Please Help!!!! LM2907 Speed Switch

Your description of the component values you are using is confusing to me. Is it possible that you could post a schematic of what you are working with, that includes the parts values on the components, so we don't waste a lot of time on a misunderstanding?

The sine wave makes no difference, since the input is just going to a comparator anyway. However, the sine input must be centered on 0. If you are giving it 0 to 5V, it won't work, since the comparator in the LM2907 compares against 0. So, put a cap in line with the sensor output, and a big resistor (like 1MEG) from the chip to center the input on ground.

Also, the timing capacitor is on pin 2, I think, and the one on pin 3 is used stabilize the output voltage. So, the resistor on pin 3 is R, the cap on pin 2 is C, and the thing will go on when f >= 1/(2*R*C).

The resistors between 6&7 and 7&8 aren't critical, but the data sheet uses

5k, so I'd go 4.7k for these. They are supplying a switching voltage. I suppose you could use a pot to change the voltage at which the output switched. (see below)

If you want it to switch on someplace between 10 and 100Hz, use C = 1uF, R = 10k, the stabilizing C (at pin 3) at 0.1uF, and put a 10k pot between Vcc and ground, with its wiper connected to pin 7. (instead of the fixed

10k resistors). You should then be able to adjust the switching frequency by changing that pot. I think that works.

--
Regards,
  Bob Monsen

Let us grant that the pursuit of mathematics is a divine madness of the
human spirit.
- Alfred North Whitehead

oneday i tryed to make this circuit and i have failed , it is energizing the load when the frequency is LOW not HIGH than Fin !!!

so , there is a very good solution for you make a simple frequency to voltage converter circuit with this IC and then use a comparator to compare the output of the LM2907 with thedesired voltage and then take the output of the comparator to run a transistor to run a relay to run whatever you want.

may be i could not explain it good but it is so easy to make.

Thanks for all the help. I will put all this to the test. First does anyone know of a good company to buy all these parts from. Thanks for all the inputs and i will surely keep everyone posted on my success. Again Thanks

Eddie

Change it to .01 uF

Change it to 1 uF

No, it isn't. If it was 500K ohms, the lights would never glow.

The other two resistor's are

After you have made the component changes mentioned above and tested things, post the schematic with ALL the components shown and labeled with their values, as John requested. We can't do more than make very general comments without correct infromation.

By the way - I suspect that once you get it working, it will work backwards, turning the lights on when you want them off, and vice-versa, based on what you've said. That's a simple matter to address - but we have to wait until you get the LM2907 circuit sorted out.

Ed

By the way , does the LM2907 output is perfect linear ? i have tchometer circuit with 33000 R and C1 is 0.094 uF and C2 is 2.2 uF i made the calculation of this formula.. Vout=Vin *C*R*Fin and i want it to work from zero to 166 Hz so Vout=8*0.00000009*33000*166= 3.9 then i have an LM3914 circuit with low reference is zero volts and high reference is 3.9

will that work ? i mean will the LEDs of the LM3914 run from zero to

3.9v or the LM2907 output rate will increase to over 3.9 while increasing the RPM ?

Thankx :)

That is the way I read the formula, though where you got a 0.094 uF capacitor I can't guess.

Yes, the LM3914 should indicate linearly from zero to whatever voltage you connect to the high reference pin. But I think if your cap really is 0,094 uF, you should calculate with that number. Or make the upper reference a bit adjustable so you can trim the full scale by experiment.

the cap. is .074 + .047 uF connected in parallel. i made it today and the result was very good . next step is to connect the comparator-transistor-relay circuit to make the shift light :)

honestly, i made all that and learned many things in electronics because of the good guys in this forum especcialy ED(ehsjr) Jonathan Kirwan , Jon Poplish and more :)

Thanks you very much.

I checked the resistor that i have in series with the load and it is

510K. The color band is as follows. Green, Brown, Yellow and then gold is the last color. What rating do you recommend for that resistor. Thanks Ed

Maybe we're lost in terminology. The load is the light that you want to turn on and off with the LM2907. If it is in series with 510K, and the supply is at 12 volts, current will be limited to no more than ~ .0000235 amps.

23.5 microamps through a lamp at 12 volts is not going to make it glow. So something is wrong with the description.

Ed