Connecting arduino nano to car battery while running

I'm still a total noob when it comes to electronics so please don't be too rough... :sweat_smile:

I read a few posts and basically understand that while a 12-14v battery would work with an arduino, the noise and voltage spikes caused by a car's charging & starting system are not favorable. The best way to resolve the issue is with a regulator, something to filter the noise, and protect against spikes. I am extremely incompetent when it comes to making my own circuit so I'd much rather find something that does everything I need already assembled.

I found this unit on ebay EBAY LINK and am hoping it will do pretty much everything I need. It uses a L7806/LM7806 (is LXXX & LMXXX the same?) regulator, some capacitors, and has multiple v-out pins if I need them. It's rated for 8-35V with an output of 6V & 1.2A. I would add a fuse in serial between the battery and this unit, and then wire the arduino to it.

So my questions are: 1. Is this unit sufficient to use in a car while starting and running. 2. Would a 2A fuse between the unit and the 12v be required/sufficient protection against surges?

Do you have any equipment for working with electronics?(soldering iron, multimeter)

This would be a good starter project, and you’d get something better suited to the job than the board you linked to (IE a big series inductor would be of use!).

The parts needed, you probably already have in broken electronics around the house, can make the inductor if you want to.

Yes I have a soldering iron, multimeter and plenty of wire. I regularly work/modify my car and do solder wires together when I have to but I definitely don't enjoy it. I just figure if there's a product that costs $3-4 that does the job, I'd rather use that than build my own.

hello :) do you know what you want to use in your project? like leds? LCD with backlight? to have an idea of the current consumption of your circuit :) because with linear regulator and over 50mA of current it will be hot with the little heatsink of the picture or use a little switching regulator. some parts exist with the same package as a standard 7805 TO220 casing :)

I have 2 projects in mind, and both would be ongoing.

The first would be on an old motorcycle and I want to monitor rpm using either a hall effect or IR sensor, temp at different locations, maybe an o2 sensor, and display the info on a backlit LED.

The second would be for a car and I’d monitor rpm, throttle, temps, fuel gage, and display on a backlit LED.

I've seen the LM2940CT-5 voltage regulator recommended for this purpose. It is apparently basically an automotive version of the LM7805 you linked to above. I have some on order for my motorcycle project.

So I found a circuit diagram. Can anyone tell me if this would be sufficient for in car use? It would not be near engine temp, and would be suspended using rubber dampers to limit vibration.

What’s the main difference between LM2940CT & LM7805/6 that would make it more suitable for in car use? Could I unsolder the 7805 and solder in the 2940 in it’s place?

This is a basic linear regulator circuit with a diode bridge in front. It will give you the voltage you require with the correct regulator chip.

As has been said before, if you are drawing more than minimal current at 12v input you will have a hot regulator.

At .5 amps and 14 volts with a 5 volt regulator, you are dropping 9 volts across the regulator.

As power = voltage x current, you have 4.5 watts dissipation. This will make the regulator very warm.

As has been advised, you will be much better off by using a switching regulator. There are many available from eBay and hobby stores.


Can anyone tell me if this would be sufficient for in car use?

No, it isn't. You need protection for voltage spikes upwards of 120V in front of the diodes/regulator section. Here are some ideas:

I've allready done a project like that (in 1999) for a scooter called "Twister" with speed, Km, clock, temp and even voice!, it was able to be stopped by remote control for scooter jacking with a great "welcome" message on the LCD xD

I was using an LM2940 and the power dissipation of the regulator required a little CPU fan over the large heatsink! so for your application it's best to use switching regulator. buy a cheap car lighter to USB adapter if you want. they are based on MC34063 chip in general but important note: add a rectifier bridge + cap before like you've said just above + 24V TVS diode. in a scooter or little bike if the battery is removed or died the voltage is more an AC voltage line than DC. and can go over 30V

picture of the beast ;) the power board the control board (talking together with I²C protocol)

vintage electronics now xD But I keep it in my office to remember my teenage projects period :D 1999...same period as when I won the French trophies robotics.....souvenirs...

Thanks all.. I'm learning a lot. I think it's a good idea that I DO make my own circuit for this to make sure all the bases are covered and to be more confident in my setup. I didn't really understand what Genesis meant in the earlier post regarding the switching regulator, but I do now. I'll definitely be using one in my circuit.

I'll draw up a schematic using all the suggestions mentioned here and share what I got.

Genesis, that's an awesome setup you got!! Might be vintage electronics to you, but to me this looks like the work of a technological genius!!! It will be some time before my bike will have a working setup, but I'll make sure to PM you a picture when it's done.

no problem I'm curious to know your system :) about the TVS (Transient Voltage Suppressor) or "transorb" "transil" diode it's a diode like a zener one but with a more vertical Ir(Vr) response for example a 5V TVS will draw current if the voltage is more than 6V most of the time the 5V electronic circuitry is not damaged because the Transorb diode is very fast.

But the diode position in the circuit is very important to be efficient! The diode must be installed near the power supply feed before the electronic components to protect.

I always put one for the 3.3v and 5V supplies of my electronic designs like SMLVT3V3 and SMBJ5.0 in SMD even if theyr are not always soldered on the PCB (in case of problem the PCB is ready to be equipped)

it protects the electronic in case of overvoltage (regulator failure, error etc....) Each arduino board should have one because it's cheap and it works very well

the 1N5908 is a good one in through hole mounting (you can see it on the last picture at the bottom right near the varta battery) For your application a SM15T18A could be a good choice to clamp voltage more than 18V at the regulator input (12v battery)

Wow.. most of what you wrote went way over my head... I'm going to try to get a better understanding, but I doubt any of it will sink in.

While I was researching switching regulators I came across a few product that may be able to do everything I need. Any comments?

  1. Would something like this simple dc-dc converter work for my application? It states that it has overload / over-current / over / low voltage protection, stable performance.

  2. An UBEC like this?

lxrubin: Yes I have a soldering iron, multimeter and plenty of wire. I regularly work/modify my car and do solder wires together when I have to but I definitely don't enjoy it. I just figure if there's a product that costs $3-4 that does the job, I'd rather use that than build my own.

What car and age is it? Many modern cars have another cigarette light outlet on the centre console, theses are called accessory sockets and are regulated and limited to 5Amp (on the cars that I saw of this nature).

Just a note, crimp to wires, especially in a car!

like explained above try to find a car lighter adapter to USB. it's a cost effective solution if you don't need more than 1A of current.

It would be going on a 2001 Golf TDI and a 1972 Honda CB350. The Golf has 1 plug up front and 1 near the hatch. I was under the impression that while a cigar-USB charger was adequate to charge a battery (like in a smartphone), it could be harmful to a microcontroller. If that's not the case then I will diffidently go that route instead. I could wire up a usb plug to the bike's + & - since it obviously doesn't have any factory cigar plugs.

no a car lighter adapter is simply a switching power supply like any other ;) if you want a more secure system you can choose a TI point of load like PTN78020W or traco power modules but it's not the same price ;)

I think I might have found a product that'll meet my needs. This is good because I'll be able to connect it to the bike easily and not have to use the cigar lighter outlet in the car, thus being able to hide it neatly. Also, I'll be able to use up my Amazon gift card :)

It's a buck converter with 3A max and simply has a 12v + & - wires and USB output. Could someone confirm that something like this would protect my arduino from voltage spikes and noise?

Amazon product page