I'm connecting the 5V pin of my arduino to the coils of the relay because my relay requires a minimum pick-up voltage of 3.75 as the Nano 33 Iot only has an I/O of 3.3V. The pick up current needed for the relay is 0.071A.
With that, if i were to use a bjt as a switch because i would like to control the relay with a digital output pin,
a) What would my collector current (Ic) be as it flows out from the 5V pin and through the coils and,
b) Would I still need a base resistor (Rb) if my DC current per I/O pin is 7mA from the Nano 33 Iot?
Hard to say exactly as you have no component values nor transistor type number.
But if the relay takes 71mA at 5V then by ohms law you have a 70.42Ω coil. You will get a 0.7V drop between emitter and collector by ohms law you would have a current of (5V - 0.75)/ 70.42 = 60.35mA.
[quote="Grumpy_Mike, post:2, topic:1153430, full:true"]
[quote="ntu-spgroup_fyp, post:1, topic:1153430"]
What would my collector current (Ic) be as it flows out from the 5V pin and through the coils
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Hard to say exactly as you have no component values nor transistor type number.
But if the relay takes 71mA at 5V then by ohms law you have a 70.42Ω coil. You will get a 0.7V drop between emitter and collector by ohms law you would have a current of (5V - 0.75)/ 70.42 = 60.35mA.
Thank you for the detailed calculations! Sorry, I was considering between the BC547 NPN or BC337 NPN.
So i wasn't sure how much output current the 5V pin from the arduino will supply as I couldn't find the value from the datasheet so I wasn't sure how the 5V can turn on my relay.
[quote="ntu-spgroup_fyp, post:1, topic:1153430"]
b) Would I still need a base resistor (Rb) if my DC current per I/O pin is 7mA from the Nano 33 Iot?
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Yes.
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The simple test is to connect the relay to the 5V power supply and see if it pulls in. Then you could measure the current with your DVM (Digital Volt Meter). Do you know how to measure current? It is different to measuring voltage.
How are you powering the Nano 33 IOT? Have you checked to see if you are getting 5 volts from the 5V pin?
Note the following from the description of the Nano 33 IOT:
Ah I'll probably do that once I have gotten the required items! Measuring of current will just require me to connect the meter between the relay ends and collector pin right?
Actually I have not connect my Nano 33 IoT yet as I'm still in the researching and designing phase of my project, as there is a budget I wanted to be conclusive in my calculations. But I'm about to get the required items so I will test it out once I get it!
Wouldn't it be better to directly connect both devices to a 5V battery or more?
I connect the Nano 33BLE to 18 volt battery to drive 2 DC motors.
I don't think it's good to get 5 volts out of the Arduino constantly. (Using 5V pin limit).
Unless the Pin VIN can work better maximun 21v.
I have tried moving some servo with the Atmega328 with 5V pin and they have burned my servos out over time, receiving power is easy, but delivering power is quite complicated.
And if you will charge the Arduino by USB normaly you can get more than 4V using the VIN pin, I am cheking with my Macbook USB and I am geting 4.72v at pin VIN of Arduino Nano 33 BLE.
I belive that you can use an old 5V mobile charger maximum 5V.
But take care, not use new chargers (like fast charge Samsung from S5,S6...and so long because they work with 9V some new can charge ultil 65w...and can burn your Arduino USB conection. You need a very old mobile charge like iPhone 2G until iPhone 5...or one that say 5V.... But take care, if you use more than 5V with USB port probably will burn your USB. Basic you will put 5V at USB port and get almost 5V with Pin VIN..... Or you can use a battery maximum 21v, but 21v it's not recommended also for a long period of time.
***** The above is just an idea.
Please consult with other users, I will tell you the idea that occurs to me, I am new and I can be very wrong
Look
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Powering from the 5V pin and USB at the same time should be avoided. This is because the circuit that controls the power from the USB is triggered from the VIN / barrel jack and needs to be above about 6.5V to cause the USB power to be isolated.
It won't damage your Arduino, but there is a chance that your computer may be unhappy and shut the USB port down. 5V shouldn't cause any damage though, but it may detect that something isn't quite as it should be and take steps to protect itself
Hello! Sorry for the late reply, just managed to see this.
You make a good point! Because I'm still at my designing phase, I would be connecting my arduino to my computer via USB because I need to upload codes as well.
But moving forward with the project, I'll also consider how to power my board without the USB anymore and perhaps some form of battery.
Currently I'm at my development phase so I'm still trying to understand the board processes and the power output to individual components.
Thank you for the insight! I'll be sure to check in again with any issues!
