Hos to trigger this input ?

[schneiderj]

How to trigger this input ?

Hello !!

Happy new years every body !

I have a signal coming from a coil and the best I have found to have it is imply to amplify it with a INA128 (white curve). Almost nos noise and even at 1 meter I have more than 1 volt.

Now I would like to input that signal to a PIC. I try to use a diode to eliminate the negative part of the signal (a 1N4148), but I did not obtaine what expected (green curve).
What I am doing wrong ?

I have a second question : is it possible to use this signal (+/-5 Volts) with a CI like 74HC132 to have a nice digital signal ?

Thanks you for your help,
Jean-Marie

 

[ericgibbs]

hi,
Please post a diagram on how you have connected the signal, diode and PIC.

 

[schneiderj]

hi,
Please post a diagram on how you have connected the signal, diode and PIC.

I can't for the moment : I don't have access to the first floor of my haus (fresh paint on the staires). But what your question probably give me the answer : the diode is not connected for the moment... or more precisely only on the output of the INA.

That could be my problem... ?

Jean-Marie

 

[ericgibbs]

I can't for the moment : I don't have access to the first floor of my haus (fresh paint on the staires). But what your question probably give me the answer : the diode is not connected for the moment... or more precisely only on the output of the INA.

That could be my problem... ?

Jean-Marie

hi,
If the diode circuit is incorrect or incomplete it will not rectify the sine wave.
So when you can please post a diagram so that we can help.

 

[schneiderj]

Hello,

Would you find the schematic of what I am doing. I have made the junction between the 0 volt and the diode. Now it is working (see picture).
Thanks for your help.

As there is almost no noise in the signal, I would like to use it directly without filter (sending it to a 74HC132 as said before) . Is that a good idea ?

Jean-Marie

 

[ericgibbs]

Hello,

Would you find the schematic of what I am doing. I have made the junction between the 0 volt and the diode. Now it is working (see picture).
Thanks for your help.

As there is almost no noise in the signal, I would like to use it directly without filter (sending it to a 74HC132 as said before) . Is that a good idea ?

Jean-Marie

hi,
The trace shows a peak voltage of about +3.2V, this should be high enough to switch the HC132 OK, when using a +5Vsupply to the HC132
What are you going to use the output of the HC132 for.??

 

[schneiderj]

I would like to have my own cardiofrequencemeter with some function which are available only on more expensive one.
There is a message where I have explain that project : https://www.electro-tech-online.com/threads/how-to-design-an-antenna.84693/

The INA128 give me the best signal with almost no noise, but for an outdoor application the symmetrical power could be a problem. I have take a look with an unsymmetrical powe (0/+5V). I have ordered a TLC081, to see if I can obtain better results... but that poor result come probably from the scheme I use to perform this amplification (see attached picture).

Jean-Marie

 

[ericgibbs]

hi,
If you used a 9V battery, its possible to split the supply for the 1NA120 into about +/-4.5V using a virtual earth.
If you the use a LM393 comparator to square up the signal [ instead of the HC132] this will give a better result.

Do you follow OK.?

 

[schneiderj]

Hello,

why are you suggesting the INA120 ? I can also use a virtual earth with the INA128...
I have found on the Texas site that the INA1220 is no more existing, but is replaced by PGA204. I will read the datasheet.

For the LM393, I don't know (in fact I have limited knowledge in electronic : I am a chimist !).I will read the datasheet as well.

Jean-Marie

 

[ericgibbs]

Hello,

why are you suggesting the INA120 ? I can also use a virtual earth with the INA128...
I have found on the Texas site that the INA1220 is no more existing, but is replaced by PGA204. I will read the datasheet.

For the LM393, I don't know (in fact I have limited knowledge in electronic : I am a chimist !).I will read the datasheet as well.

Jean-Marie

hi,
I have thought that you would have realised that the 1NA120 was a typographical error. To clarify I mean the 1NA128.

 

[schneiderj]

Hello Eric,

Finally I am expecting to have somethink not to bad without the expensive INA128.
I try with a TL084 (but I will order TL082 tomorrow), and obtain interesting results with the attached scheme. I take two picture of the signal after amplification and after comparison at two distances.

Can I have your feedback on these results (and from Audioguru if he read this topic, as he help me a lot to learn the antenna design !) ?

Thanks you for your help,
Jean-Marie

 

[ericgibbs]

hi,
It looks OK to me, I see you are using the 2nd stage as a threshold detector.
You have the threshold set a little too high, its clipping above the zero cross over.
What will the output of the 2nd stage be connected into, how will you use these pulses.?

 

[schneiderj]

hi,
It looks OK to me, I see you are using the 2nd stage as a threshold detector.
You have the threshold set a little too high, its clipping above the zero cross over.

Thanks for your very fast reply !!
I don't understand why you are saiyng "its clipping above the zero cross over". I have set the threshold at arround 1.3 V and the power is between ground and +5V. Did you think that 1.3 V is to hight ? I take this value to avoid noise which some time is not far from 0.5 V. What will be better ?

What will the output of the 2nd stage be connected into, how will you use these pulses.?

I will probably connect it to a 18F (probably a 2520) to RA4 to use the TMR0 as a counter. But not such yet, I have to look if i have better solution (PORTB is dedicated to drive a LCD excepted the RB0)...

Jean-Marie

 

[ericgibbs]

hi,
If you make the threshold setting resistor a variable, it would be possible to set the threshold to suit the noise levels in different environments.

Providing the Voutput swing of the signal changes below the PIC limits as a logic 0 and above logic 1, the PIC should count the 5KHz signal pulses OK.

 

[schneiderj]

hi,
If you make the threshold setting resistor a variable, it would be possible to set the threshold to suit the noise levels in different environments.

Yes !! that a good idea.

Thanks
Jean-Marie

 

[audioguru]

Hi Jean-Marie,
1) The minimum supply voltage for a TL082 is 7V and it might not work with only 5V.
2) The input common-mode range for a TL082 is 3V more positive than ground in your circuit. Since your input is connected to ground then whenever the signal is less than +3V the output will go high because the TL082 has the Opamp Phase-inversion problem.
3) The circuit might work with an MC34072 dual opamp. Its minimum supply voltage is 3V and its input common-mode voltage range includes ground in your circuit. It has about the same high speed as the TL082.

 

[schneiderj]

Hello !

I am a little bit confuse : I use the TL082 for the schematic, but in the real world I use the TLC082 which had a single supply...
And fortunately I don't have TL082 or TL084 on the shell... but I am a little worried as TLC are more expensive !

What did you think about TLC082 ?

Thanks
Jean-Marie

 

[audioguru]

The TLC082 is completely different to the TL082. I wish you showed it in your schematic.
It will work fine but it might oscillate if it drives the capacitance of a shielded cable. The datasheet recomends adding a resistor in series with the output to isolate a capacitive load.

 

[schneiderj]

Thanks for these explanations.

I have an other question regarding the choice of an AOP.
When I read some general book or article found on the web, every thing is simple. But it seams that in the real life think are more complicated.
So how I guy as me with only limitated knowledge in electronic can do to select an AOP without to much error ?

Jean-Marie

 

[audioguru]

Hi Jean-Marie,
You will quickly learn that most old opamps don't work at low supply voltages.
The lousy old 741 opamp is 40 or 41 years old and is specified only with a 30V total supply voltage. Some work with a supply as low as 10V but some don't.

Supply voltage, supply current, input current, inpit common-mode voltage range, max frequency and noise level are all things that you should consider when selecting an opamp.