How to Make an OwlBot: the Bird Intimidator – Part 4: Upgrading the Power Supply

In this part of the project we’re going to be performing the fourth step of what will eventually be the OwlBot. The OwlBot will be a device that can be used as a bird intimidation tool to scare away pesky birds in the yard, around the house or barn, at restaurants, or in trees, bushes, and gardens. Hence, the phrase, “The Bird Intimidator”.

To learn why the OwlBot was created and what problem it was to solve, check out the story behind it all here.

The OwlBot (a.k.a. “The Bird Intimidator”) we’ll be making will be done in several parts. The OwlBot is an ambitious project. When complete, the OwlBot will sense motion. When motion is detected, the OwlBot should make owl sounds, perform varying movements, and flash its red eyes to intimidate and scare away pests. To put together all these tasks in one page would be too long and cumbersome, so we’ve decided to split each process we want the OwlBot to do into easy to accomplish chunks or parts as we continue on our goal to complete the OwlBot.

Prototyping the Circuit

Up to this point of the project we’ve been adding some of the items and modules that make up the OwlBot’s functionality, such as its PIR sensor from Part 1, its MP3 player and speakers from Part 2, and it flashing red LEDs from Part 3. As we move forward in the OwlBot project, we’re going to be adding a few more items to our prototype circuit that are more power hungry than what we’ve added so far, so we need to start thinking about upgrading its power supply.

When we get to Part 5 of this OwlBot series, we’re going to be adding to our prototype circuit a couple of solenoids and a DC motor, each wanting higher voltages than the Arduino can supply them, and each drawing more current. So, what we’ll do in this part of the project is add another supply voltage to our circuit, as well as keep our original 9V battery source to power the Arduino.

As mentioned in the previous parts of this build, I have been using The Ultimate DIY 3220-Point Breadboard that was made from a separate project. I have been referring to The Ultimate DIY 3220-Point Breadboard as “TUDIY” throughout this project to save me from having to say it’s full name every time.

DON’T WORRY! Even though I’ll be discussing how to make connections on TUDIY throughout the following prototyping steps, I’ll provide images of how to hook up items on a generic breadboard, so you can still follow along!

In Part 1 of this OwlBot build series, we connected the 9V battery power supply to the main power rail on TUDIY, and then added a DC power jack to the power rail to be able to plug that supply into the Arduino’s DC barrel jack receiver. If you’re participating in this build series and are not using a TUDIY as your breadboard, then you connected a 9V battery directly to the Arduino’s DC power jack receiver using a 9V battery snap connector and screw terminal DC barrel jack adapter.

In the next part of the OwlBot prototype build (Part 5), we’re going to be adding two solenoids and a DC motor to our circuitry. This creates a larger load on the single 9V battery we’re using because, not only are we trying to use it to power on the Arduino, we’re also using the Arduino’s 5V pin on less power hungry devices — like the PIR sensor, MP3 player, and LEDs — which also comes from the 9V battery supply, stepped down by the Arduino’s onboard 5V voltage regulator.

If we are going to want our OwlBot to work properly — like we want it to — and efficiently, we need to go ahead and consider updating our power supply now, before we run into any issues later. Trust me, I got the entire prototype circuit to work for me when all set up on TUDIY, but I ended up receiving unwanted voltage readings in my circuit, and the solenoids and DC motor seemed weak when powered by the single 9V battery supply. That’s why I needed to look further into creating a better power source system, so you wouldn’t have to!

Let’s look at an example circuit next, so that we can get an idea of some issues that we could come across if we don’t upgrade our power supply of our prototype circuit.

Looking at the image above, we can see a breadboard setup that demonstrates an example of what we’re trying to do with the OwlBot prototype circuit and its power supply.

The breadboard is set up with a 9V battery’s snap connector tied to the screw terminals of a DC barrel jack adapter. Also tied to the screw terminals of the DC barrel jack adapter are a couple of jumper wires tied to the left-side + and – rail of the breadboard (bottom rail in image above). On that same left-side power rail (bottom rail), I have a couple jumper wires on the + and – rail going to a multimeter (meter1).

On the opposite side of the breadboard, where the right-side + and – power rail is (top rail in image above), I have a yellow jumper wire on the + rail going to the 5V pin of the Arduino Uno and a white jumper wire going from the – rail to the GND pin of the Arduino Uno. On this same right-side power rail (top rail), I have two other jumper wires going to a second multimeter (meter2).

When the DC barrel jack adapter from the 9V battery is not connected to the DC jack of the Arduino, meter1 reads 9.05V, and meter2 reads 0.00V, as shown in the image above.

When the DC barrel jack adapter is plugged into the Arduino Uno’s DC adapter, then meter1 reads 5.29V, and meter2 reads 3.50V, as shown in the image above.

Q.) Why is meter1 not reading 9.05V across the battery source and meter2 not reading 5V from the Arduino’s 5V pin source?

