Questions about LM2917 frequency to volts converter

[potoole64]

(1) Should the input be AC (cycling above and below ground)?
(2) Can the input be pulsating DC (pulses that go from hi to lo voltage riding on central DC)?
(3) What voltage should the power source be, since the 2917 has a 7.8v zener diode

I want to read pulses taken from a Motorcycle ignition from the same point that the tachometer is fed from. I'm not sure, but I think the pulses are above ground pulsating DC. I use a voltage divider to lower the ignition voltage to about 4v. The pulses range from about 30 to 150 per second. I don't have an oscilloscope, but I 'capture' the pulses by using a cheap sound recorder, then apply the pulses to a sound card oscilloscope that I downloaded from the internet. I'm not sure what the p to p volts. of these pulses are as the sound card osc. doesn't really show this. When I apply these pulses to an LM2917 ckt., set up as basic freq. to volt. converter, I get 0 (or a very low voltage) as an output. I've tried different configurations for the input cirduitry, resitive/capacitive inputs with coupling caps. of different sizes, even direct input. I've tried different power source voltages from 3v to 9v. Can't seem to get things working.

(4) Is the freq. of the pulses too low?
(5) Do I need a higher volt power source?

thanks for now
PO'T

 

[crutschow]

(1) (2) The input can be configured for either a pulsating DC from above ground to ground or a signal that goes above and below ground. But you need to determine which type your signal actually is.

(3) The 7.8V zener means you need to add a resistor in series with the power pin to the LM2917. You must never connect a zener directly to a supply voltage. The data sheet recommends a 470 ohm resistor for a 9V to 16V source which should cover a standard motorcycle 12V battery variation. If you connected the power directly without the resistor you may have zapped the chip (reading the data sheet completely first can prevent all kinds of problems).

(4) Operational frequency is determined by the value of R1, C1, and C2 used.

(4) 12V is good if you add the 470 ohm resistor in series.

 

[audioguru]

(1) Should the input be AC (cycling above and below ground)?

The datasheet says the 8-pins versions of the LM2907 and LM2917 must have the input swing above and below ground and exceed the threshold voltage for variable reluctance pickups.
The 14-pins versions have a differential input so the user can select his own input switching level and still have some hysteresis.

(2) Can the input be pulsating DC (pulses that go from hi to lo voltage riding on central DC)?

No. Add an input coupling capacitor feeding your voltage divider at the input.

(3) What voltage should the power source be, since the 2917 has a 7.8V zener diode

It is obvious that you didn't look at the datasheet where they show a current-limiting resistor feeding the zener diode and talk about it.

I want to read pulses taken from a Motorcycle ignition from the same point that the tachometer is fed from. I'm not sure, but I think the pulses are above ground pulsating DC. I use a voltage divider to lower the ignition voltage to about 4v. The pulses range from about 30 to 150 per second. I don't have an oscilloscope, but I 'capture' the pulses by using a cheap sound recorder, then apply the pulses to a sound card oscilloscope that I downloaded from the internet.

You need a DC-coupled oscilloscope, not an AC-coupled recorder/sound card.
It will probably work if you use a coupling capacitor feeding your voltage divider.

 

[potoole64]

The 2917 was connected to components and power source as shown in the data sheet. including the 470-ohm resistor connected between power and pin 6. (or 9 on the 14pin chip). I should have mentioned that I have one of each: an 8 pin and a 14 pin lm2917. On the 14pin, Pin 3 is seperated into 3 and 4, pin 5 is the same as 4 on the 8pin, 8,9,10 are the same as 5,6,7 respectively and pins 11,12 are ground. Pins 6,7,13,14 are not used. I did read the data sheet, but not the whole thing, apparantly. The eight pin might be wasted, but I was more careful when doing the 14 pin.

Thanks for the info. I will add an input coupling cap. to my volt divider, and I see that Carls Electronics has a ST16B Low Cost Oscilloscope
This is a very affordable oscilloscope, designed with the hobbyist and traveling professional in mind. For a hundred and fifty bucks. I'll try to scrape that up, the hundred and fifty.
PO'T

 

[sriniooty]

Hi i'm srinivasan.
I tried to convert Frequency to voltage converter by using LM2917 which was given in the datasheet of LM2917 (14 pin)(13 th page example.) While i'm testing the circuit the IC getting heating up. I don know the reson too. I tried to debugg the ckt. But same thikg was happened.. Please anyone help me to solve this problem..

 

[audioguru]

I tried to convert Frequency to voltage converter by using LM2917 which was given in the datasheet of LM2917 (14 pin)(13 th page example.) While i'm testing the circuit the IC getting heating up. I don know the reson too. I tried to debugg the ckt. But same thikg was happened.. Please anyone help me to solve this problem..

The lM2917 has a 7.54V zener diode inside at pin 9 to ground. The circuit you are using on page 13 of the datasheet shows the LM2907 that does not have the zener diode.
You are overheating the zener diode without using a 470 ohm resistor feeding pin 9 from 14V.

The pin numbers on page 13 show the 8-pins IC so you must translate everything to use the 14-pins iC.