miniLOG - a Precision Standalone Voltage Logger

[fenclu]

I'd like to introduce my latest project. It's a precise standalone voltage logger that saves the logged data to an SD card. I call it the miniLOG, because it's small and well, it logs stuff...

I have just finished the PCB and am about to be ordering prototype PCBs. Hopefully it will be on the market by the end of the year.

More details on my blog:  http://timecircuits.blogspot.com/2013/10/minilog-precision-standalone-voltage.html

I'd love to hear your feedback, either good or bad. It's supposed to be a kind of public research. I want to find out how many pepople would be willing to buy it, i.e. know the market.

Peace.

[MJLorton]

Great idea...if you could add current data logging as well at some stage you would have something special....not many of those about.
If you get it up and running I'd be more than happy to review to give you some exposure.

Cheers,
Martin.

[fenclu]

Well, pretty much all a user needs to do is measure the voltage across a shunt resistor and bingo - you've got a current logger. I'm ordering a prototype in a couple of weeks. But sure, I'd be happy to send you one.

[fenclu]

Here's an update on the miniLOG. I described the schematic on my blog: http://timecircuits.blogspot.com/2013/11/minilog-seires-part-2-circuit.html

I would be grateful if you could provide an outside opinion or possibly note any mistakes I've made in the schematic.

Also, I can't decide whether to use an SD card, or a microSD card, so please give me some advice on that.

[SeanB]

Few questions.

You need more capacitance on the battery side, add an extra capacitor on the battery input, 100uF 6.3V SMT caps will help as the battery ages or if you have a poor holder connection. Same on the main bus as well, extra decoupling will help.

What is the function of Q1, R12 and R13? They serve little function as far as I can see, unless you want to lose some voltage, where a smt inductor to filter the line a little would be a better bet, using almost any value of inductor with low DC resistance.

As to using SD or microSD, choice is yours as to how big a footprint you want to have on the board, best will probably to have a SD card footprint and place the microSD card footprint inside it so you can choose during assembly which adaptor you want to solder in.

[fenclu]

I got my prototype PCBs. I started talking to my Atmega chip and developing the software. I do however have a problem with the DC-DC converter. As you may know I used an AA battery with MCP1624/MCP1640 converter to boost the voltage to ~3.6V. The efficiency didn't turn out as expected and the entire circuit is drawing about 54mW (according to my crappy multimeter), not the expected 10mW. I'm thinking of just ditching the AA battery and using two CR2032s in parallel with some sort of protection diode. That would give me about 500mW in total. But the other problem is the diode dropout voltage, the voltage would be too low for the SD card...

Now something like a Li-Po battery would be nice but I think that might be a bit of an overkill. I would appreciate some help and suggestions.

Here are some photos of the prototype:

[MJLorton]

Great to see the progress.

I think Dacian (https://www.youtube.com/user/electrodacus) has a fair amount of experience in this area. He is also at the final stages of developing his Solar BMS for Lithium and Supercapacitors (https://www.youtube.com/watch?v=PSYo8Jkq8S0).
He might be able to help or give advice. Post directly to him on his channel as he is not on this forum.

Cheers,
Martin.