I have found a few schematics that show how to use a 555 timer as a simple tachometer. They all state that the income are pulses that are collected at the low side of the ignition, the breaker points. My bike has an electronic ignition, if I used one of these 555 based tachs on my bike will it cause any harm to the ignition? The bike, a Harley Sportster, already has the wiring for a tach. routed from the ignition, but no tach. (I do believe).

 

Well Paddy boy, looks like you'll have to go elsewhere for an answer to this highly technical question. Nobody here can anwer it.

 

I've posted this question in general electronic chat, but received no reply. Perhaps I should introduce myself first.

My name is Patrick, I'm an older retired fellow, I retired two years ago, I drive a Harley Sportster and will continue to do so until my legs will no longer straddle the bike. I do a lot of my own work on the bike. I also have experience and education in electical technology, and am still quite interested in the science. I came across this forum while looking thru the internet for information on electronic tachometers.

I want to build a tach. for my harley sportster. I have schematics and information required to build. The diagrams that I found state that the input comes from the ignition points. I'm concerned that since the bike has an electronic ignition, will a homemade tach. cause damage to the ignition?
Thank you
Patrick

 

If anyone else has a better reply please chime in.

Educated Guess: I doubt that you will hurt the ignition system itself. There is a very small chance that you could fry the bit that provides the tach output itself.

The tach output may work as is. You need to determine what voltage the pulses are, either from documentation or by hooking a scope to it.

Once you know the voltage you can condition the signal to work with a tach circuit if needed.

I hope that helps.

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hi Patrick,
You say you have a 555 timer/counter circuit, can you post it?

Also I expect you have a diagram for Harley's ignition/tacho connection?

Can you post that part??

I suspect that you are not getting a lot of replies, is because of lack of information.

If we sort it, whats the chance of me getting a road test ?? [pillion of course]

Regards

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Hopefully you've learned a valid lesson about this forum.

Please don't make duplicate posts, they're very annoying and don't help you or us to help you. Creating duplicate threads does not increase your chance of a useful response, it only reduces it as people get confused and can't always see what others have suggest in the other thread.

It can take a couple of days for someone to reply to a thread and you only waited a few hours. Please try to be more patient, if you don't recieve a reply within a week then try bumping the orignional thread and adding more information.

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ericgibbs:
Thank you for the polite reply.
Here is an image from the net. TACHOMETER CKT USING 555 TIMER
I hope it makes it thru. I have others but they are quite similar. I scanned them onto my printer/scanner, but I don't quite know how to transfer them to this forum. I won't try, because I don't want to get into any more trouble with the powers that be.
Once again, thanks for the polite reply. After reading some of the posts by the "old timers", it appears that there are quite a few that are not very receptive to new comers, especially those of us that ask stupid and/or boring old questions that probably have been asked before. And very especially to dumb newcomers, like myself, that followed improper procedure. But that's typical of specialty forums.

 

Hero999 said:
Hopefully you've learned a valid lesson about this forum

OH, have I ever.

 

Electronic motorcycle ignitions are contained in a sealed package. If one part inside burns out, then the whole thing must be replaced at a cost of $140. or more, that's a cheapie.

Quote:

Sturgis comes but once a year.

 

I would guess that the reason you've gotten so few replies is because not many here are experienced with motor cycle ignitions. Neither am I, but the first thing to check is if the primary of the ignition coil is switched low side (As in your 555 tacho diagram) or high side (One side of the coil grounded). If it is the same as in your diagram then it should work fine. R1, the 1k resistor, should limit the current to a safe level so nothing should be harmed by adding this circuit to your bike. Just be careful when you wire it as you already know what a mistake will cost you.

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hi patrick,

As kchriste points out, there is nothing in the circuit that could harm the ignition system.
Just ensure that all is connected correctly before starting the bike, I am assuming the Harley has a 'negative' ground???

Lets know how it goes, a future OP may ask the same question.

Regards.

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Thanks to 3VO, KCHRISTE and ERICGIBBS
Here's something I found that might work as a tachometer for me. I'll have to order the part.

LM2917 - Frequency to Voltage Converter

• Ground referenced tachometer input interfaces directly with variable reluctance magnetic pickups
• Op amp/comparator has floating transistor output
• 50 mA sink or source to operate relays, solenoids, meters, or LEDs
• Frequency doubling for low ripple
• Tachometer has built-in hysteresis with either differential input or ground referenced input
• Built-in zener on LM2917
• ±0.3% linearity typical
• Ground referenced tachometer is fully protected from damage due to swings above VCC and below ground

I don't know why the image didn't present itself, but
more info. on this site: http://www.national.com/pf/LM/LM2917.html

 

Man, I hope it works this time
LM2917 - Frequency to Voltage Converter
lm2917tach2.GIF
I think you can click on for larger image
• Ground referenced tachometer input interfaces directly with variable reluctance magnetic pickups
• Op amp/comparator has floating transistor output
• 50 mA sink or source to operate relays, solenoids, meters, or LEDs
• Frequency doubling for low ripple
• Tachometer has built-in hysteresis with either differential input or ground referenced input
• Built-in zener on LM2917
• ±0.3% linearity typical
• Ground referenced tachometer is fully protected from damage due to swings above VCC and below ground

 

Harley Sport. has negative gnd, but has only two cylinders
gasoline tachometer

gastach.JPG

click on image for larger view

 

hi patrick,

The timing components for LM2917 circuits, seem be selected for a 4/6/8 cylinder otto cycle.
It should be possible to modify the pin# 3 components to give an output to suit a 2 cylinder engine.

I would prefer the circuit that has the adjustable calibrate control.

Does this help?

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