Explanation of the Issue:

The behavior observed with the voltage readings on the multimeters (meter1 and meter2) is likely due to voltage drops caused by the load on the 9V battery, the 9V battery’s internal resistance, and the internal circuitry of the Arduino Uno.

1. Voltage Drop on Meter1 (9V Battery Source):When the 9V battery is connected to the Arduino Uno via the DC barrel jack, the Arduino’s onboard voltage regulator starts drawing current to power the board and any connected components. This load causes the voltage of the 9V battery to drop significantly.
2. 9V batteries are not designed to supply high currents for extended periods. As the current draw increases, the internal resistance of the battery causes a voltage drop, which is why meter1 reads only 5.29V instead of 9.05V when the Arduino is connected.
3. Voltage Drop on Meter2 (Arduino’s 5V Pin):The Arduino Uno has an onboard voltage regulator that steps down the input voltage (from the DC barrel jack) to 5V for the board’s logic and peripherals. However, if the input voltage from the 9V battery drops too low (e.g., 5.29V, as seen on meter1), the regulator cannot maintain a stable 5V output. The Arduino Uno’s onboard voltage regulator requires a minimum input voltage (typically around 7V) to produce a stable 5V output.
4. This results in a lower voltage on the 5V pin, which is why meter2 reads 3.50V instead of the expected 5V.

Why This Happens:

1. Battery Limitations: 9V batteries have a relatively high internal resistance and are not ideal for powering devices like the Arduino Uno that require a steady current. As the battery discharges or is subjected to a high load, its voltage drops.
2. Voltage Regulator Limitations: The Arduino Uno’s onboard voltage regulator requires a minimum input voltage (typically around 7V) to produce a stable 5V output. If the input voltage drops below this threshold, the regulator cannot function correctly, leading to a lower output voltage.

The reason why this may be an issue is that having one 9V battery just isn’t enough to power the Arduino, the 5V components in the circuit, and the higher power components in the circuit, altogether. When using a single 9V battery to power everything we need in the circuit, the circuit just doesn’t give the proper supply voltage each component needs in the entire circuit.

How to Fix This:

1. Use a More Suitable Power Source:Replace the 9V battery with a more robust power source, such as a USB power bank, a 5V regulated power supply, or a pack of AA batteries (e.g., 6x 1.5V AA batteries for 9V total).
2. Alternatively, use a DC adapter that provides a stable 9V or 12V output.
3. Bypass the Voltage Regulator:If you want to use the 9V battery, connect it directly to the Arduino’s “Vin” pin instead of the DC barrel jack. However, this won’t solve the issue of the battery’s voltage dropping under load.
4. Add a Capacitor:Adding a large capacitor (e.g., 1000µF) across the power rails of the breadboard can help smooth out voltage fluctuations caused by the load. However, this is only a temporary solution and won’t fix the underlying issue of the battery’s limitations.
5. Monitor Battery Health:Ensure the 9V battery is fresh and fully charged. Older or partially discharged batteries will exhibit more significant voltage drops under load. (This is part of my problem as well. The 9V battery in the image above read 9.05V, whereas a fresh, new battery should read higher than this, say around 9.4 – 9.6V)

How I plan to handle the power supply dilemma is by choosing the 6 AA battery holder as a secondary 9V power supply for the OwlBot’s prototype circuit. The reason that I’m using 6, 1.5V AA batteries is as follows:

1. Having battery packs makes the OwlBot more portable than having to plug in a wall wart DC adapter or USB supply. Although, these types of power supplies are preferable and provide a more stable voltage supply.
2. I need at least a 9V supply to power the solenoids and DC motor together off the same source. Having one 9V battery just isn’t enough to power the Arduino, the 5V components in the circuit, and the higher power components in the circuit.
3. I need the power supply to be somewhat small in form factor, to easily fit inside the owl figure being used for the OwlBot’s body.
4. Disposable batteries, for now, are easier to get the project going in the direction of getting the OwlBot complete.
5. AA batteries are generally more stable and more efficient than 9V batteries.

You can choose another option, if you like, but I’ll be choosing the simple solution of using a 6x 1.5V AA battery holder for now, with the possibility of upgrading later on down the road.

Q.) Are 6 AA batteries really more stable than one 9V battery?

Stability of 6 AA Batteries vs. 9V Battery:

6 AA batteries are generally more stable than a single 9V battery when it comes to powering devices that require a consistent voltage and current. The following explains why:

1. Lower Internal Resistance: The internal resistance of 6 AA batteries in series is typically lower than that of a 9V battery. For example, 6 AA batteries can have an internal resistance of around 0.9 ohms, while a 9V battery can have an internal resistance of about 1.5 ohms. This means that when a load is applied, the voltage drop across the battery terminals will be less significant with the AA batteries, resulting in a more stable output voltage.
2. High Current Capacity: AA batteries can supply higher currents without significant voltage drops. For instance, 6 AA batteries can supply around 3.3A with only a 3V drop, while a 9V battery may struggle to maintain its voltage under similar loads. This makes 6 AA batteries a better choice for devices that draw more current.
3. Capacity Considerations: In terms of capacity, 6 AA batteries (especially if using alkaline or rechargeable NiMH batteries) generally have a higher total capacity compared to a standard 9V battery. This means they can provide power for a longer duration before needing replacement or recharging.
4. Voltage Regulation: When using 6 AA batteries, you can achieve a stable 9V output (1.5V x 6) without the complications of a voltage regulator, which can introduce inefficiencies and potential instability if the input voltage drops too low.

