Double Micro (nano) Ampere meter

[sundberg84]

@AWI - did you steal my image on my workbench ;) j/k.
We need to revive the old workbench topic again!

[gohan]

Are resistor needed with a tight tolerance or else?

[AWI]

@gohan No special tolerance resistors needed. The only reason for choosing metal film resistors is that their temperature coefficient is better than carbon types (typical 50ppm/°C compared to 200-500ppm/°C).
As you will be calibrating the circuit you can choose from a large range (0.1 Ohm - 100 Ohm) for the shunt. This will only influence the burden voltage / sensitivity and range (Ohm's laws).

[DavidZH]

@AWI Lemme think about that..... Uuuuuhm. no... 😈

I have no plans for a meetup. Lacking a proper venue for such a thing. Unfortunately.

[NeverDie]

If there is some interest I will try to publish a decent built instruction on Openhardware.io.

I'm interested.

[Nca78]

@NeverDie said in Double Micro (nano) Ampere meter:

I'm interested.

In case you haven't seen it, it's here :
https://forum.mysensors.org/topic/6723/micro-nano-ampere-meter-double/5

[NeverDie]

@Nca78 said in Double Micro (nano) Ampere meter:

@NeverDie said in Double Micro (nano) Ampere meter:

I'm interested.

In case you haven't seen it, it's here :
https://forum.mysensors.org/topic/6723/micro-nano-ampere-meter-double/5

Thanks! It looks a bit complicated to me. I've used one of these breakout boards (https://www.amazon.com/gp/product/B00OPVBEQO/ref=oh_aui_search_detailpage?ie=UTF8&psc=1) as a way to measure 24-bit voltage on capacitors, and it works really well. As you can perhaps tell from the photo:

the chip is fairly simple to use. What I especially liked is that there was already a demo arduino sketch for interfacing with it. That was a real time saver. If I were to build something, I might try that first, if only because it seems like it might be easier (though perhaps, in part, because I'm already comfortable with it). Would using it in conjunction with a sense resistor be all it would take to make an accurate, high resolution current sensor?

[AWI]

@NeverDie that one would work as well. Maybe harder to get and a little more pricy :moneybag:

[AWI]

@NeverDie said in Double Micro (nano) Ampere meter:

It looks a bit complicated to me

btw. Which part looks complicated? It's just a few resistors attached to an ADC board (and sketch ready) I am curious on how you can build something simpler with the ADS1220 (which seems to be a better ADC if you are able to find it somewhere ;-))

[NeverDie]

It sounds like I was mistaken then. In my quick read I thought that I had to implement the entire schematic, not just add a couple of resistors to a pre-made breakout board. I suppose if the schematic were more of a block diagram, that might be clearer for other future readers to quickly grasp, or maybe it's just me.

Why would the ADS1220 be a better ADC? I really haven't looked into doing a comparison. I bought the breakout board that I pictured above from Amazon , but I see that it's out of stock now. I believe the company which made it is in India. I seem to recall that it's open source, so there's always that I suppose. I didn't mind ringing the till for the maker: it was all pre-made, it did what I needed at the time (which was watching in real-time the voltage leakage from supercapacitors that I was testing), it was available with free Amazon Prime delivery, and I wanted something sooner rather than later. So, it fit what I needed at the time. Most of those reasons relate to rapid availability though rather than technical reasons.

[NeverDie]

OK, I received an HX711 and have partially hooked it up. I have it connected to an UNO and powered by the 3.3v pin. I also have AWI's sketch running on the UNO. I haven't yet connected a OLED screen to it, so at the moment I'm just looking at the output of the serial consol, which gives a running output of "average" and "spread". I have 10mv connected between A+ and A- to just to see what it will do.

Looking at the code, it looks as though the button (A2) is normally pulled high. Is the button supposed to be connected to GND through a 330 ohm resistor? I don't see any schematic with a button on it.

[mfalkvidd]

@NeverDie the sketch uses the internal pullup:

Button myBtn(buttonPin, true,  true, 40);				// Declare the button( pin, pullup, invert, debounce ms)

[NeverDie]

@mfalkvidd said in Double Micro (nano) Ampere meter:

@NeverDie the sketch uses the internal pullup:

Button myBtn(buttonPin, true,  true, 40);				// Declare the button( pin, pullup, invert, debounce ms)

Right. So that's one leg of the button. Is the other leg connected to GND through a 330ohm resistor? Or....?

[mfalkvidd]

@NeverDie sorry. Of course you knew that already :)
I found this in the instructions:
Solder the Button to A2 and Gnd of the nano
I guess that means the other leg is connected directly to GND, no resistor is involved there?

[NeverDie]

Thanks. I'll do that then.

Regardless, I must be doing something wrong, because I'm feeding it 9.9mv (see photo)

across A+ and A- from a voltage divider powered by 2xAA batteries, but it's showing zero current. Shouldn't it be showing 9900ua instead?

[I alsoi tried sending it 99uv instead, but it still reads zero]

[NeverDie]

So, here it is with the button and with 99uv applied.

Button mechanics works fine, but it keeps registering zero as the uA. Isn't it 1uv=1ua? So, shouldn't it be reading 99ua? Or am I (quite probably) misunderstanding something?

The HX711 I'm using is a clone of the Sparkfun one.

[NeverDie]

I added in the 0.1uF cap across A+ and A-, but that made no difference.

What's odd is that if I run the sparkfun scale code, it does in fact detect voltage (and converts it to pounds). Hmm.. Sounds like maybe it's not reading the right datapins. I'll check that next.

[NeverDie]

Yup. That was my error. I had initially wired it using the sparkfun directions for the initial test. Sparkfun wired the DAT and CLK pins to different arduino pins. When I made the change to AWI's selections, it now works. :)

[NeverDie]

By the way, there was a similar project posted on the eevblog by a guy named quantumvolt:
https://www.eevblog.com/forum/projects/ppmgeek!-5-5-digit-dvm-volt-ref-cal-(for-arduino-or-any-uc-w-spi)/
One of the things that they eventually noticed and talked about was that quite a bit of noise came in over the usb. Not sure if that applies only to usb's connected to computers for power, or whether it may apply to other sources as well. Anyhow, just thought I'd mention it in case anyone here is using that and wants to drop their noise level.

Also, although I'm no expert, I would guess this project might (?) benefit from a PCB implementation, because, in general, it seems like the shorter the connections, the lower the noise. Of course, please just take that as constructive feedback. No criticism intended. I think it may also be why Dave Jones chose to power his uCurrent from a button cell directly attached to his PCB: he wanted the power lines to be as short as possible.

Thanks again for posting the project!

[gohan]

@AWI do you think that logging reading to SD card could be a useful addition? (in case you want to monitor something for a longer time)