How to convert .1 volt step to 3.3 volt logic high

dl324

Joined Mar 30, 2015
12,871
Welcome to AAC!

You need to describe what you mean by "a very small voltage step". 0.1V step from what to what? Just one "step"?
 

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NOPdowop

Joined May 21, 2021
20
I need to detect a current pulse of 1 mA. I plan to use a 100 ohm sense resistor to develop .1 volts. I need to know every time 1 mA flows. My micro power PIC has no ADC. The circuit has to run a year on AA batteries.
 

Thread Starter

NOPdowop

Joined May 21, 2021
20
diff amp, line receiver, opamp, comparator, A/D converter and perhaps others too numerous to mention.
Unmentioned is my original question was the micropower requirement. Sorry, I forget how many details are needed to explain the whole situation.
 

Thread Starter

NOPdowop

Joined May 21, 2021
20
I ordered in some MAX9934 chips, but the uMAX-8 buggers are SO TINY I doubt I will be able to hand solder them in small quantities.
 

Papabravo

Joined Feb 24, 2006
16,107
Unmentioned is my original question was the micropower requirement. Sorry, I forget how many details are needed to explain the whole situation.
Design problems can be tough when you're deprived of FTF interactions. We used to spend hours (cumulatively, not all at once) over coffee just spit-balling over various problems. Once the boss understood the purpose, he asked if he could join us. It was a wonderful time.
 

djsfantasi

Joined Apr 11, 2010
7,689
So do you expect to detect a voltage change without a means to detect voltage?

You need an external ADC if your uP does not have one. If the voltage reference of the ADC is Vr, and the number of bits of the ADC (2^nbits) gives you a step voltage of Vr/(2^nbits) which is less than or equal to 0.1V, then you can detect your required situation. If the step is 0.01 through 0.05, then all the better!
 

ericgibbs

Joined Jan 29, 2010
12,901
hi NOP,
What is the driving source of this 1mA current.?

Do you have a simple sketch to post, showing the location of the 100R in the circuit.?

E
 

sparky 1

Joined Nov 3, 2018
541
Having a 100 millivolt logic signal and level shifting to 3300 millivolts or 3.3V I think keyword(s) might be " level shift ".
Deciding on which level shifting, that takes experience. If you are doing a really nice job it becomes necessary to ask for more details. Understanding which details to ask for depends on which solution you decide on. For that reason later it is common to need yet more unforseen details. There are different styles of changing horses in midstream the wagon master sometimes
has to expect some unforseen problem could appear.
 

Thread Starter

NOPdowop

Joined May 21, 2021
20
I am sorry to be doing this so poorly. I can see now that everything I have in my own head is not in the cloud as well. I apologize for being annoying. Let me see if I can provide a better picture. I am using a PIC12C509. I know it's old, but for historical reasons I would prefer to use it. I am writing in Parallax syntax assembler and the tools I have were current when that was current. My tools won't support the most recent chip families. I am evolving a project written 20 years ago and I would prefer to use the code I already have, though PIC assembly code is pretty portable within the (old) Microchip universe. The feature I need to add is the ability to detect when an external device turns on. The external device draws 1 mA from a power supply that is not the same as the power to the PIC chip. I can afford to drop a tenth of a volt from the external device, but I can't afford to drop too much more than that. I have been planning to use a sense resistor above the load to develop a voltage of .1 volts. The external device is active for about 100 mS about once a second. Since the device must run on AA batteries for about a year, everything must be pretty low power. The PIC is running at 96 KHz and needs to for low power. I had hoped to use the MAX9934 current sense IC but the package is just so damned small. I thought it might be possible to use a differential opamp (which is how the MAX9934 works), but I am unable to design the circuit. I was hoping there might be some more simple way to do this, with a mosfet maybe, but my experiments have not worked out.
 

dl324

Joined Mar 30, 2015
12,871
I need to detect a current pulse of 1 mA. I plan to use a 100 ohm sense resistor to develop .1 volts.
All you need is a comparator to detect when the voltage is around 0.1V.

I say around because you want to give yourself some noise immunity. If the current in the sense resistor is either 0 or 1mA, you can pick the mid-point - 0.05V. That's high enough that you won't need to worry about the comparator's offset voltage.

LM393 will give you a common mode input range that includes ground.

EDIT: This circuit will give you a 5V output when the current is present (voltage at non-inverting input is 0.05V or higher):
1621624743738.png
 
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dl324

Joined Mar 30, 2015
12,871
The LM393 draws too much current to run for a year. I need microamps.
Here is a block diagram of what my plan was.
You should have mentioned that requirement in your original post so we don't waste our time trying to solve a poorly defined problem.
 

dl324

Joined Mar 30, 2015
12,871
I will look for a micropower opamp with which to implement this design.
You can make the resistors on the voltage reference an orders of magnitude larger. The output depends on what it will be driving. You could switch to one with an active output. Just make sure the common mode input voltage range goes low enough.

What type of battery are you going to use? Is there the possibility of charging it with a solar cell?

More relevant information will let us take those factors into consideration. Otherwise, the solution space is wide open like it was with your first couple of posts. As others like to say, we're not mind readers and most of our crystal balls are out for repair...
 

Thread Starter

NOPdowop

Joined May 21, 2021
20
This was my first request for design help on a forum, and I just didn't slow down enough to consider everything involved. I'm very sorry to have been so inadequate. I will breadboard your design to confirm operation, then order in an opamp that meets my special needs.

I had wondered if I could use a sensitive Hall effect device and a small inductor to generate enough magnetic field to trigger it.
 

LesJones

Joined Jan 8, 2017
3,172
If you could change from the PIC12C509 to PIC12LF1840 or similar modern device that would reduce the power consumption and it also has a built in analogue comparator which you could use to detect the 100mV voltage change

Les.
 
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