tachometer using 555 IC and LM3917

Can you exercise the input with a square wave generator?

Which manufacture ???

The TLC555 is a low power CMOS, is the 555 you used a NMOS ??

Do you have a o'scope available ??

Did you wire this up yourself ??

Did you wire up more then one unit yourself ??

Desperate enough to pay money ??

Help us help you, give enough information, please.

PS: learn how to spell.

the 55 IC iam using is NE555N.do i need exactly TLC555 or 7555 IC?

no i don't have osci'scope.but i tried blow ckt.and the LED present in the ckt start flashing when i rise the throttle of motorcycle.

i don't understand where and what iam doing wong.is the elektor tachometer ckt right?? or its not working bcz of using NE555N insted of TLC555???

You have no idea what you are doing.

There is more than building a circuit then replace parts without reviewing the data sheets.

If you used all the parts suggested in the parts list and it still did not work, would you blame the author for writing the project wrong.

Good Luck.

In message , dated Mon, 21 Aug 2006, Donald writes

Depends. Some magazines employed illiterate hippos as printers, so you could never trust the circuits and parts lists to be error-free. Some still do; you see '47MW' resistors and '1000 F' capacitors called up.

well iam not blaming any one.i just want to confirm. some guy just mailed me abt this elektor tachometer,that they printed wrong resistor values.and they corrected it in the next release. and iam from mechanical filed.i don't have much knowledge in electronics(just moderate).problem is i have to finish this project all by myself. so iam asking u ppl as u know more than me. any more views regading this project will be appriciated. thanks

No- you *must* use a CMOS 555 like the TLC555 for two reasons: C3,R3, and R4 are sized for a CMOS input current and 100ms time constant, and it is essential that the 555 output go all the way to 5V. The bipolar NE555 types will not work in this circuit.

Sure-that's fine.

Use a TLC555 and see if that doesn't improve things.

Measure the voltage on C1 with a digital voltmeter. If you have increasing voltage there with RPM, did you put that jumper in???

Luhan

thanks fred(and other ppl too) i'll try cmos version of 555 first(can i use 7555 insted of TLC555 as it is also cmos version).and will post results.

iam using breadboard for trials. i'll try 555 circuit first and then combined with LM3917.

No, or probably no

With it outputing 5 volts - the thing is probably not working because the timing values are for a cmos 555 not a bipolar - recalculate or switch parts first.

Beyond that. . . I had the same problem and ended up using a toroid - pass the cable through the core and wind a few turns around it for signal ground one end use the other to input the 555.

You should be able to test your circuit by repetitively grounding pin

I wasn't too happy with the toriod on the spark plug because it took so much filtering to have only one led light at a time, that I was looking at the RPM ten seconds ago - I ended up using the signal from my 12 pole alternator with just a little filtering. One pulse per revolution isn't enough for a fast reaponse.

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u mean like this.ofcourse with lesser dia. core. (sorry for such bad pic)

first i want to trial on sparkplug cable only.if it failed i'll go for other method.as currently i don't have tools to messup with my motorcycle. and someone told me not to connect other end of signal wire to ground.i think i need to experement these 2(imean connecting to ground and leaving the end)

Yeah, just like that. Or one of the "clam shell" type cores radio shack sells to put around power cords to limit RFI might work

Wrapping the sense wire around the spark plug wire does not provide an "inductive" pickup. The wire is not oriented correctly to inductively couple much energy. Leaving it ungrounded gives you a capacitive pick up.

When you use a core you're making a transformer with a single turn primary (the spark plug wire) and need to ground one end of the secondary to develop voltage input to your circuit.

I started with the 555 charge pump then tried a LM2917 (I think that's the number - frequency to voltage convertor) Better smoothing with a smaller cap, but still not what I wanted. Leds have the ability to outperform a mechanical meter for response time - seemed a shame to hobble them with a large filter cap.

Use whatever you want - the current and voltage are low it won't matter too much. Better to wind the wire around the entire core rather than have all the turns bunched at one side - so space them out.

