DIY LED Tacho [Archive] - Kiwi Biker forums

Mattzxr750

3rd August 2008, 13:47

Okay i have some questions for all the electrical gooroo's out there. i found this curcuit on the web. And was think about building it.

102167

It looks simple to build i was just wanting to know.
1. Will it work? does the curcuit make sence?
2. can the voltage regulater LM317T (1-27v output) which is there to limit the voltage to 8 volts, can it be replaced with one that is is set to 8v, removing the 50k pot?
3. and in doing that will it effect the curcuit in any other way?

102166

I have started to build it, and it doesnt want to work. It may have been some thing I have done. I just want to rule that out

Any help would be great

dhunt

3rd August 2008, 14:03

Replacing the LM317,VR2 & the resistor labelled 510 with a LM7808 or similar 8V voltage regulator would not change how the rest of circuit behaves.

I'm not familiar with the two chips but nothing looks particularly wrong at a glance. What exactly does "it doesn't want to work" mean?

Do you have access to any test gear? Multimeter etc? The first step would be to check that you have 8v on all the approriate pins etc.

Give me a few more details and I might be able to give you some better advice.

Mattzxr750

3rd August 2008, 14:12

Okay, after building the curcuit and connecting it up, i notist that when the revs on the bike change the output from the LM317 changes.

When I connected the input wire upto the tacho on the bike no thing happened, no leds came on, there was a small amount of power at the leds.

As for test equipment i have a muiltimeter but thats about it

dhunt

3rd August 2008, 14:27

OK here's some questions/things to check?

1) What does the output voltage of the regulator fluctuate between?

2) I would suggest putting capacitors on the input/output of the regulator to help improve the voltage regulation. Say a 10uF electrolytic (This can only go one way round) on the output and a 100n ceramic on the input for a start.

3) With the bike off. You should be able to adjust VR2 to get a nice 8V output.

4) What are you using as the input to this circuit?

5) The first chip is a frequency to voltage converter. On pin 5 of the 2nd chip (output of the first chip) you should see the voltage fluctuate with rpm. If doesn't happen the problem is probably with the 1st chip.

This should hopefully give you a bit to get started on. Let me know how you get on.

Mattzxr750

3rd January 2009, 12:32

After having more time to find better better curcuits i came across this one. Im hoping that it will be better due to the fact that it has more info:

http://www.t-r-j.com/Auto/Tach/tachometer.htm

Going to start working on it this week. any one got any idea if it will work or not?

xwhatsit

3rd January 2009, 13:26

After having more time to find better better curcuits
I don't think there was anything wrong with the original circuit -- just guessing, but sounds like you cocked up the voltage regulator somehow (you said output voltage was rising and falling with RPM?) and fried the logic ICs. CMOS is pretty delicate, I always seem to cook them just by touching the pins accidentally :mad:

Your new circuit is even more complicated and has even more fragile ICs that need soldering (may I suggest using IC sockets?). I know diddly-squat about whether it will work or not but people generally don't upload non-working schematics with instructions onto websites to trick people.

Mattzxr750

3rd January 2009, 14:34

I don't think there was anything wrong with the original circuit -- just guessing, but sounds like you cocked up the voltage regulator somehow (you said output voltage was rising and falling with RPM?)
I think you are right about that.

Your new circuit is even more complicated and has even more fragile ICs that need soldering (may I suggest using IC sockets?).

and this time i will use IC socket so i can reuse the ICs over and over, every time i stuff it up

davereid

3rd January 2009, 15:41

Mattzxr750

3rd January 2009, 16:32

First circuit and second circuit are pretty similar, the second one has better protection for the frequecy/voltage converter, and adds extra LEDS with a second cascaded bar graph driver.

I quickly looked up the chip doing the freq to voltage conversion - I could only find an 8 pin device with that part number, not the 14 pin device in the sketch, so I guess they must be using a different variant.

Stick with the first one.

Looking around i found a way to swap the LM2907-8N(8 pin) for the LM2917(14 pin)
http://www.edaboard.com/ftopic186142.html

Ever where i look i find a different version all basicly the same, just with very small differences. I think i will stick with the 2nd one because its closer to what i want. so tomorrow I go and get the parts, and build.

