Struggling with power requirements for project

Hi there, I hope all here are doing well.

This is my first post on this forum so if I'm making any mistakes or missing any usual forum etiquette please let me know.

So my project is relatively simple, I am controlling 2 UVC light LED strips with an Arduino Nano, two HC-SR04 ultrasonic sensors and a dual channel relay switch. The entire circuit is powered using a 6.4V battery supply with high capacity batteries (3200mAh). The way the circuit should work is that the sensors act as a motion detector, and if a person or any presence is detected by either sensor, the LED strips need to be turned off. The LED strips are designed in such a way that they are powered by a mini usb input but the circuit of the strip is naturally open and the two open points need to be closed for the LED's to turn on, hence the relay switch. The relay is connected to be normally open for both strips and closes when any of the sensors detects anything.

The problem that I'm having is that there doesn't seem to be enough power supplied to the circuit to power everything. When the LED strips are on (circuit shorted or closed) the sensors are not able to detect anything and the relay switch doesnt flip (I've also noticed the on LED of the arduino nano is dimmer as well as the LED's on the switch), however, when the LED strip circuits are open, the sensors and relay switch work just fine. I've also tested the circuit using a multimeter and found that the voltage supplied to the Arduino when the LED strips are on is only 2.5V, while it is about 4.7V when the LED strips are not powered and the sensors work with the relay.

So I think the obvious conclusion here is that the LED strips are drawing too much power when they are turned on. The problem is I don't know where to go from here, if the issue is related to current or voltage, if I need to use a more powerful battery or if my circuit is just poorly built. If anyone has any recommendations it would be greatly appreciated. The attached image shows my circuit (rough, not exact). Thank you to anyone who took the time to read through all this.

I don't like a "help me plz" when I have to hunt down the pin assignments myself. So I didn't bother. They're unreadable in that fuzzy Fritzing.

But, if you are feeding 6.4V into the 5V pin of the Arduino, you are exceeding the maximum allowed voltage of 6.0V. If it's the VIN pin, 6.4V is barely enough, or not enough especially as the battery gets low.

The HC-SR05's are 5V devices too. So yes, you have some power problems. Also imagine how the battery voltage might sag if one or both relays are on at the same time.

If you have power for the strips, why are you running the system on batteries anyway?

You say the strips are powered from a USB, but you also say "I think the obvious conclusion here is that the LED strips are drawing too much power when they are turned on"... well that makes no sense unless the USB supply is too weak. Then the obvious test is to connect them to a better supply!

Where is this USB supply in the diagram? I don't see it anywhere.

Hi aarg, sorry for the low quality circuit picture, I was just trying to give a general idea of what the circuit looks like, but the software I used to draw it is quite limited. The mini usb's are connected to the battery supply, along with the rest of the components so the LED strips are powered by the battery via a mini usb connection, they just don't turn on unless the two points that I mentioned are closed, which is where the relay comes in.

Thanks for the input, I don't have another battery with me at the moment to test with, and I'm very inexperienced when it comes to batteries in general so I'm just looking for a more experienced opinion that I can go with. I was thinking of looking at replacing the battery with a 12V pack, do you think it would be sufficient?

Let's not be connecting 12V right now. I'd like you to comment on the incorrect power supply voltage problems I mentioned, while I make a coffee... :slight_smile: You are aware, I hope, that electronic devices always have some specified input power voltage value or range? Beyond which they will fail, or blow up?

Also, you don't need software to make a diagram. Just pencil and paper. You can upload it by taking a photo.

What's the current rating (amps or milliamps) for the LED strips? It may be listed as mA per foot or mA per LED.

Note that the mAH rating for the battery is an energy storage rating which indicates how long the batter will last, not the maximum mA it can put-out.

Sweet, thanks so much for taking the time to help. I'm not just going to replace the 6V with a 12V, I'm assuming I would need a voltage regulator or at least a buck converter to step the voltage down. I'm very much a noob when it comes to electronics so I'm not sure if I'm overthinking this, but if I use a voltage regulator to step a 12V down to 5V would I not just run into the same issue as before if the problem is related to a lack of voltage? On the other hand if its because the current drawn by the LED strips is too high I'm not sure how to go about fixing it, if I need to redesign the whole circuit.

I think you're on the right track with the voltage converter. As long as your battery can supply more power. Power is voltage times current. With a power converter, a good idea, the battery voltage doesn't matter as much as the continuous power that it can produce - as long as it is sufficient to drive the converter properly.

Hi there Doug, the LED strips each have a current rating of 0.5A, and have a voltage requirement of 5V.

What baffles me is, why have you not tested it running power from a simple 5V source like a wall wart? Some of them produce 2.0A at 5V. Then at least you know you have something that will work with a power converter.

Thats a really great idea. I tested it with a usb supply to the arduino but I didnt realise the max amp output from a pc usb is only 0.5A. I will try it now with a wall wart. If I power the arduino with a 5V 2.0A wall wart and then power the rest of the circuit through the 5V pin from the arduino will it be able to supply the whole circuit? I know there are power limitations on the arduino pins, just not exactly sure what the limitations are.

No, not that way. The Arduino has a resettable fuse that limits the current to the 5V pin. Do it the other way around - feed 5V to the entire circuit, apply that 5V to the Arduino 5V pin, it can input as well as output supply current.

Good morning aarg, just wanted to update you and doug on my progress. So I tested my circuit with a wall wart and the circuit worked, the only problem is that I'm prototyping with a breadboard and the breadboard power adaptor I have seems to be limiting the current available to the whole circuit, so while the circuit works perfectly with one LED strip, the moment I add the second one the relay's power LED's start to dim and the LED's light up perfectly. So I think its current limitations that are hurting the circuit. I will be getting my hands on some protoboard today and some solder and will try powering the circuit with a bigger battery through a power converter. I will let you know if I make any significant progress. Thanks again.

Sounds bad. Most "breadboard power adaptors" suffer the same problems as "Vin" on the Arduino.

When we refer to a "wall wart", we mean a 5 V one with a USB connector. To connect it to a "breadboard power adaptor" you need a male-to-male USB cable to connect it to the USB socket on the adaptor. The "Barrel jack" is like that on the UNO/ Mega - quite useless. :crazy_face:

OOh, yeah, sorry I was not more specific. So now you are going to have to be very careful about the battery power converter that you use. Your step down converter should be able to supply several amperes. I don't know of any off hand, I don't have any applications for them myself.

Hi, @yodafromstartrek
Welcome to the forum.

At this stage can you please post a circuit diagram.
Not a Fritzy image.
A hand drawn circuit, with components and pins labelled and power supply included.

That way we will all be on the same page with your progress so far.

Thanks.. Tom... :smiley: :+1: :coffee: :australia: