Is there a video on the proper usage of the Micro Current Gold?

[Roger2013]

Dave has a ton of videos so it must be out there, I just can't find it.  Is there a video on how to use the Micro current Gold device?   

Thanks

Roger

[suicidaleggroll]

A video?  Not that I'm aware of, it would be too short.

Connect the uCurrent in series with your device using the "Current Input" terminals, so current has to flow from the power source, into the "Current Input +" terminal, out of the "Current Input -" terminal, and then to your load (you could also put the uCurrent on the ground return line if you like), same way you would with any other ammeter.  Set the scale where you need it given your load's current draw, turn the uCurrent on, turn your power supply on, and use a DMM to measure the voltage across the "Voltage Output" terminals.  The relationship between voltage and current depends on the scale switch (1mV/mA, etc.).

[MLXXXp]

Also, be aware that the negative current input terminal is tied to the negative voltage output terminal. If you measure with an oscilloscope or other device that doesn't float the ground, instead of a meter, you may have to use standard isolation practices to prevent shorts through the ground lead.

[Turtle9er]

I just received my ucurrent and have been using it with an oscilloscope. From the videos of dave using the ucurrent, it seems he just hooks up the oscilloscope in parallel to a DMM. What do you mean by standard isolation methods? Is it bad to just hook up the probes directly to the ucurrent. This question is not directly related to original post, but I was wondering, what is the maximum voltage that you can feed into the ucurrent to measure? I want to measure the current from a medical stimulation device (muscles) that has a voltage of 150V (Grass S88 square pulse stimulator and the CCU1 constant current). Before I go hooking it up, I just want to make sure I don't blow anything up.

[xquercus]

Turtle9er,

Take a look at this video for why it's important to be aware of isolation of devices under test when using an oscilloscope: 

The key take away is that it requires some thinking to insure mains isn't shorted when testing devices connected to mains power.

[MLXXXp]

This question is not directly related to original post, but I was wondering, what is the maximum voltage that you can feed into the ucurrent to measure

The voltage that your circuit operates at doesn't matter for the µCurrent or other ammeters. The maximum current that flows through the µCurrent is what's important, because there's no protection against damage by overcurrent. (There's a thin section of trace on the circuit board designed to be a crude fuse, but it's just intended to prevent massive heat and burning of large areas of the circuit board, not necessarily to prevent damage to the electronics.)

I did some calculations of what the maximum safe current for each range might be. It's possible that higher currents may be safe but it depends on what protection circuitry is in the input op amp, which isn't specified in the datasheet. Here's my post about it:
https://www.eevblog.com/forum/crowd-funded-projects/current-gold-on-kickstarter/msg375819/#msg375819

I later reasoned that you could add protection diodes while powered off, to increase the some safe ranges. Here's that post:
https://www.eevblog.com/forum/crowd-funded-projects/current-gold-on-kickstarter/msg376311/#msg376311

Here's my implementation of adding protection diodes, plus other modifications I've made:
https://www.eevblog.com/forum/crowd-funded-projects/current-gold-on-kickstarter/msg448208/#msg448208

[igendel]

Hi, sorry for bringing this old thread back to life, but I just got my shiny new uCurrent Gold  and I don't want to ruin it...

My question is, let's say I'm measuring the current for an MCU while it's sleeping, on the nA scale. Suddenly the MCU wakes up by mistake and consumes 8mA. Will it make the uCurrent release magic smoke? Are there any safety tips to avoid this kind of trouble?

Thanks,

[suicidaleggroll]

Hi, sorry for bringing this old thread back to life, but I just got my shiny new uCurrent Gold  and I don't want to ruin it...

My question is, let's say I'm measuring the current for an MCU while it's sleeping, on the nA scale. Suddenly the MCU wakes up by mistake and consumes 8mA. Will it make the uCurrent release magic smoke? Are there any safety tips to avoid this kind of trouble?