But today i plan and plan and ......
plan

Thanks for the input so far, anymore would be a great help.

craisin

4th January 2009, 17:06

sounds good

hayd3n

4th January 2009, 17:31

would be swee it i had one of these would look so original

Mattzxr750

4th January 2009, 19:56

so far, have it half build...
tomorrow the other half

gixxer-king

7th January 2009, 15:29

wel that was an anti climax. did it work or not, i want photos:wari::soon:

Mattzxr750

7th January 2009, 16:37

its finished, how ever haven't tested it yet. will put more info and pics up tomorrow

motorbyclist

7th January 2009, 20:51

how much did all the bits cost?

and what, roughly, is the rev range covered? how adjustable is that?

Mattzxr750

8th January 2009, 16:28

wel that was an anti climax. did it work or not, i want photos:wari::soon:

So far no luck with getting it going it looks okay. But i think the schematic is wrong. Heres a cuple of pics for now.

115433115434

how much did all the bits cost?

All up about $40

and what, roughly, is the rev range covered? how adjustable is that?

it should cover most, it is adjusted by R3

Mattzxr750

8th January 2009, 16:47

V2 has FAILED:brick:...

however this brings me on to V3, a circuit of my own design. Using the manuals for the LM 2917 and LM3914 i have come up with one of my own to try and i think this one will work :)

imdying

8th January 2009, 16:51

Keep posting!

AllanB

8th January 2009, 17:03

Looks like a subway train map to me .......:wacko:

A nice wee project there - post pics when finished please.

motorbyclist

8th January 2009, 21:52

it should cover most, it is adjusted by R3

damn, i suppose i should get my electrical hat on and have a look at that then - will be good revision before uni starts again

then i can have a tacho on my pocketrocket :D

gixxer-king

9th January 2009, 10:37

perhaps posting up what is/not going and where you have tested the know it alls here could offer some input? many hands make light work but maybe many heads can make led work?

motorbyclist

10th January 2009, 22:59

now call me a noob, but dont both the lm2917 and lm3914 require a +15V supply, not 8V as per specified in the OP diagram?

craisin

15th January 2009, 07:38

this part-time know it all thinks it would be easier to mark maximum speed in gear on your speedo face:2thumbsup and save your money for your vices:headbang:

NordieBoy

15th January 2009, 08:30

this part-time know it all thinks it would be easier to mark maximum speed in gear on your speedo face:2thumbsup and save your money for your vices:headbang:

And if your vices are motorbikes and electronics?

motorbyclist

15th January 2009, 11:01

maybe he doesn't have a speedo or tacho?

is there any more info on the required signal? my pocket rocket has two wires - the HT lead and the kill switch, and i think the only way to get a signal may be to wrap a few turns around the HT lead:crazy:

NordieBoy

15th January 2009, 16:17

is there any more info on the required signal? my pocket rocket has two wires - the HT lead and the kill switch, and i think the only way to get a signal may be to wrap a few turns around the HT lead:crazy:

The trigger wire leading to the coil?

motorbyclist

15th January 2009, 21:20

there is no trigger wire

just an HT lead and kill switch... i could use the kill switch but i think it'd kill the motor, chip, or both... same for the HT lead :rolleyes:

it's one solid unit, which is a right pain in the ass cause you have to replace the whole thing if you lose spark - at a total cost of $8 for a new one:niceone:

that's 5% of the total value of the bike! several tanks of gas! a third of a slick tyre!

NordieBoy

16th January 2009, 07:19

My DR speedo said to either wrap 5-6 times around the HT lead or solder to the trigger wire.
I could never get a clean signal off the HT. Maybe something to do with the twinspark head.

craisin

16th January 2009, 08:05

Mattzxr750

19th January 2009, 10:18

work sucks! anyway back to the project

now call me a noob, but dont both the lm2917 and lm3914 require a +15V supply, not 8V as per specified in the OP diagram?
looking at the tech doc for the lm3914 the circuit that they lay out runs on 5v.

And if your vices are motorbikes and electronics?
thats me :yes:

maybe he doesn't have a speedo or tacho?

I dont like my tacho so its getting the boot (and maybe the hammer)