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Topic: ID Passive Components on Nano A3, A4 & A5 (Read 209 times) previous topic - next topic

eddycurr

Nov 27, 2020, 02:12 am Last Edit: Nov 27, 2020, 08:07 am by Coding Badly
I am attaching an image of a Nano in hopes that someone can identify the green components attached to the A3, A4 & A5 pins.  At least one of the pins is an input for an analog voltage signal from a sensor.

The objects have a shape similar to that of ceramic disk capacitors, but they are "Gloss Green" instead of the "Flat Tan" colour I am familiar with for small disk capacitors.

Someone suggested that they look like Radial Leaded Metal Oxide Varistors (MOV).  I agree that they have a similar physical appearance, but the MOVs I can find on line are either blue or red in colour.





gilshultz

Those devices are not normally on the Nano. It appears like you are reverse engineering a project. I would guess they are MOVs See what the other end is connected to, that will give you a hint. If it works measure the voltages etc.
This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil

Wawa

A MOV directly on a pin would have been a designer mistake.
No protection at all when the Arduino is off, and it's knee point would not be sharp enough to protect when on.
Leo..

eddycurr


Those devices are not normally on the Nano. It appears like you are reverse engineering a project. I would guess they are MOVs See what the other end is connected to, that will give you a hint. If it works measure the voltages etc.
I only have an image, no board in hand.

As mentioned, at least one of the green radial leaded objects passes input received from a sensor (a voltage divider circuit comprised of a variable and a fixed resistor) to one of the Nano's 0-5VDC ADC channels.  The voltage divider is powered by the Nano's +5V pin.

Also.  There is a DC-DC Boost Converter on the board (5V to +/- 15V) and an unidentified 8-DIP IC that may be an instrument amplifier included to provide gain for the signal output from the sensor.

eddycurr

A MOV directly on a pin would have been a designer mistake.
No protection at all when the Arduino is off, and it's knee point would not be sharp enough to protect when on.
Leo..
"No protection at all when the Arduino is off, ..."

Is this remark based on an assumption that ESD protection was the objective for inclusion of the green components, if they are MOVs?

Instead of ESD, could the purpose be protection for the Nano's ADC channel from signal amplification exceeding 5 VDC? 

Wawa

What else should a MOV on a pin be used for.
Over-voltage protection is the only thing I can think off.

Generally speaking, a MOV, or a zener, or a TVS diode can't fully protect the pin. Only clamping diodes can.
Don't forget that max pin voltage is not 5volt. It's VCC + 0.5volt (and GND - 0.5volt).
When the Arduino is off, VCC is zero volt.
Leo..

eddycurr

#6
Nov 27, 2020, 09:05 am Last Edit: Nov 27, 2020, 09:13 am by eddycurr
What else should a MOV on a pin be used for.
Over-voltage protection is the only thing I can think off.

Generally speaking, a MOV, or a zener, or a TVS diode can't fully protect the pin. Only clamping diodes can.
Don't forget that max pin voltage is not 5volt. It's VCC + 0.5volt (and GND - 0.5volt).
When the Arduino is off, VCC is zero volt.
Leo..
Yes, MOV on a pin for the purpose of over-voltage protection.

The distinction I was aiming for is that perhaps the design purpose was a narrower, more modest objective of protection from a bit too much amplification while operating.  As opposed to protection from the higher voltage arising from static discharge or a bolt of lightening.

(To put things in perspective - this morning I hadn't used "varistor" in a sentence before.)

I have an interest in figuring out what the green objects are.  I know capacitors are used on Arduino analog pins for multiple purposes, but these objects didn't look like capacitors to me.

At the time of posting, I hadn't observed instances of green MOVs, only blue and red.  That created doubt as to whether the objects in the photo were MOVs.  In the interim, I discovered examples of green MOVs on Ali-B - these look VERY similar to the objects in the photo.

So maybe the objects ARE MOVs.  This leaves the questions raised here about suitability of MOVs in that application to be answered.  I suppose the path forward is to piece the rest of the components I have recognized together into a working circuit, see what I observe at those pins and then accommodate as appropriate.

Thank you for your insights regarding alternative means of dealing with over-voltage.  This will be helpful if o-v p turns out to be a requirement.


Paul__B

Actually a picture would be useful.

I am afraid a thumbnail is entirely useless!

I only have an image, no board in hand.
Best forget it for now then.  :smiley-lol:

TomGeorge

Hi,
What is the project that this image is off?
What does it do and what are you trying to do?

Tells us the bigger picture and stop concentrating on the "green objects", telling us what system you are looking at will help make an informed reply.

Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

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