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Anyone interested in my Gadgeteer module to read very low currents accurately?


#1

I am currently busy designing a Gadgeteer module board for myself and can easily make a few extra’s if there are other people that would also be interested…

It is a module capable of making accurate measurements of extremely low currents (micro and nano-Ampere range). It contains some precision op-amps and even a 16 bit differential A/D in order to achieve this. The purpose of the module (in my case) would be to estimate expected battery life from a circuit running in low power mode from a small battery. But I think my module will have other uses as well such as measuring strain gauges, 4-20mA sensors, precision resistance measurements etc.

The first part of the circuit is based on a design that appeared in a magazine article which you can read online here: http://www.eevblog.com/projects/ucurrent/
I used the circuit found there but laid it out as a Gadgeteer module board and included a 16 bit differential A/D on the board as I needed better resolution that the 10 bits that standard Gadgeteer mainboards offer.

I think this module will be usefull to use in conjunction with the “Your PC becomes your gadgeteer mainboard” feature that GHI are inrocucing soon. (See https://www.ghielectronics.com/community/forum/topic?id=11713)

Since I am making some PCB’s for myself I thought I might as well make a few extra’s and offer them to other forum members as well at a cost of about $20. This post is merely to probe if there would be any interest in something like this from other members. I would then know how many additional boards and components to order. Once I get the first board assembled I will post some pictures and test results.

PS: Oh, and at the same time I also made myself a gadgeteer module that allows you to interface a 3V3 Gadgeteer mainboard with a 5V I2C chip. It consist for some N-Channel MOSFETS to do a bidirectional of the SDA and SCL lines and a resistor divider network to allow PIN 3 interrupt and a general input on pin 6 as well. I can also make some extras of this board if anyone is interested. It will cost about $10.


#2

Is it going to be something like this:

https://www.ghielectronics.com/community/forum/topic?id=8742


#3

@ Duke Nukem - I quickly looked at that thread, and it looks like it was quite an active one, Thanks for mentioning it… I did not read it before now.

However, my intention with this board is specifically to measure very small currents very accurately. The module will have three high tolerance current measuring resistors that will allow three ranges… milli-, micro- and nano-ampere. Because the measured signal will be amplified by op-amps, there is almost no voltage drop introduced by the very small shunt resistor. This is very important when measuring current drawn by battery backed up circuits where even a small voltage drop can influence the unit under test.

I also added terminals to output the amplified analogue signal so you can connect a normal multi meter or oscilloscope to it as well. And the I2C A/D operates at 5V supply to allow for the full range of 4.096V. It meant I had to add 3.3V to 5V interfacing on the SDA and SCL lines. But because of the differential nature of the A/D it means that the circuit can measure both positive and negative currents.