Pi Pico Power Meter

Project Logs

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Fully isolated improvement
Per-Simon Saal • 03/16/2024 at 10:23 • 0 comments
While I was measuring the consumption of other projects I realised that I really need to take care of the wiring. Especially the GND connection. Eventually I destroyed one chip through misconnection.

That led me to the point that the device needs to be isolated. Only this way it is safe to use two of them to perform efficiancy measurements.

There are two ways of isolating the PPPM:
1. Isolating the input USB connection.
2. Isolating the onboard power and I2C.
I decided to to the latter because I have no access to the USB-C connection on my PCB.

After a brief search online I found the I2C isolating chip: ISO1641B from TI. It is very easy to use and needs only two external bypass capacitors. The Clock is transmitted unidirectional and the data is bidirectional.

For the power isolation is was a bit harder to find a good space saving solution. Usually there are chips that drive a discrete transformer and on the secondary side you need a LDO to regulate the correct voltage. All that leads to a high BOM count and needed space.

But I was lucky and discovered that TI is coming up with a highly integrated, space saving and cheap chip that does all of this! It is the UCC33420.

To make space for the two additional chips I moved some components around. The shunt resistor and a couple of resistors moved to the back side of the PCB. Now they can be changed without removing the OLED. I should have done this before!

The layout is done and the PCBs are ordered! Now let's wait for it and that the transformer chip becomes public available.

I disabled the THT components to see below the OLED display.
USB Power Measurement
Per-Simon Saal • 04/21/2023 at 13:42 • 0 comments

Some Code adjustments made it possible to track the charging power of my old Nexus 10 tablet.

With a button push the data are logged to a csv file. Another press will stop the logging.

For a decade I was wondering why the charge performance is bad. I can see that the charging current is variing all the time up and down.

After I took the photo I added the ground wire to get the voltage.
Housing ref 2
Per-Simon Saal • 03/19/2023 at 18:37 • 0 comments

I have reworked the 3D printable housing.
Just have a look yourself:
It came out a bit ugly due to a dirty printer bed...
You can find the .step data on my github repo.
Next Revision - nice features
Per-Simon Saal • 03/06/2023 at 16:24 • 0 comments

During testing the Power Meter I discovered some minor things I wish I had done different.

First, and most important I wanted to get rid of the pin headers to solder the MCU module. This only adds costs and is unconvenient.
I also added some TVS diodes for the measurement inputs and a mouse bite divideable protoboard for the controller headers.

Before, I got a message from PCBway that they would like to sponsor the next revision of PCBs.

That's a really nice circumstance and I used the offer for new PCBs. It was the first time I ordered there.
The PCBs are really nice - like I expected. The HASL finish looks very even and the silkscreen is very clear and sharp. One thing I did not expect was the outer milling of the boards. Often the outline is not that important than the dimensions on top of the FR4. But nothing caught my eye that was not finished perfectly and all the dimensions are bang on!
All in all a very good job! Thank you very much!
Home sweet housing
Per-Simon Saal • 02/22/2023 at 15:51 • 0 comments

I finally got the printed housing from my friend.
It looks already quite good but some dimensions are not correct. I also need to think about the different height of the components: headers, button, display.
Let's see what I will think of...
Housing tadaa
Per-Simon Saal • 02/11/2023 at 12:05 • 0 comments

After some trouble designing a 3D printable housing I have a first prototype.
I've ordered the 4 parts from a friend who has a 3D printer.
This design I need to glue. Don't know if it is the best approach. Let's see when I have the parts in my hands.
But have a view on the renderings I've got from Fusion360:
It becomes real
Per-Simon Saal • 02/05/2023 at 11:40 • 0 comments

My PCB order was deliverd yesterday.
After a bit of soldering and testing - everything works!
It feels really good to have some working hardware in the hands.
With the battery and the two resistors I made a quick energy measurement of this disposable rechargeable Li-Ion battery from a vape pen.
It should contain 2.025Wh. With my measurement I calculated 1.92Wh. That is quite good!
I don't want to interrupt you...
Per-Simon Saal • 02/03/2023 at 15:32 • 0 comments
... but actually I do!

I switched the push button mode from polling to interrupt mode.

Now it is possible to log the data as .csv file on the onboard flash. Does anybody now what happens when the file exceeds the available space?

Furthermore, I created a github repo to share my HW and SW files with you.

Additional ideas in my mind:
- Make a daughterboard with more switches
- Create a menu to make settings
  - Logging: save single data set, save continous, ...
  - Set voltage and current resolution
  - Measurement mode
  - Timings
GUI Ahoi!
Per-Simon Saal • 01/31/2023 at 20:51 • 0 comments

It was time for a nice GUI.
Well a really nice GUI on 2cm² is hard to realize but at least I could make everything good readable.
Due to the lack of different fonts and sizes in the default micropython library I searched for something easy to implement.
And I found it! Peter Hinch has written a really nice library in micropython hat is based on the official drivers for the frame buffer and the SSD1306 OLED display I use.
With some modifications in the code it just runs perfectly on my Pi Pico!
So, if you need a good GUI library that offers some fonts in different sizes, nice widgeds and is portable to many microcontrollers check his repo!
Now, here are some pictures of my 'pages'. With a push button it is possible to move from one 'page' to another.
Custom PCB
Per-Simon Saal • 01/28/2023 at 15:40 • 0 comments

A custom PCB is a nice feature to move from the protoboard to reliable connections.

My goal is to make a nice small and space saving PCB. Thus, I will not just plug breakout boards to their headers on the PCB but will solder them directly to the PCB.

With one exeption: The RP2040. I don't want to face any trouble doing the connections on my PCB - Controller - Crystal - Flash. I would like to take an off the shelf part - like the Pi Pico. But as already meantioned it is to large for my application.

My research led me to the RP2050 Femto which is a pretty nice approach to shrink the size. With a form factor of only 11x11mm it is just bearly bigger than the Controller itself. But unfortunately I coundn't find it to buy.

I heard also of the RP2040 stamp which is also a very nice board because it contains some extra features the Pico doesn't have. But 25x25mm is an unlikely formfactor for my project.

Next, coincidental I came across the RP2040 Nano which has a formfactor that suits my needs! Yes, not all pins are easy accessible but I don't need all the pins. It contains also some extra features like an reset button, a Neopixel LED and is future proof with a USB-C connector.

That's the board I take!

Next the PCB design wich is quite easy. I added another user button and two user LEDs.
To make use of the (so far) unused pins I added two rows of female headers. Their distance is in multiple of 2.54mm to easy stack-up another PCB.

The INA219 chip is addressable with all 16 addresses. One just need to change the position of the pull-up resistor.
In default assembly only one 2512 sized 100mOhm shunt is populated, but with higher currents in mind I added a second unpopulated footprint in parallel.

The screw terminal is the biggest component but also very robust and can hold wires up to 2.5mm².

Everything important is labeled in the silkscreen.

The PCB has a size of 75x30mm.

All files will be available on my github when everything is confirmed.

Now I might need a 3D printable housing...