New Improved DIY Milliohm Meter V2.0

RE: New Improved DIY Milliohm Meter V2.0

John_K — Wed, 01 May 2024 01:48:41 GMT

I would love the opportunity to build one of these units. Have you made any alterations since the last posting? I am in Australia & just starting out on my electronics adventure, as I am now retired. Do you have the base circuit boards for purchase, or would I need to get it made myself? Look forward to your reply.

RE: New Improved DIY Milliohm Meter V2.0

dubbie — Wed, 23 Sep 2020 12:11:55 GMT

Frank,

A nice PCB. One dayt, probably in the far distant future, I too will be able to make PCBs like this.

Dubbie

RE: New Improved DIY Milliohm Meter V2.0

fmilburn — Wed, 23 Sep 2020 05:03:59 GMT

I've added a new sheet to the schematic above with an ADC and microcontroller:

[View:/resized-image/__size/620x429/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-7bb6ad62-84a3-412c-8627-5c1dc1277c3b/3225.contentimage_5F00_192338.png:620:429]

Below is the revised board:

[View:/resized-image/__size/620x644/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-7bb6ad62-84a3-412c-8627-5c1dc1277c3b/0172.contentimage_5F00_192339.jpg:620:644]

I'm currently doing a RoadTest that came with two Infineon XMC 2Go boards and I decided to use one for this experimental version of the Milliohm Meter. I have been looking for a small and inexpensive ARM chip to replace the MSP430 that I have mostly using up until now and the XMC 2Go has a M0 ARM microcontroller and is tiny enough to fit on the PCB and inside the enclosure. I haven't made a decision on the microcontroller but any microcontroller could work and I can use flying leads if needed.

The ADC to the right of it is the MCP3421 which is the same ADC in the little voltage meter that Shabaz recommended and works so well.

I tried putting in a more general prototyping area but KiCad was giving me problems this evening. For a change, I think it might be KiCad and not me and noticed I am using quite an old version so will update. I fully plan to spin another board and this should be good enough to validate the changes made so far. If the microcontroller and ADC work then can add reed switches? to auto-range, a new display, and power management.

RE: New Improved DIY Milliohm Meter V2.0

Andrew J — Tue, 22 Sep 2020 18:15:52 GMT

Excellent work. I Have this on my list of things to make Frank, but not right now so keep tinkering. I like the idea of battery driven and MCU control.

RE: New Improved DIY Milliohm Meter V2.0

genebren — Mon, 21 Sep 2020 19:09:58 GMT

Looking very good!

If you are talking about batteries and battery indicator, why not consider a Li-ion solution with a built in recharging circuit. I have a clean little charger/boost circuit that you could add in. It also includes a microcontrolller (ATmega328PB) that has some spare pins that could address your future growth areas.

Let me know if you have any questions or if you need any assistance.

RE: New Improved DIY Milliohm Meter V2.0

shabaz — Mon, 21 Sep 2020 15:20:26 GMT

Hi Frank,

That looks nice! The different areas on the board (power, current source, amplifier, processor) make it easy for people to tweak and enhance the design I think. Also, it seems a great idea to have the single 28-way connector, because it could reduce wiring, if there is a front panel PCB in future.

Regarding the USB connector, I have lots of DC barrel plug supplies so I prefer socket for those, but equally others may prefer USB power, it's hard to know what is more popular.

I was thinking, maybe the blank area on the PCB could be populated with 0.1" spaced pads, and perhaps even a land pattern for the ADC you wish to use (maybe the same one as in the panel meter, which is MCP3421, since it worked well), so you have space to experiment.

If you're ready to send off your PCB though maybe it's not worth the bother.

I only mention it because by coincidence I just finished a PCB design to fit a Hammond case too (love those because of the front panel), and I had some space to fill too.

If you're looking for more feature creep, maybe the power LED could be replaced with a low-battery indicator. I'll write up an example implementation in a short blog post tonight, in case you wish to use it, but if you're planning on having a microcontroller eventually then low-bat functionality is better implemented in the microcontroller.