Hello,
I am trying to do a simple voltage divider project with an Arduino uno. When I put together the circuit with a breadboard, it works fine. Then I move the resisters to a project board and solder the parts together and it no longer works. The number reported by the voltage divider is approximately half of what it was before I soldered the parts. I have destroyed three project boards and resister sets.
Could I be damaging the resisters with the soldering heat?
Other ideas?
Please post photos.
Hi,
Welcome to the forum.
Please read the post at the start of any forum , entitled "How to use this Forum".
OR
http://forum.arduino.cc/index.php/topic,148850.0.html.
Then look down to item #7 about how to post your code.
It will be formatted in a scrolling window that makes it easier to read.
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Thanks.. Tom... 
HenryJD:
Hello,
I am trying to do a simple voltage divider project with an Arduino uno. When I put together the circuit with a breadboard, it works fine. Then I move the resisters to a project board and solder the parts together and it no longer works. The number reported by the voltage divider is approximately half of what it was before I soldered the parts. I have destroyed three project boards and resister sets.
Clearly you've made an error - have you thought to measure the resistors in the circuit you have made with a meter?
Could I be damaging the resisters with the soldering heat?
Very very unlikely, they are made from metal and ceramic and need to glow red before burning out.
Other ideas?
Dry solder joint? Soldering requires clean surfaces and rosin flux and correct temperature.
Your project board is already wired in a manner you've not taked account of? Hence time to go and measure it.
I have destroyed three project boards and resister sets.
How?
It is hard quite hard to destroy a resistor, and project boards can be re-soldered a few times before the pads come off.
Do you mean actually wasted and not destroyed?
What am I doing wrong
Until we know what you are actually doing we can't tell you what you are doing wrong.
I am trying to do a simple voltage divider project with an Arduino uno
What is the "output" of the voltage divider connected to? Is it connected exactly the same on the breadboard?
...For example, you can't "power" the Arduino (or anything else) through a voltage divider. Voltage dividers are only for low-current "signals". If you connect any kind of load, the resistance of the load changes the resistor ratio, lowering the voltage.
Well...I am making progress but one Arduino Uno is no longer responding.
I am working with a Wemos D1 Mini Pro until I can get another Arduino.
The project I am working on is a 12v battery monitor for a boat (and to monitor temperature / humidity).
I was not happy with the project board I was trying to layout so I started over this weekend. I measured the resisters for the voltage divider.
I have tried to post this reply a few times and the photos have not worked, so once this is up, I will reply with photos next.
The ground from Wemos is connected to one side of the smallest resister (and the ground from the 12v source connects here too)
The 12v + wire from the source connects to one side of the larger resister.
The two resisters are soldered together and a wire runs from their connection to the A0 pin on the Wemos Board.
The output from the code is returning voltages that vary from 11.8 - 12.4 volts while the input voltage source is showing 12.3 constant. ( I am using a 12v power supply for a CCTV camera is source).
The voltage divider is showing output that is ranging 628 to 662.
The Wemos is emailing every minute (or 5 minute) as I test.
How can I get this more consistent / reliable?
Thank you
Doesnt really help. Can you put a circuit diagram - even a hand-drawn one?
So I'm guessing there are some solder bridges between lands on the other side of the board. 
From what I can see on that photo the divider is 100k:47k ? Is this correct? That's higher than
the recommended 10k maximum for analog pin drive impedance, so a 100nF cap to ground on
A0 is wise to reduce noise pickup and crosstalk between ADC pins.
From the numbers you give I calculate a divide ratio of 2.9:1, which doesn't match the resistors.
(Assuming Vcc = 5V, 10 bit ADC)
12.3 V / 3.9 = 3.15V, 3.15/5.0 x 1024 = around 640
A 2.9:1 ratio implies about 140k : 47k, which is different from the picture.
Is Vcc not 5V?
If you can provide a schematic of your circuit that will really help.
[ Actually I just looked up the Wemos D1 - its 3.3V only board, so that 640 count indicates about 2.06V at A0... ]
You can't get to A0 of a Wemos D1 mini directly to add a capacitor,
because the Wemos has a 220k:100k voltage divider build-in.
Don't use a voltage divider with a Wemos, because of that divider.
Just connect a single 1Megohm resistor between +12volt and the analogue pin of the Wemos.
Don't expect too much of the A/D of an ESP8266.
Leo..
Ah, that would explain it. The choice of external voltage divider impedance will interact with the on-boad
divider and cause confusion (as witnessed in this thread).
Adding a 1.2M external series resistor will give a full-scale range of 15.2V or so.