will output less
than 10V. A nice voltage graph will be better than looking at RPM
pulses to try to figure out the RPM.

Here is the spec on the LM2917:
http://www1.jaycar.com.au/images_uploaded/LM2907.PDF

thanks
d1
 
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