Products > Test Equipment

Qoitech Otii

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cgroen:

--- Quote from: Commander_Spock on January 29, 2019, 05:34:28 pm ---in my understanding you have to pay every year their subscription to get their premium solution that include scripting and api.... except if we buy one and code something we open source via github

--- End quote ---

I fear that  |O
There is no way on earth (or any other place in the universe) that we are going to buy test equipment that has a subscription model. Period.
I wish Saleae would do something like this, their analyzer stuff screams for something like this, couple it together with the logic analyzer so you have the power consumption etc sync'ed to the rest of the signals (I have a Pro16 and ABSOLUTELY love it)

Commander_Spock:
we have several lowcost 8 channels chinese logic analyzer but we bought recently a dslogic plus that is pretty good and is working well with sigrok
anyway our i2c or spi bus are so slow that we do not need expensive logic analyzer

for spi/i2c we bought some nice and cheap tool on crowdsupply... received and use the spi and wait for march their i2c... more at https://www.crowdsupply.com/excamera 

andyturk:
I do own an Otii/Arc and use it frequently for projects (with batteries) where power management is important.

Pros:

1. The application is pretty handy. It's easy to just have the thing running all the time collecting data and then zoom into something interesting. When you're able to see the power consumption of your board constantly, it helps build a sense of what's going on. Sending screen grabs of the app is a good way to communicate with co-workers.

2. Physically, it's well built, small, and easy to carry. I've travelled with the Otii a couple of times because I didn't have room to bring another power supply. As long as you can get by with low voltage and not a lot of current, it's fine.

3. It's pretty accurate. I can't say exactly, because I don't have another instrument like it, but it's certainly good enough for making sure you're going into sleep mode and verifying that your battery charger is configured correctly.

Cons:

1. Not cheap. I paid something like $600 USD for the device without the subscription B.S. FWIW, I loaned it to another engineer friend and he ended up buying one too for his very low-power project.

2. Very limited capability as a power supply. It's great that the thing can supply power from only a USB connection, but that limits the voltage to (can't remember exactly) 4 volts or so. Not a whole lot of current either, but probably enough if you're only charging 200mAh batteries. You can plug in a 9V brick to supply more than 4V, but the brick is annoying and it's still a very low output. The device would be a lot more useful if it could pull more than 500mA from USB and boost/buck it to a larger range of voltages. And when the external power brick is attached, it should clearly be able to provide more power than it does.

3. It's got a stupid micro-USB receptacle. There was plenty of room for a larger USB B type receptacle that would be more durable.

Commander_Spock:
found maybe another solution using an high side current monitor using chips like ina219 or ina3221 and bought two small board using these chips from aliexpress in order to test (yes we will have to wait due to chinese new year as all stop in china for 2 weeks)
unsure if precision will be good enough but these chips measure current and send result via i2c bus. if we use a cheap  esp32 we could get result via wifi or bluetooth and it is then easy to integrate all in our automatic testbed
still unconvinced that a 20 usd solution would produce same result/precision than qoitec this is why i do not rule out using qoitec at some point in the future but clearly we will not buy their subscription based premium solution

for more on this possible solution take a look at https://tech.scargill.net/ina3221-triple-voltage-current-monitor/  and http://henrysbench.capnfatz.com/henrys-bench/arduino-current-measurements/ina219-arduino-current-sensor-voltmeter-tutorial-quick-start/

jeremy:
As far as I know, there are 3 ways to solve this problem:

1. regulator with remote sense => Current sense resistor => high gain differential amplifier => high resolution ADC (this is what this device seems to use). Depending on how you set up your remote sense, you can hide the voltage drop across the current sense resistor. Downside is that you need some sort of range switching to take place, and you can lose resolution on different ranges (aka limited dynamic range).

2. Energy metering by pumping "packets" of charge into a storage device and measuring how many packets you send. I haven't seen this in a real device, but it may exist?

3. Use a calibrated mosfet with a known V/I curve as a variable current sense resistor, but otherwise similar to option 1. I imagine it is quite complicated to get the feedback loop right, but it means that you can use a lower resolution ADC and as such a faster sample rate. I think the N6781A uses this approach with an 18 bit ADC @ 200khz to achieve an "effective" dynamic range of 28 bits (or so they claim). To be honest, I can't test it, because on paper this device is probably the most accurate in this type of instrument that I own. I suspect that the N6781A does low side current sensing so that mosfets are available with the lowest Rdson possible. One thing I can tell you is that for a 6V/1A supply, it uses some serious cooling in the various backplanes, so it must be generating a lot of heat.

Also, a lot of work needs to go into leakage. You're talking <1uA in some of these use cases and you need guard traces, shielding etc to minimise leakage. Note that in the photos of this device, the current sense region has lots of large holes around it to presumably reduce leakage and to reduce thermal coupling to the regulator and rest of the main PCB.

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