Author Topic: Current Ranger produces a 0.45V Voltage Drop when Off.  (Read 643 times)

flashbac

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Current Ranger produces a 0.45V Voltage Drop when Off.
« on: February 18, 2019, 03:11:05 PM »
Hello everyone.

I have an Atmega328P on a breadboard with a minimal install of VCC, GND and AREF (5 pins total). I'm supplying a constant 3.3V and my DMM does in fact read 3.3V on the breadboard +/- rails. When I hook up the Current Ranger and turn it ON, my DMM still reads 3.3V on the breadboard +/- rails, however, when the current ranger is OFF the DMM reads 2.85V.

I have tried the same test above with 3.7 Li-on batteries outputting 4.17V and I got the same loss, -0.45V when the Current Ranger is OFF.

I also tried with a 5V power supply and got the same results.

Note: I'm not sure if this is related but, when I disconnect the GND pins from the Atmega328P, the problem goes away.

Any thoughts on what might be going on here?

Thanks!

Lenir


Felix

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Re: Current Ranger produces a 0.45V Voltage Drop when Off.
« Reply #1 on: February 18, 2019, 09:37:27 PM »
If it's off, and your load is still going through it, the switches are going to route the current through the nA stage, which I think explains the large drop you're seeing.

But I'm not totally following why is the CR off?
Wouldn't you normally use it when it's ON?

flashbac

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Re: Current Ranger produces a 0.45V Voltage Drop when Off.
« Reply #2 on: February 18, 2019, 11:51:38 PM »
The problem is when the auto-power-off kicks in while I'm working on my project everything starts going nuts due to the voltage drop, then I start to troubleshoot and a few minutes later I go "oh yeah, the CR shut off"... It would be nice if I could leave my project running without having to worry about the CR being on/off. Also my current project involves the atmega328p and an Xbee3, both running at 3.3V so the voltage drop is even greater when both are running. It would be nice to be able to leave the project running for extended periods while the CR is inline, that way I can just turn it on/off as needed, and if I forget about it then the auto-power-off won't mess anything up.

Maybe for the next CR revision, when off, it should be a passive device with no voltage/current loss :) Is there a way to have the CR run the current through the mA stage when off to avoid this? Is this something software configurable?

Uncle Buzz

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Re: Current Ranger produces a 0.45V Voltage Drop when Off.
« Reply #3 on: February 19, 2019, 03:39:15 AM »
Maybe a modification in the firmware to avoid auto-power-off when there's some current through the CR ? only auto-power-off the CR when there no current, when you don't use it ? An option enable by serial on USB so there's no change for people who don't need it ?

flashbac

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Re: Current Ranger produces a 0.45V Voltage Drop when Off.
« Reply #4 on: February 19, 2019, 08:58:17 AM »
Good ideas, but those disables auto-power-off, we would be losing that feature and it would drain the battery if the project requires running for extended periods. It would be better to just be a passive device or for the current to go thru the mA stage when the CR is off, that way we get the best of both worlds :) But if that cannot be done, then your ideas would be a very good alternative.

Uncle Buzz

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Re: Current Ranger produces a 0.45V Voltage Drop when Off.
« Reply #5 on: February 19, 2019, 09:57:09 AM »
use a jumper or something else to short the CR when you don't need it, it will measure almost 0 current and will auto shut off without droping voltage, and will stay on if there is no jumper and some current (with the suggested firmware modification).

Felix

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Re: Current Ranger produces a 0.45V Voltage Drop when Off.
« Reply #6 on: February 19, 2019, 10:48:17 AM »
The problem is when the auto-power-off kicks in while I'm working on my project everything starts going nuts due to the voltage drop, then I start to troubleshoot and a few minutes later I go "oh yeah, the CR shut off"... It would be nice if I could leave my project running without having to worry about the CR being on/off. Also my current project involves the atmega328p and an Xbee3, both running at 3.3V so the voltage drop is even greater when both are running. It would be nice to be able to leave the project running for extended periods while the CR is inline, that way I can just turn it on/off as needed, and if I forget about it then the auto-power-off won't mess anything up.

Maybe for the next CR revision, when off, it should be a passive device with no voltage/current loss :) Is there a way to have the CR run the current through the mA stage when off to avoid this? Is this something software configurable?
flashbac,

From what I understand you have this use case:
- you need to make sure the device runs and the CR stays ON (for logging purposes I assume)
- you also need to be able to forget about it, and in this case it should turn off to save battery life
- and if it does turn off, the DUT has to be able to keep going, although at that point having the CR connected is not useful, it doesn't do anything when it's off

Can this be configured in software? Yes, but only when the CR is ON. There is no device that does something when it's OFF :)
I will explore a way to make it go through mA instead.

flashbac

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Re: Current Ranger produces a 0.45V Voltage Drop when Off.
« Reply #7 on: February 19, 2019, 04:05:29 PM »
flashbac,

From what I understand you have this use case:
- you need to make sure the device runs and the CR stays ON (for logging purposes I assume)
- you also need to be able to forget about it, and in this case it should turn off to save battery life
- and if it does turn off, the DUT has to be able to keep going, although at that point having the CR connected is not useful, it doesn't do anything when it's off

Can this be configured in software? Yes, but only when the CR is ON. There is no device that does something when it's OFF :)
I will explore a way to make it go through mA instead.

Felix,
Correct, I want the DUT to continue functioning properly whether the CR is on or off. I'll turn on the CR when I need it, and turn it off when I don't need it or when I forget about it (via auto-power-off). I won't have to worry about plugging or unplugging the CR when in use or not in use.

Thanks!

alexsh1

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Re: Current Ranger produces a 0.45V Voltage Drop when Off.
« Reply #8 on: February 23, 2019, 01:15:52 PM »
Felix,
Correct, I want the DUT to continue functioning properly whether the CR is on or off. I'll turn on the CR when I need it, and turn it off when I don't need it or when I forget about it (via auto-power-off). I won't have to worry about plugging or unplugging the CR when in use or not in use.

Thanks!

The quickest option is to change auto-power-off.
Either disable it for now or increase it to suit yourself.