LM2917 not working

Using Arduino Sensors
#1

Hi,

I’ve been struggling to get LM2917 work but, no luck (all i am getting is 0v at pin-5). There’s not enough documentation for 14pin version of chip. I have attached the circuit diagram. Could anyone please take a look and see if i am doing something wrong?

I have generated a 1Khz square wave using arduino due and haven’t used any coupling circuit at the input pin of lm2917 (connected directly). Also arduino due outputs 3.3v means, lm2917 is getting 3.3v square wave at pin-1 (i think input signal range of lm2917 is 0-28V , so this should not be a problem).

Any help will be appreciated.

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#2

First things first.
1-Where did you get the schematic you posted ?
2- Did you read the datasheet ? (see attached)
3- How can you explain the fact that you have no resistance from pin -5 to ground (see Figure 23 & 24 on page 11.

lm2907-n.pdf (2.14 MB)

#3

I have a 10k resistance at pin-5, not shown in the diagram. I used same circuit as described for the lm2908-8.

#4

I used same circuit as described for the lm2908-8.

Produce a datasheet for that chip.

(The only LM2908 I could find is an op amp. see attached)

You didn’t answer these questions:

Where did you get the schematic you posted ?
2- Did you read the datasheet ? (see attached)

Where did you get your schematic ?

LM2908 (1).pdf (55.6 KB)

#5

Hi,

never mind i got it working. problem was, i was testing it with 3.3v square wave but actually it worked with 5v.

#6

If you have an arduino DUE you must know by now that you need level shifters . What chip do you use to do that ?

#7

Hi,

you are right! but this is my first time working with 3.3v micro controller board and i probably forgot about it. (thats why i am using lm2907 for this purpose, also it takes the load off of the micro controller)

I am testing LM2917 as shown in the attached diagram with a 5V square wave generated by the signal generator and it is working fine. As I change the frequency it responds quickly.

Problem is when i hook it up with the hall sensor pickup circuit http://www.sensing.honeywell.com/honeywell-sensing-ss41f-ss41g%20series-product-sheet-005889-2-en.pdf (which gives me one pulse per revolution), it does not work. then, i though it might be because of the impedance mismatch and inserted a op-amp buffer in between the hall sensor pickup circuit and input of the lm2917 but didn’t work.

crazy thing- just for curiosity sake i inserted op-amp buffer in between the signal generator and the lm2917 input, guess what…didn’t work. i don’t know whats wrong here.

Any suggestions?

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#8

Try a comparator signal conditioner circuit between the hall effect and the Lm2917.

#9

Hi,
Thanks for reply. i will try. but so that you know hall sensor that i am using can provide unto 20mA of source current that should be enough to drive the lm2917.

#10

Then the resistor shown across it should be 200 ohm right ?

#11

I think thats where I am wrong. I put 10k resistor between the output and supply.

#12

Are we talking about the same thing ? I'm talking about the resistor in your schematic across the hall effect sensor that has no value shown . Is that 10k ? (please tell me it's not).

#13

it is. i'll c hang it with 200 ohm and see what happens.

#14

Why 200 ohms ?
Let's see now,
E = I x R
Let I = 0.020A
Let R = 200 ohms
E = I * R = 0.020 * 200 = 4V.

#15

Right! Im using 5v supply so i can use 250?

#16

yes you can.

#17