lww

But once you've re-calibrated the speedometer "gears" to measure mph when the speedo is configured to display kph while the odometer is ALYWAYS configured for mph and takes it's signal from the speed sensor which takes it's signal from the speedo "gears" will begin to accrue miles at a rate 37.87% slower than it should.

terrymac

4/15/09


The diode id not fix the speedometer jitter,
mph goes/down 3-5 mph, lookng like ts hunting for
correct speed.

I believe that after rebuilding the clock using larger
24 gage wire for ground & connections to discrete
analog components (caps/resistors) that set the timing
for the NE555 was the problem.

Buiding this speedometer required using 30 gauge
wire for wire-wraping the component connections.
However, had I used 26-gauge wire there would be
no issues with ringing/jitter of clock timing and speed
ranging up/down 3-to-5 mph (depends on how much
jitter/ringing.

You definitily need an oscilloscope to troubleshoot your
speedo circuitry. I made some signal measurements,
The signal at Pin-3 of the Ne555 is a pulse 75-80 miro-
seconds wide, and the period varied by R6/R8 for MPH,
and R7 for KMPH, was 16-18 millasecond.

The Counter U4, has 3-signals used to gate-in , by the MR,
the speed pulses from the speedo 26-slot speed signal
(pin-12), master reset (pin-13), and the Latch Enable
(Pin-10). And Display on (Pin-11) to clock-out the Speed
Value from U5.

The U5 signals, LE was 20 ms On/and 140ms Off, while the
DIS was 38-40ms On/and 120ms Off, the MR from U4 is
connected to a RC and diode. The RC causes the MR signal
to Spike Spike-On and then discharge (ramp-down) to about
1vdc then drop to Off. The Spike On and Discharge time is
20ms, and the Off time about 160ms. This where bad wiring
can cause jitter/ringing.

Well thats about All the info you may need to get through
building your Digital Speedo for your Digital Dash.

I happened to go through a radar speed display today and
All readings were the same: my dash, my external speedo and
the radar showed 31MPH.

Please drive/speed safely and enjoy the new speedometer
which will show your Zs TOP-END beyond 85-MPH.

Terry Mathieu





Sorry guys.. if you tried to build my Digital Speedo
from my Schematic... it has a few Errors,
as of 4/13009 at 40mph has 3-mph jitter.
The Diode noted below should resolve the
jitter.

So look at the Schmetic and do the following.

Delete ... 1) C5 from the Oscilliator ,
there should only be C3 conected to
Pins 2 and 6.
2) R8b from the KMPH ,
the single 100K pot will do the calibration

Changed Value... 1) the Differential resistors
R3-R4 are 100K and R1-R2
are 47K and the Red/Green
wire connections must be
connected to the Internal
Digital Speedometers Red/
and Green wires. I found it
better to solder the connections
and use heat shrink tubing to
insolate the conections from
beeing grounded.

And for the Jitter, ADD ... Diode across R10 with the
Bar towards the Capacitor.

I will know tomorrows driving test, if the Diode
resolves the Oscillator jitter and Speed should be
stable ( I hope) no ringing/jitter. My borrowed scope
showed No Jitter.


Observation... you shoukd see a20 micro second pulse
from Pin-3 of the NE555 timer Clock which drives
the 4017 Counter whic produces the Speedometer MR
master reset pn13, LE-Latch Enable , andDIS- Display
signal timing.
From the Differential input signals pulses from Pin-4
of the 74LS14, this is the Speed input to counter. You
remember that whell which has 26 slots in it (that the
actual rate the wheel is turning Which is Speed.
So you calibrate the clock Ne555 timing so that the 4017
readout is correct. Since I have a working Digital Dash
I bought from ebay, I used a high speed drill as the speedo cable input.

You don't have to have both US and International MPH
or KMPH. if you want kmph just leave R8b and R7; if you
only want MPH, leave out R8b and R7.


If you want the math on digital speedometers do an
internet search on Digta Speedometer and Narendra
Wadhwani has a detail math and distance calc.

I have decided Not to manufacture the digital dash as I
do not want a 2nd career.

JEZ280ZX

Hi,
My old Japanese spec Z32 had a 180kph speedo fitted which was converted to read 180mph by attaching a device to the wiring at the back of the dash....So I'm sure something similar is available for motorbikes or cars with digital readouts too.
Cheerz,
Jez.