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Really cool tachometer...fast too!

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Home-made tachometer.

Fast....instant reading. No waiting for refresh like the after-market ones.

Cool-factor is off the scale IMO.🤣

Unique. Never seen anything like it on a bike.

Bright. Uses ultra-bright LEDs.

Accurate. All chips used are the linear versions, and circuit is voltage-regulated.

LED Meter in background is frequency in Khz.....multiply by 60 to translate to equilvilent RMP reading.

Draws about 1 amp at full red-line. About 1/4 amp at idle.

Cascaded 3 LM3914 LED bar drivers for 30 total LEDs.

Used LM2907 frequency to voltage converter to drive LM3914 LEDs.

All components bought off EBAY for total cost of about $10.:applause:

Plan on spending at least 10 hours to build though. :banghead:

I'll be mounting it up on the bike next week.

Idle

http://members.bellatlantic.net/~vze3sdb7/P9280022.JPG

Mid-RPM

http://members.bellatlantic.net/~vze3sdb7/P9280020.JPG

High-red-line

http://members.bellatlantic.net/~vze3sdb7/P9280019.JPG

Movie of meter in action

http://members.bellatlantic.net/~vze3sdb7/P9280025.MOV

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Isn't there something easier...like multiply by 10 or 100 or something...60 might get kinda hard to do while riding... :banghead:

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60 is tough to work around....good thing that I'm only using the digital meter on the bench to calibrate the circular homebuilt job:D

Pullin'

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GREAT START!!

Why the high current draw? You could reduce it by running the 3914's as single dot drivers.

What signal will you be using on the bike for the frequency source and how will you condition it?

The LM 3914 is a great little chip.

Ride on

Brewster

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RE LM2907....I did.🤣 See 1st post. I tried a one-shot 555 setup, but my attempt lacked the linear/stability properties that was required to do this properly. :banghead:

RE: 1 amp: 20Ma per LED times 30 plus red-line flasher comes in at just under one amp. Single dot would bring that way down, but I liked the bar. Also, the dot mode does not work to well for anything above 50mv per led when cascading.:applause: I'm thinking about dropping the LED current down to 10Ma....at least for the blue LEDs.

RE Signal source: Straight off the CD coil primary. The bike already had a connection to the coil in the wiring harness that leads all the way up to the headlight (probably for a tach option used by other bikes that use the same harness).

Pullin'

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You can use a decade decoder or a 7-segment display counter/driver to divide by six.

Now the frequency should be relative to a voltage that is base 10 from the RPM, or mutiply by 100.

Or put series dropping resisters to the bar display drivers to calibrate them.

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.02 x 30 = .6

.03 x 30 = .9

since the range of led current is programmable out to 30 milliamps, you may want to double check your current programming. I missed the 2907 mention in your first post.

I have actually been toying with this concept to drive a zero centered bar display for enduros. That way if your avg speed is on time the display is off and lights to the left (too slow) or the right (too fast) based on how far off you are.

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700IACS,

The tach is currently calibrated for full-scale deflection (all 30 lights lit) at 10,000 RPM. It is a linear. At 1,000 RPM only 3 lights light up.

The "multiply by 60 comment" was only relative to the digital counter in which I used to calibrate it with. It reads out in Khz. It is irrelevent, in that the digital counter will not be installed on the bike.:banghead:

Pullin'

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700IACS,

The tach is currently calibrated for full-scale deflection (all 30 lights lit) at 10,000 RPM. It is a linear. At 1,000 RPM only 3 lights light up.

The "multiply by 60 comment" was only relative to the digital counter in which I used to calibrate it with. It reads out in Khz. It is irrelevent, in that the digital counter will not be installed on the bike.:banghead:

Pullin'

10-4

Good work!!!

Maxim and other companies make a number of LED chrage-pump type current regulator ICs if you wish to reduce the load. You might be able to do the same with a TLV431 voltage reference set up as a current regulator. Otherwise, simple resisters will also do the trick.

A zener diode with each LED might help reduce the "leakage" and help with a sharper transition to the next LED. Either way, it looks cool. Now I want to make one.

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RE Signal source: Straight off the CD coil primary. The bike already had a connection to the coil in the wiring harness that leads all the way up to the headlight (probably for a tach option used by other bikes that use the same harness).

Pullin'

I guess that you've looked at that signal with a scope? If so, can you give some details as to the voltage, shape, and duration of that signal. I've been toying with an EFI unit for bikes and that informaiton would be great.

Thanks

Brewster

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Where do you plug in the flux capacitor?

You electronics guys are nuts! In a very cool sort of way. :banghead:

Cool project. Now, who will mass produce it for the rest of us motorheads?

Dan.

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Or you could buy a "tiny tac" for 30+ bucks and be done with it. and draw no power.

Check them out I run one on mine with great succsess

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Or you could buy a "tiny tac" for 30+ bucks and be done with it. and draw no power.

Check them out I run one on mine with great succsess

Nice unit for the price, includes hour meter. www.tinytach.com

BUT, the display update is slow, every two seconds.

Ride on

Brewster

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Nice unit for the price, includes hour meter. www.tinytac.com

BUT, the display update is slow, every two seconds.

Ride on

Brewster

You have to order the "commercial" version for a faster refresh speed.

Even so, such a unit is useless IMO for high dRPM/dt situations under acceleration. It is designed for static RPM measurements. Your brain also processes graphical indicators much faster than numbers. This is why analog needle gauages have never, and probably will never, go away.

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You have to order the "commercial" version for a faster refresh speed.

Half second display update for about twice the price.

Ride on

Brewster

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700ACIS,

ditto on the analog sweep display.....instant read with zero thought. There is a nice 3rd party needle-sweep model that can be had for about $90? When I was looking I considered it. I never even gave the digital LCD ones a second thought.

PS: Most of the newer OEM needle tachs that come on bikes are electronic. I wonder if they can be used with any bike? They can be had cheap on Ebay cheap.

Pullin'

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