6 AA batteries are typically more stable and reliable than a single 9V battery, especially for applications that require consistent power delivery. Before we get into how we are going to connect our new, secondary 9V power supply, let’s first get something out of the way that you should do for any project you create, and that’s creating the common ground of the circuit.

At this point of the OwlBot build series, we need to form a common ground for everything being added to our prototype circuit. Even though we are going use two different external power supplies, and one regulated voltage from the Arduino board itself — one directly from the 9V battery power supply, one from the six 1.5V AA battery pack (also 9V), and the regulated 5V provided from the Arduino board when it’s powered by the 9V battery supply via the barrel jack — we still need to form a common grounding path for each and for all components in the prototype circuit.

A common ground is just a path for all negative supplies in a circuit to connect to or to “ground” to. It is the reference point for voltage in the circuit and ensures that everything in our circuit has a complete and common path for current to flow to. Having a common ground in our circuit will ensure proper functionality of the circuit.

To form a common ground for our prototype circuit, we need to do the following:

1. If Using TUDIY: For the TUDIY breadboard that I’ve been using throughout the prototyping process of this OwlBot series, I took a white jumper wire to make a bridge connection between the negative supply rail of the onboard 9V battery power source of TUDIY and the breadboard section we used for the negative supply rail for the regulated 5V from the Arduino board we connected in Part 2 of the OwlBot series, as shown in the image above.
2. Next, I took another white jumper wire and bridged a connection between the negative supply rail of the onboard 9V battery power source of TUDIY and to the negative power rail of the same breadboard section we’ve been using on TUDIY for our prototyping, but to the side opposite the negative power rail we just bridged a connection to in the previous step above. Later we will connect the 9V supply from the 6x 1.5V AA battery pack and its negative supply to this same negative supply rail.
3. After making these connections, we can see that all negative supplies are connected to each other to form a common ground:
4. the bridged connection between the negative supply of the onboard 9V battery of TUDIY, and the negative supply rail for the regulated 5V from the Arduino board.
5. the bridged connection between the negative supply of the onboard 9V battery of TUDIY, and the side opposite the negative power rail of the regulated 5V from the Arduino board. This is where the negative supply of the AA battery pack will connect to.

1. If Using a Generic Breadboard: If you’re using a generic breadboard to prototype your circuit, then all you need to do is bridge both negative supply rails of the breadboard with a jumper wire, as seen in the image above.

Now that we have a common ground set up for our circuit, we can move on to connecting the battery pack of our new 9V power supply made up of six, 1.5 volt AA batteries.

As stated earlier, I’ll be using a battery pack that holds 6 AA batteries. The kind of battery pack that I’m using has 9V battery snap connector posts on it to be able to use a battery snap connector instead of wires, which makes it nice and easy to remove from the circuit later when needing to change batteries.

The only thing we need to do to be able to add the secondary power supply to the prototype circuit is to:

1. add the 6 AA batteries to the holder,
2. take a 9V battery snap connector and connect it to the pack,
3. place the black wire of the connector to the negative (-) power rail of the breadboard that we made a common ground on to the onboard 9V power supply of TUDIY earlier under Forming a Common Ground. This is the power rail on the side opposite the negative power rail we bridged a connection to for the negative supply rail for the regulated 5V from the Arduino board we connected in Part 2 of the OwlBot series.
4. Lastly, connect the red wire of the snap connector to the positive (+) power rail next to the negative rail we just connected to.

Our connections are complete and we now have two power supplies to power the solenoids and DC motor we’ll add to the OwlBot prototype circuit in Part 5 of the OwlBot project series. It’s not perfect, but it should work better than having one 9V power supply for everything in the circuit later.

Now that we’ve upgraded the power supply for the OwlBot prototype circuit, the next step in prototyping the OwlBot will be to prototype the OwlBot’s varying forms of movement. We’ll do this using a pair of solenoids and a DC motor. We’ll add the solenoids and DC motor to our prototype circuit, and then add to our code for the Arduino to be able to control the solenoids and motor to be activated while the MP3 player plays owl sounds and the LEDs flash when motion is detected by the PIR sensor. All this will be in Part 5 of the OwlBot project.

Thanks for trying out this neat project. Hope you had fun! If you're ready, go to Part 5 for the OwlBot project, where we'll add a couple of solenoids and a DC motor to our OwlBot. Remember to keep at it and stay motivated!