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 ?
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.
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.
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 ?
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 ?
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.??
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).
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.
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.
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.
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 !) ?
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.?
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)...
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.
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.
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.
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 !
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.
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 ?
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.