how do i know what battery(how much ampere and voltage) my circuit needs to work perfectly?

i really love to make a lot of things but i always have this problem that i don't know how can i determine what battery(with how much voltage and amp)my circuit must have to work perfectly! please help me:( for example i have two circuits.circuit 1 includes:arduino uno ,2 servo motors and a DFplayer module and an led but i don't know is a 7.4 voltage Lipo battery with 1500mAh suitable for it or not??? and circuit 2 includes:arduino uno,L298 driver & 2 dc motors & 2 ultrasonics sensor but i don't know what battery does it need? i really love to learn it (determine the battery my self)

• You can guess/calculate/measure the current being used. With that you can calculate how long the project can run on the battery you want to use. You then have the choose if that's a reasonable runtime. Thought there are a lot of tricks to reduce the current being used. For example putting the Arduino in sleep mode. Using an Arduino Pro Mini instead of and UNO, so you don't have the USB chip using up power. etc. – Gerben Apr 5 '20 at 16:26
• thank youuu, but is there any faster and easier way?it's too time consuming:( – amir Apr 5 '20 at 16:35
• Even 7.4v looks okay for powering the Arduino, it is not a straight answer whether 1500mAh is enough, it also depends on how long you want the battery to last. – hcheung Apr 6 '20 at 12:07
• @amir this calculator might help. You don't have to be very precise. You just want to get a rough runtime calculation. Like, does is run for hours, days, or months. I often do the first rough extimate this in my head. Then I might do some measurements, or look at the current consumption specified in the datasheet of the different components. Shouldn't take too long. – Gerben Apr 6 '20 at 12:54
• @hcheung thank you – amir Apr 6 '20 at 15:54

TL;DR: You really need to know what components you have and you need to find datasheets. In the datasheet, you find what voltage the component requires.

Don't care too much about amperes in the beginning. If you get the voltage right, each component will just draw as much current as it needs.

An Arduino Uno operates from 7 to 12 Volts, so 7.4 V is ok.

"Servo motor" is simply not enough information. There are servo motors for 4.8 V, some for 6 V and others for 12 V. There are even AC servo motors for 240 V~.

DFPlayer is for 3.2 V to 5 V, so it shouldn't be powered directly off the 7.4 V battery. Maybe it can be powered from a 5 V pin of the Arduino. Since they power it from the 5 V pin, it seems to be possible.

Also "LED" is not a term that is good enough. Is it Infrared, Red, Yellow, Green, Violet, UV or white? Depending on the color, it needs something between 1.6 and 3.0 V. Therefore, you need a resistor. What's the use of the LED? Do you need to turn it on and off by Arduino, or can it just be always on from the Lipo battery?

The L298N has a supply voltage from 2.5 V to 46 V, so 7.4 V is fine.

Next, "DC motor" is not specific enough. I have seen 3 V, 5 V, 6 V, 12 V, 24 V.

Also, for ultrasonic, there are SR04 and SRF05. These two operate at 5 V. But if you have a different one, that may not be the case.

• it seems that you are a professional teacher and i think you can help me for this question too:i can't understand how much this lipo battery(7.4v) is charged.is there a way i can find out what percentage is charged?or can i make something for it with arduino or anything else that shows what percentage of the it's charge? – amir Apr 6 '20 at 11:20
• thank you so much sir for your help , my servo is MG995(4.8V-7.2V). my led is full color and i turn it on and off by arduino.im not sure but i think my dc motor's voltage is 3volt.my ultrasonics are srf 05.i wanna make a circuit that it works like this:when i turn on the switch servos and DFplayer(circuit1) start working but circuit 2 is off and when i turn the switch off, the circuit 1 will also turn off then dc motors,L298 and ultrasonics(circuit2) start working .is that possible mix two circuit with one arduino? do you think my lipo battry (7.4v)is enough for all of these? – amir Apr 8 '20 at 10:09