I'm looking for an IC that I can drop into an Arduino project to measure the voltage level of a battery. The battery voltage will often be higher than an Arduino or it's power regulator can handle, so I'm looking for an IC that is dedicated to this purpose.
You don't need an IC, you can use two resistors to make a potential divider.
Choose resistor values so that the voltage going to the Arduino analogue input is always less than 5V, and then multiply the voltage measured by a scaling factor for the resistor values chosen.
Just trying to get a simple voltage monitor set up for my volunteer ambulance service, so we can ensure that our EMT's never run to an ambulance with a dead battery.
Anyone have any advice here? I've been doing some reading that Zener diodes may be a good fit here? How would I configure the circuit? I think I need two resistors to step down the voltage and current to something the Arduino can handle, and then measure the voltage, and I need the Zener diode (along with another resistor) to send the voltage/current to ground when it goes past a certain point. Does that make sense?
Sorry, you're right. I read that, but I forgot to write back that I still had a question on that: is it possible to choose resistors capable of handling the voltage spikes, while at the same time still being able to provide me with the "true" voltage of the battery that I can read with the Arduino?
osmosis311:
Sorry, you're right. I read that, but I forgot to write back that I still had a question on that: is it possible to choose resistors capable of handling the voltage spikes, while at the same time still being able to provide me with the "true" voltage of the battery that I can read with the Arduino?
You can use quite high values of resistor for your voltage divider, say over 10kΩ. The resistors will easily withstand voltage spikes that may occur. The question is whether the input of your Arduino will withstand spikes above the Arduino's Vcc (including when its Vcc is zero) and spikes below ground. In another recent thread on this subject contributors claimed that the voltage divider will protect the Arduino and that is almost certainly true (if the resistor values are over say 10kΩ).
Why use an Arduino to measure car batery voltage (unless you want to use it for other tasks).
You can pick up a 2-wire LED voltage module from ebay for a few dollars.
Arduino can measure a car battery voltage with ~15-20mV resolution (steps) with two resistors.
If you choose the values correctly, you don't need zeners. Zeners leak and add non-linearity.
A 10k/22k voltage divider protects the arduino to 38volt (1mA input protection diode current).
Adding a 100n cap from input pin to ground eleminates spikes.
Another question was if the module from post #3 was able to measure a few hundred amps.
Sure. Try connecting the two current terminals across a piece of battery wire.
0.001ohm cable resistance can measure 320A. Use an oline wire resistance calculator.
Leo..
Wawa:
Arduino can measure a car battery voltage with ~15-20mV resolution (steps) with two resistors. If you choose the values correctly, you don't need zeners.
Exactly. And if all this is an exercise to determine if the battery is flat or not, we don't really care about resolution anyway. Given the dividers in Crossroad's example... well, if the zener does end up conducting, you'll find you have problems way bigger than a blown arduino. Besides, if this is an ambulance, isn't there some sort of isolation/protection/bus seperation built in already? I find it hard to believe that anyone would run equipment right off of 12V rail?
Thanks for all the guidance here guys, really appreciate it!
I'm using an Arduino for this project, connected to an Adafruit FONA (GSM board; eventually a Particle Electron), so that when the voltage gets "too low" it will automatically sent a text message alerting someone to come and start it / charge it up.
After watching several Youtube videos of people who have built automotive voltage sensors, I'm not convinced that these 200V spikes are something that I really need to worry about.