Changed all holes to non-plated and looked around for cheapest PCB options!

I just realized that my mounting holes for the OLED were plated for some reason which was totally unnecessary.

Additionally, I looked at JLCPCB, PCBWAY, and OSHPARK, and found that OSHPARK had the cheapest PCB (although it will take like 2-3 weeks to arrive, hope the PCB doesn’t have issues because I won’t have time to iterate before the deadline).

Last thing I did was I found a entry in the BOM that was accidently left there from an earlier revision (some screw terminals) and removed them.

Why is the documentation so bad?

I just can’t seem to find any documentation or clear way to wake up from a GPIO pin going HIGH! I’ll have to do some more digging to figure it out.

Besides that, I worked on the sensor and OLED code and its mostly finished. I think that I’m making some pretty good progress. Just got to figure out how to fix sleep.

Also I updated my PCB a bit because I didn’t realize it’s not a good idea to put two BJT transistors in parallel for different signals and I just used another control pin on my nrf52840. That did mean adding two more SMD resistors but they are pretty small and didn’t take up any additional space.

Started the code for the handheld hall effect current sensor!

Just initialized the code and got platformio working!

Finished the screw holes!

I used a nut retainer and one screw to compress the two halves of the case together with the PCB inside. I made sure to put the correct tolerances so the PCB will be the first thing compressed against. I’m using 4 M2 hex screws.

There isn’t much more stuff I can do until my funding (hopefully) gets approved and I can get the PCB and components. Then I can put everything together and fix any issues that come up.

For now, I’ll continue working on polishing it and double-checking my cad and PCB to make sure everything should work.

Case and calibration procedure starting to take shape!

I’ve cadded the top of the case to fit into the bottom! You can see how there are there are two holes on the top for the OLED screen and the on/off button and a slot in the front for the sensor portion to come out. The current size is 32mm x 36mm x 88 mm. It’s a bit larger than I imagined it, but still easily handheld. I’m still working on the screw holes and nut retainers and polishing the case. I’m sure there will also be plenty more changes when I get the parts and find out how they all fit together.

Additionally, I’ve figured out how to easily calibrate the sensor. So basically, you first calibrate at 0 amps and turn the reference screw until the output is 0. Then you put a known current and tune the sensitivity screw until the read current is the known current (or the known current times a certain multiplier).

Finished the PCB design!

I finished routing everything and checked to make sure it looks okay. I also finished my BOM and have a pretty good idea on how the rest of the project will go. I think I’ll try to submit for funding today and I’ll continue working on the casing design too.

I’m also struggling to keep the size small enough to be comfortably handheld because the way its looking right now it looks like it might be around 4cmx4cmx10cm and i want to try to get that down to 3cmx3cmx3cm.

Just discovered trimmer potentiometers!

I can’t believe that I wanted to swap out through hole resistors before! Now, I’ll be using two trimmer potentiometers, one to change the sensitivity of the hall effect current sensor and the other to change the reference voltage.
The schematic shown here still has a few issues (VR2 has too wide of a range). I’ll also need to redesign my PCB and this time I’ll be using all SMD resistors. I don’t trust my hand soldering skills enough to use 0402 sizes, so I’ll be using the larger 1206 footprint.
Other changes include changing the op amp configuration to an instrumentation amplifier, using a new op amp chip with 4 op amps (although I’m only using 3), and adding another transistor turn of ALL the power (except to the microcontroller) while the sensor is off.

I changed the op amp!

I realized today that I was using a 50 year old op amp! 50 years?! I should be able to get a op amp that’s cheap, faster, has lower noise, and is rail to rail! I found a new op amp, the COS8092SR, which features:

• 300 MHz gain bandwidth product
• 9nV/√Hz input voltage noise density
• 200 V / us slew rate
• Almost the exact same package (actually smaller)
• Rail to rail operation
• And just 30 cents apiece!

I’ve updated that and I’ve finished up my BOM.

Just started my physical CAD for the casing!

I started cadding the casing for my hall effect current sensor! The hardest thing about it was making sure the battery could fit while fitting the mounting screws. It was a pretty close fit but the screws shouldn’t need to bear much load so hopefully they don’t break the 3d print. I spent around 20 minutes trying to fit the screw holes in a way that looked okay and shouldn’t intersect with anything on the PCB.

Then I realized that I wanted the top part to interlock with the bottom, so I added a small slot around and thickened the walls so the slot could fit. I also had to make sure to leave space for the hall effect sensing circuit could come out.

I’m trying to keep this as small as possible that way this can be some kind of handheld device.

Next time, I’ll continue to work on the top part of the container and polish it up.

I almost fried my seeed studio microcontroller!

Well, kind of. I forgot to put a resistor divider between my 5v op amp output and my 3.3v seeed studio nRF52840 microcontroller. I’ve now added two SMD resistors to the underside of the PCB. It’s getting really tight in the pcb (just look at the traces), but I really don’t want to make it any bigger.
I forgot to say from last time, but I also added a on off button (how did i forget that?), some mounting holes, and a BJT transistor to actually turn off parts of the circuit when in sleep. I think I will start modeling the case for it no because most of the elements in the PCB are done.

Big changes to the hall effect current sensor! I’ve added a microcontroller and screen to display measured values directly! I’m using a Seeed Studio nrf52840 microcontroller. I also decided to add a battery to the back to make it a standalone sensor. I’m not actualy sure if there are lipo batteries small enough to fit and not get in the way of the screws, etc so I might have to use coin batteries. There shouldn’t be much more to add to the PCB I think so I will probably start working on the casing, which I’ll 3d print.

I’ve decided to switch over to a smaller surface mount op-amp. It has higher gain-bandwidth product, lower noise, higher slew rate, and a smaller footprint. I’m working on miniaturizing the circuit so it is smaller and easier to use. I still want to use through hole resistors so the gain and reference voltages are easier to tune.

Working on the PCB design for my hall effect current sensor!