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Hi
Finn;
You got me thinking that I could come up with a better
solution, than a voltage divider. I built the circuit on a breadboard again, but
using a capacitor across VDD & VSS this time. I tried various capacitors and
was unable to improve on the stability at higher voltages without a voltage
divider. I was considering ordering a couple of regulators (still the best idea)
when I started considering that I really don't know anything about the output
pulse from the EC2 other than it is a 12pulse/rev signal. So I borrowed a Fluke
scope from our shop and brought it to the airport to have a look at the wave. It
is a square wave 768mV peak to peak, base voltage 8mV (I guess I could have just
asked Tracy :-). This surprised me as I was expecting 5V. In experiments on the
breadboard I found that the counter performed well at voltages up to 20V as long
as the clock input was not greater than 5 volts below supply voltage.
Now it's becoming a little more clear (remember, I'm just an apprentice). When I
showed the waveform to a journeyman at work, he also was so surprised, he
suspects it's not correct. Tracy can you confirm this P/P
voltage?
The voltage divider, while being a little crude, is
effective, so I may just stick with that, unless I can find a couple of 5V
regulators in the spare parts. Since I expect that once the EM2 becomes
available, most builders will chose to use that since it really is a great tool,
so there won't be any reason to get too carried away with this thing. Besides
I'm just giving the darned things away because I had 24 extra counter chips, so
I shouldn't start buying parts -- no wonder I can never save any money
:-)
John
and Dave;
I'll try to get a couple sent off before next week.
John, I'll need an address.
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".
A capacitor accross the supply pins should
be fine there. I was thinking about the input. Of course if your input comes
from Tracy's controller, that's probably not an issue. But from anywhere else,
like coil pick up, some input filtering/clamping would be
wise.
Finn
Haywire wrote:
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... :-)
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