I have a UNO board, whose A1 pin is damaged, with only 3.9 ohm resistance to ground. while other pins >100ohm.
Now when powered on, the board is working as usual, except that the ATMega chip along is burning hot.
Is there any way to stop it from getting that hot, to use it a little bit longer before I can get a replacement ?
I assume you already tried writing different configuration and data values to it? In desperation?
just tried change mode. didn't help. nop haven't try any *write yet.
I do have a small promini board, but it doesn't have HREF pin, I need it to stop the readings from drifting when USB is plugged in or out. I also need the 3.3v pin to drive a extension module. I guess promini is no avail.
... What should I do now ?
What should I do now ?
Replace your processor chip. Unless you have another Arduion to program the new chip, get one with a boot loader already programmed in.
zcattacz:
I have a UNO board, whose A1 pin is damaged, with only 3.9 ohm resistance to ground. while other pins >100ohm.
Now when powered on, the board is working as usual, except that the ATMega chip along is burning hot.
Is there any way to stop it from getting that hot, to use it a little bit longer before I can get a replacement ?
The chip has latched up, its toast. Latch-up - Wikipedia
Thanks for the "death sentence", sounds like its hopeless now. m not good enough to solider surface mounted ICs...
To make sure my 2nd board is safe, I have some other questions...
My pressure gauge used to connect to this pin is of 4-20mA output, in fact it can go up to 25mA before out of range(the manual does mention it can handle 30% out of range), and down to <4mA (the reading is negative).
This is not the reason for the toasting. But just in case, is it normal for the other 4-20mA device to work like this?
I used to put a 4.7v zener diode in parallel to the resistor between A1 and GND, but the reading become non-linear, the calculated and actual gauge reading are different. If I remove the Zener. Its linear again. Is there any way to protect the pin without knowing the exact maximum current ? (to get higher resolution, one sure would like to get the maximum current close to 1023..., but it could happen that I dont know it for sure what the actual max can be, before try it out)
It's a surface mount Uno?
actually, this one:
Did you calculate the resistor value to keep the voltage below 5V? 25mA through 200 Ohms is 5V, so 200 Ohms would be the maximum value. (I'd still suggest a protection diode.)
The Zener should have worked as a protection device, but obviously you're not going to get the full 5V resolution.
[u]This Page[/u] shows another protection technique.
I did. A1 isn't burnt for that reason but something more dumb. the resistor value I calculated is 160ohm, for a 4.095V reference voltage. So a 150 ohm and 10ohm resistor is soldered together, with the joint leg left floating. during the next try that leg accidentally touched somewhere, m not quite sure where; then all of a sudden the readings go minus and never change back, and I realized something went wrong. 
But as a newbie, I was close to neglect that 25mA, just wonder if that is common for these 20-4mA sensors.
I supposed all 20-4mA sensor just output 20-4mA.
I tried with Zener on, but the reading I calculated from the 0~1023 raw value differs from the gauge reading. if I change the resistor value a little bit, it will match on certain range but deviate badly on the other range. very annoying. but with the Zener gone, it very easy to calibrate, I just need to back-calcuate the resistor value based on the gauge reading and raw value, and recalculate the equation factors based on that resistor value. Then it matches fairly well.
Since so many people suggest Zener diode for protection, did I do anything wrong ? I wonder why it didn't work in my case ?
What you saw was perfectly correct, a Zener is only useful to protect digital inputs not analogue ones.
You need to use a diode clamp from the input to the supply rail and also a series ever resistor to limit any overload current going down the clamp diodes.
zcattacz:
actually, this one.
Dead link.
However, the description cites a CH340G.
That is something that annoys me about the plethora of so-called "UNO R3" clones mendaciously advertised on eBay and other sites.
By definition many or most are not UNOs. A UNO is defined by using an ATmega16U2 (or 8U2 in the rev1 and rev2 boards). That is what UNO is. If it does not have an 8U2 or 16U2 then it is simply and undeniably not a UNO. Whether using a FT232 or CH340 or the preferred CP2102, it is essentially a Duemilanove and nothing more. The bootloader software - which may be UNO - is irrelevant to the hardware.
Dead link.
Worked for me:-
Maybe something is blocking it at your end.
However, it is a clone described as CH340G UNO R3 Development Module Board For Arduino but a price of £2.68 which might indicate the quality.
Grumpy_Mike:
Maybe something is blocking it at your end.
Sure is!
Access Denied
You don't have permission to access "http://www.banggood.com/ATmega328P-CH340G-UNO-R3-Development-Module-Board-For-Arduino-p-971919.html" on this server.Reference #18.455809d2.1439764426.238e049d
Blocked here as well
Go to http://www.banggood.com
Enter this in the search field.
ATmega328P-CH340G-UNO-R3-Development-Module-Board-For-Arduino-p-971919
Ah!
So the link quoted was missing the all-important directory "/buy/" in the middle!
Nope, that doesn't work either.
Apparently it is some psychopathic programming on the banggood server that only works if you are already on their web page.
Ah well, it's not as if I am going to buy anything from them anyway. I simply can't - their checkout system does not work for me. So bit by bit, their thoroughly antisocial programming is losing them business.
Karma.