Frequency to voltage converter lm2907 ground connection

Thread Starter

Tony Elliott

Joined May 8, 2015
144
Hello All About Circuits,

I am using a square wave oscillator 555/4013 (powered by 9v battery) connected to a LM2907 frequency to voltage converter (12v - ground +).

I have taken the positive from the audio out and put it into the frequency in (Fin) as you can see in the schematic. I am getting a responsive reading on my multimeter (by varying the oscillators frequency) without ground connected from audio out. 0 - 1.8 khz 1 - 2.4 dc
When I connect ground I get nothing. On the schematic, frequency in (Fin) am I doing something wrong in my connections??

circuit on page 10
http://www.ti.com/lit/ds/symlink/lm2907-n.pdf
 

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Veracohr

Joined Jan 3, 2011
715
I've never used something like this so I'm not sure, but you've got -12V on the negative input to the comparator so I wonder if it is able to do anything. Your input signal doesn't go below -12V does it? With the circuit connected as shown in the datasheet, the negative comparator input is ground, so it is sensing the 0-crossing point of the input signal.

Try removing the -12V and just ground those pins like the circuit in the datasheet.
 

Thread Starter

Tony Elliott

Joined May 8, 2015
144
I've never used something like this so I'm not sure, but you've got -12V on the negative input to the comparator so I wonder if it is able to do anything. Your input signal doesn't go below -12V does it? With the circuit connected as shown in the datasheet, the negative comparator input is ground, so it is sensing the 0-crossing point of the input signal.

Try removing the -12V and just ground those pins like the circuit in the datasheet.
It doesn't go below -12v. What you said sounds interesting. You mean attach the ground from the 9v circuit to the -12v in the comparator? I'll try it
 

BillB3857

Joined Feb 28, 2009
2,533
The reason I asked the question was that some will tag a voltage as though it were the negative end of a battery, ie a single 1.5 volt cell will have a +1.5V and a -1.5V. Throwing a ground into the mix will require TWO 1.5v cells. Just to clarify, do you indeed have a +12, GND and -12 supply?
 

Thread Starter

Tony Elliott

Joined May 8, 2015
144
I've never used something like this so I'm not sure, but you've got -12V on the negative input to the comparator so I wonder if it is able to do anything. Your input signal doesn't go below -12V does it? With the circuit connected as shown in the datasheet, the negative comparator input is ground, so it is sensing the 0-crossing point of the input signal.

Try removing the -12V and just ground those pins like the circuit in the datasheet.
I tried doing this and there was no voltage reading.
 

Thread Starter

Tony Elliott

Joined May 8, 2015
144
I think Ive solved this, I turned the 9v battery oscillators power into two 9v batteries with 100 uf capacitors and made it into a dual battery power with - ground + and attached the ground between circuits and I have a much more stable reading on my multimeter.
 

Veracohr

Joined Jan 3, 2011
715
It doesn't go below -12v. What you said sounds interesting. You mean attach the ground from the 9v circuit to the -12v in the comparator? I'll try it
No, I meant don't use the -12V supply. Replace it with ground (common from your +-12V supply), to which you would also attach the negative terminal from the battery. There's no reason to use the -12V supply, only the +12V.
 

Thread Starter

Tony Elliott

Joined May 8, 2015
144
No, I meant don't use the -12V supply. Replace it with ground (common from your +-12V supply), to which you would also attach the negative terminal from the battery. There's no reason to use the -12V supply, only the +12V.
Yes you were right I used the ground from the 12volt supply with the battery circuit using only one battery instead of two, it worked when I put the ground where the minus and the minus where the ground is on the battery circuit strange really? I used 104 capacitors to bridge to smooth
 
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