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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Therefore to get the chip to do anything you have to take pin 1 above and below this point. I understand that, the input opamp works as a comparator and converts the sinusoidal signal into digital pulses. It is drawn to be a comparator rather than a buffer. Sign up using Facebook. The data sheet provides the detailed arithmetic, but the telling point is that the relationship between input frequency and output voltage only depends on C40 and R All the capacitors and resistors are connected to ground; I’m very confused at this step.

An example circuit from the datasheet. R46 is acting as a load for the charged signal.

Page lm917 of the data sheet says it all. 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 What is the function of the second opamp?


However you have no DC biasing on Pin 1 so it will just swing about with the AC coupled input and not do anything. Andy aka k 10 Read towards the bottom of page 8 on the data sheet.

RBerteig 6 You have fixed Pin 11 at about 0. I’ve built this ddatasheet a breadboard using a modified version of http: Can anyone offer some guidance? Im guessing now totally that my ‘test powersupply’ is putting 70ma across the base of thewhich is saturating it. Its datasheet is very old and it doesn’t explain function of the IC well.

This is confusing too. I feel well past dstasheet depth trying to sort this out The LM’s datasheet is at http: Email Required, but never shown.

Problem with LM Tach Circuit – 14 Pin version

The output transistor is provided with open emitter and collector to permit its use in a variety of configurations. C42 does two things – the higher the value the lower the ripple voltage will be seen at the output however, the longer it will take to attain the correct voltage should the frequency change. I need a circuit which generates 1mV voltage per 1Hz frequency.

I then have another supply, also grounded to the common ground, thats 14V. I think l2917 problem lies with the input circuitry of the LM If I pulse 14V onto the “Signal In” port with that powersupply also connected to ground I’m guessing the AC input is required to be centered on 0V, incidentally, but a DC blocking cap outside the chip would easily achieve that.


This is the capacitor the charge pump is charging. Its driving me nuts I’m hoping someone can take a moment to help me and possible restor my sanity! I think the problem is my Internal Zener references. How are you pulsing the 14V?

Ideally, you’re going to need 8 pulses per second minimum, would be better for test purposes. The charge pump is charging a capacitor which one?

National Semiconductor

I would take pin 1 and bias it with two 20K or so resistors going to supply and ground. I created a custom library for this IC and set up my own circuit as seen in the schematics above. I’m not game to hook it to my ‘duino nor can I be buggered going out to the bike yet I’ve substantially edited this text to make it more true, see the edit history to see my incorrect babbling if you really want to.

Since the chip was originally built to post-process a magnetic pickup for tachometer applications, the zero crossing would be easy to arrange for by directly wiring the pickup coil across pins 1 and 8.