Thanks,

You could run into problems on the higher scales, large currents could burn out the shunt resistor or cause other problems.  At low ranges and low currents it will just clip though, and the specific situation you called out could never happen anyway.  The nA range uses a 10k shunt resistor, 8mA across 10k would require an 80V drop, which you don't have.  You're probably running the MCU off of say 3.3V, and let's say it browns out at 3.0V.  That gives you 0.3V of margin, which at 10k means the MCU could only draw about 30uA before it browns itself out and reboots.

[igendel]

You could run into problems on the higher scales, large currents could burn out the shunt resistor or cause other problems.  At low ranges and low currents it will just clip though, and the specific situation you called out could never happen anyway.  The nA range uses a 10k shunt resistor, 8mA across 10k would require an 80V drop, which you don't have.  You're probably running the MCU off of say 3.3V, and let's say it browns out at 3.0V.  That gives you 0.3V of margin, which at 10k means the MCU could only draw about 30uA before it browns itself out and reboots.

Right, thanks. But in that case, how do I set up the measurement? The MCU will need the "high" current from power-up until it goes to sleep, and if I switch the scales on the uCurrent afterwards, the switch mechanism may cause a momentary disconnect, no? Or is the cap on the MCU power enough to take care of that?

P.S. If it wasn't painfully obvious, I'm no expert on these matters... about half the reason I got the uCurrent was to support Dave 

Edit: Ok, just found this answer from Dave... https://www.eevblog.com/forum/beginners/some-question-about-ucurrent/msg602122/#msg602122 so basically the uCurrent is not the best tool for my needs 

[Gyro]

You could try what I sugested the other day. I'm not sure how well it would work in practice and it would be heavily dependent on the 'mark-space' and duration of your active and standby periods...

https://www.eevblog.com/forum/testgear/use-current-gold-with-wide-current-range-50na-20ma/

[igendel]

[...] and it would be heavily dependent on the 'mark-space' and duration of your active and standby periods...

Yeah, I'm worried about that. Thanks for the idea though.

BTW like in some other comments I found, I get good and clear readings with a DMM, but mostly terrible noise on the scope. The circuit is just an AA battery and a 300K resistor, I tried regular measurement and differential... moved the setup around a bit to avoid interference from usual suspects... I do wish Dave will make a video explaining how to get crisp results like he did.

[mclemens1969]

Also, be aware that the negative current input terminal is tied to the negative voltage output terminal. If you measure with an oscilloscope or other device that doesn't float the ground, instead of a meter, you may have to use standard isolation practices to prevent shorts through the ground lead.

I smoked my uCurrent gold on the first use. I made some mistake along the lines of what you are describing. It did not release delicious smells.

[suicidaleggroll]

[...] and it would be heavily dependent on the 'mark-space' and duration of your active and standby periods...

Yeah, I'm worried about that. Thanks for the idea though.

BTW like in some other comments I found, I get good and clear readings with a DMM, but mostly terrible noise on the scope. The circuit is just an AA battery and a 300K resistor, I tried regular measurement and differential... moved the setup around a bit to avoid interference from usual suspects... I do wish Dave will make a video explaining how to get crisp results like he did.

That's about 4uA.  That's too much for the 1mV/nA scale, and on the 1mV/uA scale you'll only get 4mV.  Scopes really aren't designed for measuring single digit millivolt DC signals, I'm not surprised you're seeing a lot of noise.

[igendel]

That's about 4uA.  That's too much for the 1mV/nA scale, and on the 1mV/uA scale you'll only get 4mV.  Scopes really aren't designed for measuring single digit millivolt DC signals, I'm not surprised you're seeing a lot of noise.

Huh. That, I did not think of. 

I tried it now with a 4.7MOhm resistor on the 1mV/nA scale (expecting ~306mV Edit: because it's a 1.44V battery now  ), and while the reading is still a bit noisy, it's definitely much cleaner than what I got before. My forehead and walls thank you kindly!

I am surprised about my scope though. Being state-of-the-art (1991), I though it'll be more sensitive!