In order to overcome doubts in using AA batteries with Otto and understanding the reasons of why some Otto Builders have difficulties with them. Let’s have a look at the the various ways to power our Otto robots, to provide some useful advice:
When you want to use an Otto in stand-alone mode, the first problem to face is the one of how to power it, once it is disconnected from the computer’s USB port. Unfortunately, a faulty knowledge of the theme of powering sometimes leads people to make unforgivable mistakes, since the first result is often that of seeing the robot board go up in smoke and almost always irremediably, since from that moment it will not work any more.
In the premise it is good to point out that this article will deal with the ways to power the "Otto board" which is a combination of a compatible Arduino Nano board operating at 5V with the I/O shield although this could be applicable for the UNO boards in similar way.
THE INPUTS FOR POWERING
Everything we will describe in this post can be applied to all the kind of sources power supplies and batteries. We point out the need to pay maximum attention to the polarities: it is very important to connect properly the positive (red cable) and the negative (black cable) poles to the Otto board, otherwise there is the risk to see nothing work or even to make irreparable damages. In fact, while in some cases there are some intrinsic protections on the board, in other cases the polarity inversion might cause immediate damages!
Otto board has 4 possible powering inputs:
by using these 4 inputs (red arrows) we can have at least 8 different ways to power your Otto robot.
1. USB port from a computer
5V have to reach this socket (different voltages are not allowed, absolutely!), coming from a computer’s USB port, this is usually the case. There is a current limitation of 250mA or 500mA, meaning that robots like humanoid when have all 6 servos working at same time can experience some resets, depending on the USB port of the said computer, but generally is the safest, easy and simple way to power your Otto, program and test your new codes and creations very fast.
Powering by computer USB Port.
2. USB port from a power supply
If on the other hand you are using an external power supply that is provided with a USB port (in general, they are small size power supplies, suitable to power devices that are provided with a USB cable) the maximum output current (regardless of the one guaranteed by the same power supply, that in general is a maximum of 1A or 2A). So this option will give you the best performance for all Otto robots no matter how many servos uses, but some are limited to 500mA by the PTC self-resettable protection fuse.
Powering by power supply with USB Port.
3. USB port from a power bank
This one is handy for experimenting with small loads, requiring the same 5V, since it enables the dual function of powering and programming the board; the power limit imposed by the PTC fuse is 500 mA, and actually, these components tolerate up to almost twice the value before a protective intervention, but it is better to consider the nominal value; the polarity on the USB socket is a standard one and thus does not cause problems:
Powering by power bank with USB Port.
4. "Japan Jack" socket from a power supply
An external source must be connected to this socket, with the positive pole going to the central part of the jack, and the value must be ranging between 6V and 20V, even though the range recommended by the manufacturer is 7/12V, thus it is not advisable to use voltages that are lower than 7V or greater than 1V, if not in the case of a real need; 6V may not guarantee a proper stabilization on the part of the regulator, it is in fact needed to consider the voltage fall of the protection diode, placed in series at the regulator’s input (whose purpose is to preserve the board from destruction in the case of polarity inversion on the jack); while values above 12V would create an excessively high drop-out (an electric potential difference between the regulator’s input and output) that would cause a pointless overheating of the regulator, even with low levels of current draw.
The positive pole must be applied to the JACK’s central pin, the negative pole to the external one;
Powering by means of a JAPAN JACK socket.
Everyone at the end want Otto to be independent of a cable or plug, of course, it seems obvious, is a robot after all, but that comes with challenges, Before revealing the other ways, it is important to deal briefly with the problems connected with battery powering, since we need a robot independent from the home electric network. When deciding to resort to battery powering, the ratios between their capacity (usually expressed in mAh) and the power required by the Arduino board and the peripheral circuitry connected to it are often neglected, thus leading to results that are often disappointing (autonomy is very low, resets or the system does not turn on at all). In this figure we represented an overview of the most commonly used battery types:
We will focus on the ones in the left, AA alkaline batteries they must strictly be new, in the case of AA rechargeable batteries all of them must be fully charged. Lithium batteries could be the most efficient way to power your robot but they require special care.