When I started thinking about what I was doing . . . do I really need to know when it is turning 500 RPM? My motorcycle idle speed is supposed to be 1100 RPM and it won't run slower than 800 RPM, so one LED is virtually useless unless the starter motor is spinning the engine.

Then the idea of only 20 LEDs wasn't too my liking either. Red-line is 12,000 RPM not plus or minus 500 RPM. The final version of my tach used a set of four comparators to change the scale of the 20 led display. 1000-4000, 4000-7000, 7000-10000, 10000-13000.

Each of the comparators has a reference voltage that they compare to the signal from the charge pump, as each comparator's range is exceeded it lights an LED to tell me the range it is on, and connects its reference voltage to the display (via an analog switch IC).

So I've got 20 LEDS doing the work of 80 and have 150 rpm resolution - and it took me a month to get working. but the display goes around four times now.

I used a 4" PVC plumbing fitting for a housing and put a thin ring of

Most of the time and fun was on the breadboarding of it and developing the idea. I think I have something like a total of 7 IC's in it if I count the two regulators (one is for the power supply and another for the reference).

I even incorporated a high/low switch for display brightness but found that 6 ma per led was more than enough for high efficiency leds.

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sure i'll keep in mind abt grounding the other end of pickup coil.

wow thats a quite detail explanation. thanks a lot. at first i want to use that F-V converter only(LM2917) and i found circuit in this german page.

Well I'm an American don't speak much but English and a smattering of Spanish - enough to get me in trouble most days.

The LED digital tach in the German picture - is there a link to the schematic? Sorry for my ignorance.

I have an absolutely - "damn wish I'd thought of it" schematic of a 64 LED display from a guy that makes use of a 8 bit A/D converter and decodes the display into a 8X9 matrix using a few common CMOS parts. That is 64 LED's with only three IC's ... minus the regulator, and only 20 wires to the display board.

At the time I built mine. the LED's were costing 29 cents each and using 20 to represent 80 was a cost consideration

I built my tach four years ago and it has been on the MC ever since. I have a shematic that I put in my notebook and can scan and send and it will give you an idea of what I did.

Should I send it to snipped-for-privacy@gmail.com ?

Take care bob

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I was looking at your web space - what does the alternator file contain? I just rewound the rotor coil on my bike and wondered if there was something I might use.

I'd rather replace the field coil with permanent magnets and then just design a new regulator.

The program for the USR modem? what does it do?. I have a USR external.

Thains bob

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yes in download section u'll find the circuit details.if ur facing problem with the langauge then use altavista's-bable fish translator to read the site.this site contain 40,30,20 LED tachometer circuits with PCB layout.

if possible do mail me the schematic of your tachometer.u said it uses LM2917 is it 8-pin or 14-pin. thanks

Right- the author of the Elektor article mentions "induction" and the "high voltage" in the spark plug cable. He doesn't translate into English very well because his sensor is capacitive and works on the principle of rapid voltage collapse in the wire when the spark fires. The 20 wraps of the sensing wire around the spark plug wire form a small capacitance, and the rapid high voltage collapse in that wire couples charge into the sensing wire and into the 555 circuit, triggering it. There is no connection to GND. The sensor is just a single wire going from the 555 circuit to the plug cable, wrapped about 20 times, and ends there. This is better than an inductive type pickup using a core in some ways because it is immune to stray magnetic fields. You seem to be having a problem following directions. Elektor doesn't publish circuits that have not been built and tested, which means it will work as advertized if you follow the directions. But when you go off on your own changing part numbers, component values, and sensing methods, when you don't know what you're doing, you will end up with a pile of malfunctioning crap.

could be. because the article is quite old.and its kinda hard to get the exact components in the market.still iam trying my best to get them.(7555 insted of TLC555 as both r cmos versions) and till now i experemented the signal wire by leaving the other end,and was using less dia wire.this time i'll try different dia wires with 7555 IC.

Done

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