u mean like this.ofcourse with lesser dia. core. (sorry for such bad
pic)
http://img221.imageshack.us/img221/8909/ideaof4.gif
Yeah, just like that. Or one of the "clam shell" type cores radio
shack sells to put around power cords to limit RFI might work
first i want to trial on sparkplug cable only.if it failed i'll go for
other method.as currently i don't have tools to messup with my
motorcycle.
and someone told me not to connect other end of signal wire to ground.i
think i need to experement these 2(imean connecting to ground and
leaving the end)
Wrapping the sense wire around the spark plug wire does not provide an
"inductive" pickup. The wire is not oriented correctly to inductively
couple much energy. Leaving it ungrounded gives you a capacitive pick
up.
When you use a core you're making a transformer with a single turn
primary (the spark plug wire) and need to ground one end of the
secondary to develop voltage input to your circuit.
**have u used 555 ic for ur tachometer?
I started with the 555 charge pump then tried a LM2917 (I think that's
the number - frequency to voltage convertor) Better smoothing with a
smaller cap, but still not what I wanted. Leds have the ability to
outperform a mechanical meter for response time - seemed a shame to
hobble them with a large filter cap.
what shld be rough dia of wire that shld be wound on ferrite core?
Use whatever you want - the current and voltage are low it won't
matter too much. Better to wind the wire around the entire core
rather than have all the turns bunched at one side - so space them
out.
When I started thinking about what I was doing . . . do I really need
to know when it is turning 500 RPM? My motorcycle idle speed is
supposed to be 1100 RPM and it won't run slower than 800 RPM, so one
LED is virtually useless unless the starter motor is spinning the
engine.
Then the idea of only 20 LEDs wasn't too my liking either. Red-line
is 12,000 RPM not plus or minus 500 RPM. The final version of my tach
used a set of four comparators to change the scale of the 20 led
display. 1000-4000, 4000-7000, 7000-10000, 10000-13000.
Each of the comparators has a reference voltage that they compare to
the signal from the charge pump, as each comparator's range is
exceeded it lights an LED to tell me the range it is on, and connects
its reference voltage to the display (via an analog switch IC).
So I've got 20 LEDS doing the work of 80 and have 150 rpm resolution -
and it took me a month to get working. but the display goes around
four times now.
I used a 4" PVC plumbing fitting for a housing and put a thin ring of
4" pipe in it to give me a ledge to seal the display board to - I
didn't use a PC board and made it in two assemblies.
Most of the time and fun was on the breadboarding of it and developing
the idea. I think I have something like a total of 7 IC's in it if I
count the two regulators (one is for the power supply and another for
the reference).
I even incorporated a high/low switch for display brightness but found
that 6 ma per led was more than enough for high efficiency leds.