5. Vin from 4AA alkaline batteries
Vin pin can be useful as input if an external voltage is needed and you only have 6V available, in fact the Vin socket bypasses the protection diode and the regulator may operate properly. considering the fact that the Vin socket is unprotected, so make sure the battries are good quality. The positive pole must be connected to the Vin socket, the negative one to the GND. In figure you can see Arduino powered via 4AA alkaline batteries to the Vin socket, nevertheless when many servos are used or the batteries are slightly used you can connect them to any 5V pin in the shield like in the next way to power your robot.
The Vin socket used as input or as output.
6. 5V from 4AA Ni-Mh/Ni-Cad rechargeable batteries
5V socket it is directly connected to the regulator’s output, thus the 5V to power external loads to Arduino can be drawn from it, the 5V socket can be even used to power Arduino directly, if having an external stabilized 5V source. AA rechargeable batteries come with lower voltage than alkaline only 1.2V connected in series they give us a total of 4.8V just enough to power our robot, it is important to use the high capacity and good quality ones.
The 5V socket used as input or as output, you can virtually connect to actually any 5V pin on the board.
Nominal voltage is 4 x 1.2V = 4.8V Fully charged they are 4 x 1.25V = 5V
True lowest voltage 4.5V will work but VCC will be 4.5V outputs so if source lower than 4.5V you will experience resets.
7. Vin from a LiPo 7.4V battery
These are also called as Lithium Ion polymer rechargeable batteries because it uses high conductivity polymer gel/polymers electrolyte instead of liquid electrolyte. These come under the Li-ion technology. These are a bit costly. But the battery is very highly protected when compared to the Li-ion batteries. It has Power density of 185 Wh/Kg. Very light in weight, but expensive. Might explode if wrongly connected. Should not be bent or exposed to high temperature which may cause to explosion. So this ones should be handled with care! This works similar with Lithium ion cells connected in series.
8. 5V from a LiPo 3.7V battery + DC booster
Lithium Ion Polymer rechargeable, similar to previous way, this ones uses a lower voltage LiPo battery of 3.7V but then we need to increase that to 5V, so for that we use a "booster" or step up, which will require some soldering involved. This works similar with Lithium ion cells.
NOTE: regardless of the input used, Arduino has a 3.3 V output socket to power loads operating at this voltage; in fact a second regulator, right for the purpose of generating 3.3 V, is directly connected to the 5 V. This socket cannot be used as input.
a small boost converter is required to reach 5V.
What if i connect 2 inputs at the same time?
Arduino is provided with a comparison circuit that controls a type P MOSFET; if a tension is found on Vin (powering from the JACK or from the Vin socket), the MOSFET is interdicted and the possible presence of voltage coming from the USB port is ignored; in the opposite case, the MOSFET will connect the USB port’s 5 V to the 5 V socket, hence below the regulator, thus powering Arduino.
Management circuit of the power conflicts
Therefore it is clear that if you apply the voltage to the USB port and an external source to the JACK socket at the same time, it will be this last one to power the circuit, while the USB connection will keep working for the data exchange with the computer and no longer as a power source. We remind that in both cases the 5V socket cannot be used as input, but only as output.
Which one should i use?
Having now a clearer picture on the subject of the power sources and the various inputs offered by Arduino, it is necessary to decide which of the latter should be used for each specific robot. The choice must obviously be made on the basis of the power source available, but also on number and type of servos to be powered.
Vin drop out voltage is 1.1V then need at least 6.1V (like new alkaline AA batteries) if a power source is higher than 6V but less than 10V you should connect to Vin
9. 5V from a LiPo 3.7V battery + DC booster + Charger
This is actually the "Ideal" setup if you are gonna use Otto constantly, you will be able to recharge (with an additional USB port) and have the most optimum power supply for your robot, LiPo batteries have an additional cost but for the long term is the best solution we have find so far. Although soldering is required here too. This works similar with Lithium ion cells.
notice the small blue chip on the left. that is the charger, comes with USB port to recharge the LiPo battery.
10. Power with the charger booster
Fortunately we have created a component that does all of this in one small package and affordable price, this battery charger and booster is very handy for powering Otto's since it comes with all you need to make you Otto easier to recharge and power you just need one small one 16340 Lithium Battery. It can be connected to any 5V port from the shield.
What are you using to power your Otto?
Do you know more ways?