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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That chip is made to detect RPM, most engines Idle rpm-ish, so you’re going to datasheeg a bunch of pulses or it’s going to measure 0.

Problem with LM Tach Circuit – 14 Pin version

All the capacitors and resistors are connected to ground; I’m very confused at this step. It just gives several example circuits and a formula for the output voltage. Post as a guest Name. C42 does two things – the higher the value the lower the ripple voltage will be seen at the output however, the longer it dahasheet take to attain the correct voltage should the frequency change. R46 is acting as a load for the charged signal. You want it to keep the measurements stable. As you’ve wired it, the feedback acts to keep the voltage on pin 4 equal to the voltage on pin 3, with far better drive aka lower output impedance than offered by the output of the charge pump tachometer stage alone.

I datzsheet well past my depth trying to sort this out RBerteig 6 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 played around with a few variations. Email Required, but never shown. I think the problem is my Internal Zener references. I have then used the datasheet as well as this schematic to convert to 14 pin I’m guessing the AC input is required to datqsheet centered on 0V, incidentally, but a DC blocking cap outside the chip would easily achieve that.


Sign up using Facebook. Its driving me nuts The datasheet indicates a typical use case for the chip being to light a warning light when input frequency exceeds a threshold, in which case having an output transistor capable of sourcing or sinking more current makes sense. Pin 11 and Pin 1 are the two inputs of a voltage comparator. Can anyone offer some guidance?

The first op-amp is a camparator as your question states. The second op-amp is buffering the signal stored on C41 and driving the output transistor, it has feedback from the output to its -ve input which is a common configuration for a unit-gain buffer.

National Semiconductor

Therefore to get the chip to do anything you have to take pin 1 above and below this point. Sign up or log in Sign up using Google. I created a custom library for this IC and ml2917 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 Im guessing now totally that my ‘test powersupply’ is putting 70ma across the base of thewhich is saturating it.

The output transistor is provided with open emitter and collector to permit its use in a variety of configurations. Andy aka k 10 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 C40 is being charged by dumping charge into it at each zero crossing or perhaps at one edge only of the AC input.


I’ve built this on a breadboard using a modified version of dataeheet 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 lmm2917 pickup coil across pins 1 and 8.

Then you stand a chance of getting the input to switch. Read towards the bottom of page 8 on the data sheet. To help save hands, I hooked an LED up to the output signal.

Sign up using Email and Password. It is drawn to be a comparator rather than a buffer. And heres my breadboard layout: 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 The LM’s datasheet is at http: I think you problem lies with the input circuitry of the LM Once it stops raining here, I’ll drag it out and put it onto the bikes injector dtaasheet at least and see if that makes it datashest better Home Questions Tags Users Unanswered.

An example circuit from the datasheet.

Then put a 10K resistor to the cathode of D3 and the other end of it to ground. If I pulse 14V onto the “Signal In” port with that powersupply also connected to ground The sig-in line goes from 5. Its datasheet is very old and it doesn’t explain function of the IC dqtasheet. But how does this charge pump do this? What is the function of the second opamp?

C41 is a filter capacitor to reduce the ripple from the charge pump.