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Led Tach With Shift Light

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After an extensive search of the internet I have put the pieces together for a tach circuit that will work on our DRZ’s. This is a project for the “Electronics Nerds” that we may have here on TT. Everyone else would be advised to just order up a Trail Tech Vapor if they really want a tach. I also need to point out that I am by no means an electronics expert. I repair office machines for a living and that’s where my limited knowledge of electronics comes from. This is not that difficult a project if you take your time and quadruple check your work when you layout and solder the components. I have to admit I was shocked this thing worked the first time. I have never built anything like this before.

This is the circuit we will build. (Lost the link to the original author)

I used 7 green 2 yellow and one red LED in my design. The original design was for an automotive engine not a thumper. This circuit is designed for a full scale reading at 8000 RPM’s. This can be adjusted with VR1.

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The key components are the LM 2917 that converts the signal going to the ignition coil into a voltage that the LM 3914 uses to light the 10 LEDs. You use VR1 to adjust the tach to the shift point you want to use. I adjusted my circuit using my “Butt Dyno”. When the last LED lights the whole bank flashes to indicate it’s time to shift. There is a good range of adjustment here for you guys that like to bounce off the rev limiter.

VR2 is used to set the voltage regulator (LM317T) to 8 volts. I would assume it would be ok to just use a fixed 8 volt regulator here. I had a LM317T and a 25 turn 10K pot in my junk box so I just used what was called for in the original design. The circuit is “tuned” for 8 volts so this step is critical.

Here are the links to the data sheets on the LM2917 and LM3914 if you want to learn more.

http://www.national.com/ds/LM/LM2907.pdf

http://www.national.com/ds/LM/LM3914.pdf

To save yourself some hassle if this thing does not work, test the assembly before mounting it to the bike.

Connect your power and signal wires to some alligator clips. Remove the seat and CDI connector cover. Push a straight pin into the white wire going to the coil (large connector on CDI. Not the four pin connector.) Connect the signal wire to the pin and the power leads to the battery. Adjust VR2 for an output of 8 volts. Now fire the bike up and with any luck you should see the first LED light up. Try turning VR1 in either direction to see if it comes to life.

All the component values are listed on the diagram. I would suggest getting LED’s with at least 300 mcd (brightness) so they are visible in sunlight.

I purchased my electronics from www.digikey.com but feel free to source them from your favorite vendor. I found the project box at Radio Shack and the flat cable connecting the LED’s was cannibalized from a computer game port.

The project box I used had a circuit board that measures about 3x2 inches. It was almost too small to fit all the components on. There is room under the number plate for a larger box and board. Get one as large as you can fit in there so you’ll have more room to layout the components and make soldering it all together easier.

Total cost of this project for me was about $25.00 as I had most of the components on hand already. Here’s a partial parts list from Digikey which shows the LEDs are the most expensive item on the list. You have to buy 10 to get a price break.

1 1 1 0 0 LM3914N-1-ND 2.87000 $2.87

2 1 1 0 0 LM2917N-ND 2.11000 $2.11

3 1 1 0 0 LM317TNS-ND 1.79000 $1.79

4 1 1 0 0 490-2889-ND 0.85000 $0.85

5 10 10 0 0 516-1354-ND 0.34800 $3.48

6 10 10 0 0 516-1352-ND 0.34800 $3.48

7 10 10 0 0 516-1349-ND 0.34800 $3.48

8 2 2 0 0 1N4148WTDICT-ND 0.38000 $0.76

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I originally wanted to mount the LED’s in some type of rubber weather stripping and glue them to the backside of the number plate just in front of the instrument cluster.

But as usual I had to make it complicated and came up with the metal housing you see in the pictures. I filled the housing with epoxy to make it water tight and avoid vibration damage to the solder joints. To avoid vibration damage to the solder joints on the circuit board use a hot glue gun on the larger components to lock them in place.

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Tie wrap the circuit board to the wiring bundle so nothing touches any metal. Go for an “adjustment ride” armed with a small jewelers screwdriver to adjust VR1. Adjust VR1 until the unit flashes at whatever RPM you feel comfortable with. If you have a “real tach” then you could adjust the display to correspond to actual RPM’s if you wanted. Keep a sharp eye out for the local law enforcement as your tearing around bouncing off the rev limiter adjusting your new toy!

The project box just sits on top of the headlight with some foam padding added to snug it in place when the number plate is reinstalled. I tapped the power lead onto an orange wire that powers up with the ignition switch and tapped into one of the ground wires in the bundle. Connect the signal wire to the white wire at the ignition coil. Carefully tie wrap the wire to the bundle going around the steering stem so it does not rub.

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If anyone decides to build one of these please post up your version of this design.

Good luck

Dan

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While I give you props for taking the time to design and build all that....why do you need a tach on a four stroke single with a rev limiter that is known to be bombproof ? Again not baggin on you, but I look where I'm going.....not at a tach.

