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Author Topic: Range switching speed  (Read 1080 times)

mayor

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Range switching speed
« on: March 29, 2021, 07:58:28 PM »
Hello,

just getting started with the CurrentRanger. Pretty cool so far, but I am having an issue testing a TI CC1312 board which transmits to a 15.4 gateway every few minutes. Power is currently provided by a CR2032 cell.

When auto-ranging is enabled, I notice that the transmission often fails (as current draw spikes very suddenly).

Any pointers what could be done to ensure a faster/smoother transition to avoid brownouts?

(ah, I just spotted this in the docs). Can a pic be posted of exactly where and what orientation the diode is supposed to be?
« Last Edit: March 29, 2021, 08:17:25 PM by mayor »
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Felix

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Re: Range switching speed
« Reply #1 on: March 29, 2021, 09:18:24 PM »
Quote
Add an external diode across the input terminals (from positive > to > negative) – this starts conducting at the diode forward voltage (~0.7V) when there is too large of a drop across the current range shunt. This way, if your MCU can handle a 0.7V drop, then it should not brownout until the proper range is switched. Be aware that the diode can have some leakage, but generally you should still get a fairly accurate reading at the output.

= Anode at CR INPUT+, cathode at CR INPUT-.
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mayor

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Re: Range switching speed
« Reply #2 on: March 30, 2021, 03:49:14 PM »
Hello,

is it possible to somehow calibrate the diode out? Where I was reading an average of roughly 100 nA, I am now reading 111.
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mayor

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Re: Range switching speed
« Reply #3 on: March 30, 2021, 04:20:54 PM »
Meh- the transmissions still fail even with the diode.

What part of the code can be modified to speed up the range switch?
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Felix

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Re: Range switching speed
« Reply #4 on: March 30, 2021, 06:01:18 PM »
Did you try a Schottky?

How about temporarily using a different PSU that delivers the same voltage and perhaps more current capability than a cell coin (so internal resistance). At least that broadens your testing capability and helps you narrow down the brownout.

It has to do with how fast it samples the ADC. Speeding up is a little more tricky and involved multiple things. I would not recommend going and modifying the code unless you are somewhat experienced with the SAMD, in which case I am sure you could find that in the code.
« Last Edit: March 30, 2021, 06:04:34 PM by Felix »
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mayor

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Re: Range switching speed
« Reply #5 on: March 30, 2021, 06:57:52 PM »
I'll try both approaches and let you know, thanks.
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mayor

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Re: Range switching speed
« Reply #6 on: April 02, 2021, 12:02:19 PM »
Schottky: no joy.

Power supply seems to have done the trick. Guess I'll have to use a battery-powered laptop for measurements over time.

Thanks!
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