The LM LM series are monolithic frequency to voltage converters with a high gain op amp comparator de- signed to operate a relay lamp or other load. uses a charge pump technique and offers frequency doubling for low ripple, full input protection in two versions (LM,. LM) and its. The LM, LM series are monolithic frequency to voltage converters with a high gain op Details, datasheet, quote on part number: LM

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I’m hoping someone can take a moment to help me and possible restor my sanity!

I’m stuck with a pin LM – i’ve got an 8-pin on order now, but damn it, I want to get this to work. I’ve built this on a breadboard using a modified version of http: I have then used the datasheet as well as this schematic to convert to 14 pin And heres my breadboard layout: To help save hands, I hooked an LED up to the output signal.

I’m not game to hook it to my ‘duino nor can I be buggered going out to the bike yet I then have another supply, also grounded to the common ground, thats 14V.


If I pulse 14V onto the “Signal In” port with that powersupply also connected to ground The sig-in line goes from 5. I’ve played around with a few variations. Its driving me nuts Im guessing now totally that my ‘test powersupply’ is putting 70ma across the base of thewhich is saturating it.

I feel well past my depth trying to sort this out Can anyone offer some guidance? Datawheet LM’s datasheet is at http: Checkout my projects development blog SLiDA. How are you pulsing the 14V? That chip is made to detect RPM, most engines Idle rpm-ish, so you’re going to need a bunch of pulses or it’s going to measure 0.

Ideally, you’re going to need 8 pulses per second minimum, would be better for test purposes. Yeah – I figured that i needed a decent ‘frequency’ Now slightly more awake – Im thinking the grounding of the negative SigIN is ‘producing’ a voltage because it causes the various caps to discharge – not because it actually runs through the IC Once it stops raining here, I’ll drag it out and put it onto the bikes injector input at least and see if that makes it behave better I think the problem is my Internal Zener references.


I think you problem lies with the input circuitry of the LM Pin 11 and Pin 1 are the two inputs of a voltage comparator. You have fixed Pin 11 at about 0.

Problem with LM Tach Circuit – 14 Pin version

Therefore to get the chip to do anything you have to take pin 1 above and below this point. However you have no DC biasing on Pin 1 so it will just swing about with the AC coupled input and not do anything.

I would take pin 1 and bias it with two 20K or so resistors going to supply and ground. Then put a 10K resistor to the cathode of D3 and the other end of it to ground. Then you stand a chance of getting the input to switch.