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While I give you props for taking the time to design and build all that....why do you need a tach on a four stroke single with a rev limiter that is known to be bombproof ? Again not baggin on you, but I look where I'm going.....not at a tach.

But you have to admit, it does look pretty cool

Good job! :eek:

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While I give you props for taking the time to design and build all that....why do you need a tach on a four stroke single with a rev limiter that is known to be bombproof ? .

Because he can and because it is pretty cool!!!:eek:

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thats great man, another member and I talked about this awhile back.

http://www.thumpertalk.com/forum/showthread.php?t=624731&page=2&highlight=shift+light

and the one you built was exactly my suggestion to him. Im glad it actually worked:). From that circuit you can probably drive an lcd if you wanted the actual number at some point.

Good Job!!

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thats great man, another member and I talked about this awhile back.

http://www.thumpertalk.com/forum/showthread.php?t=624731&page=2&highlight=shift+light

and the one you built was exactly my suggestion to him. Im glad it actually worked:). From that circuit you can probably drive an lcd if you wanted the actual number at some point.

Good Job!!

LOL..........that's the thread I saw that got me interested into building one:p

Thanks for the comments everyone.:eek:

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good night, someone can tell me if this scheme works for a karting 2

times?

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Hey! If you wanna be extra-fancy you can do the non-intrusive inductive pickup to get a frequency off the HT wire instead of direct-connecting to the coil. This circuit converts the dirty ignition current pulses to clean square wave. You could just put an RC filter on the output to make the square wave into a voltage. The duty cycle is adjusted with the potentiometer, but you can play with resistance values (of the associated resistor and the pot) to get the voltage output you need for the 3914 Dano is using to drive the bar graph.

inductivepickupcircuit.jpg

You just need to wrap a wire around the HT lead like so.... Only one end connects to the circuit.

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I made a fancy project box for a different purpose, but the point is that this portion of the circuit can be made fairly compact.

IMG_2290.jpg

This was all part of big juicy instrumentation project for an on-board "dyno" and data acquisition system, which works almost flawlessly...

IMG_2328.jpg

In response to "my version of the design" that thingy you see on my computer is a real-time LabVIEW tacho. :-P

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I managed to find this circuit, he used a 555 timer to create a light shift. I added the above circuit to get the signal. if I use this circuit, it will work? I have difficulty speaking English. I really needed some help.

possivel2.jpg

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Oh great, my inner geek just peaked. :thumbsup: I actually have all the components to make it..now to see if I can figure out the best way to assemble them. :confused: Thanks guys, I needed another project!

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NICE! But I'm way to lazy nowadays... Bought a tach with a shift light from KOSO.

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I managed to find this circuit, he used a 555 timer to create a light shift. I added the above circuit to get the signal. if I use this circuit, it will work? I have difficulty speaking English. I really needed some help.

possivel2.jpg

Can someone tell me if the circuit I found is correct?

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My theory on the horn is as follows:

Nobody ever notices me, ever. I lost count of the sidewalks I've been on as a result of a merge-onto-me situation. I have not enough fingers to count the times someone has made direct eye contact with me and pulled out in front of me. My only line of defense besides being a fairly good rider is to posses a device that is so strange that the idiots will at least have to ask "what made that noise?" That pause in their mushy brains gives me that 1/4 second I need to evade death by soccer mom.

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am looking for something like this. all thou I have an old 2stroke dt125a, sorry guys :( lol... but the old tach is gone along with oil pump. don't like things that use HP, if they don't make it go faster ! do like the bar graph, its easier to see when you hit the red line or its time to shift. although would like something more compact, think could come up with something. if had good schematic, the bike is fully LED headlights and all.  ( can I get some help with this? )

Edited by madmatts

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am looking for something like this. all thou I have an old 2stroke dt125a, sorry guys :( lol... but the old tach is gone along with oil pump. don't like things that use HP, if they don't make it go faster ! do like the bar graph, its easier to see when you hit the red line or its time to shift. although would like something more compact, think could come up with something. if had good schematic, the bike is fully LED headlights and all.  ( can I get some help with this? )

Pics of the DT or it didn't happen.

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Pics of the DT or it didn't happen.

pic's tried to attach to post, but asked for url. their not on a web page, just on pc. will see if can add some to profile, but it's true it's all LED. the thing is not to control voltage at the light, but at the source. with that, the hole wiring harness on the bike is cat5 cable. except for charging and ignition circuit, which are key switch- battery. oh the batt is one used in exit signs, in a regular office building. half the size, ya wont crank it. unless its hot, and you catch it on the first compression stroke. after that just don't have the amps. will try post some pic's

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1974 dt125a electric start, bought it in a garage sale in 2003 for 150$. was a bag of crape, got it running. took out in trails, it sucked large........ top end'd it, what a dog, might have been that my last dirtbike was canam400. anyways it ended up in the corner for ten years, till other winter had nothing to do. so this is what I came up with.

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Edited by madmatts
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