Hi Finn;
It is a CMOS device capable of handling 20vdc on
its VDD pin. So I didn't feel it was necessary. In reality I found it was
unstable when VDD was less than 5vdc or greater than 11vdc, so since I had
a bag of 470ohm resistors handy, I just put a voltage divider on the VDD.
With a regulated 13.8vdc it gives me just under 7 volts and a stable reading.
a side note; I originally had an internally
regulated alternator but the regulator failed (have since converted to an
external reg as per "electric Bob"). When running with the alternator tripped
and less than 12vdc, I found the tach would become erratic at high RPM's,
due to a low VDD. When alt is charging, everything is fine.
S. Todd Bartrim
Turbo 13B RV-9Endurance
C-FSTB
http://www3.telus.net/haywire/RV-9/C-FSTB.htm
"Whatever you vividly imagine, Ardently desire, Sincerely believe in,
Enthusiastically act upon, Must inevitably come to pass".
I don't see a Zener diode to clamp any spikes.
Finn
Haywire wrote:
Attached are a couple of pics of my tach divider.
It can be set to divide by any number necessary. I can't guarantee it
would work with any tach but it works very well with my cheap off-the-shelf-at-any-autoparts-store,
Hastings tach. I have a few more if anybody wants one.
S. Todd Bartrim
Turbo 13B RV-9Endurance
C-FSTB
http://www3.telus.net/haywire/RV-9/C-FSTB.htm
"Whatever you vividly imagine, Ardently desire, Sincerely believe
in, Enthusiastically act upon, Must inevitably come to pass".
The
EC-2 tach output has 12 pulses per revolution, and won't directly
work with any normal tach. Todd has made a divider to bring the pulse
rate down to normal, and it sounds like it's working well. The TT
that you have expects 1 pulse per rev, so if you don't mind dividing
the rpm reading by 12... :-)