Use RP2040 wifi without computer

[Requiredusername]

I’m an engineering student working on a lab project, we assembled a robot that has to follow a course, attach to a trailer, then bring it back. the robot is controlled by an arduino and a shield

that came with the robot kit. The trailer hitch is plastic with a hole and sandwiched by washers so my team decided to use an electromagnet to attach the trailer and tow it. The robot can be remote controlled once it gets to the trailer by itself. We tried using unused pins on the shield to power and control the electromagnet but the pins don’t turn off when they’re supposed to so the magnet never turns off. We weren’t able to find the cause of problem so we decided to use a separate arduino and power source for the electromagnet, and I want to use my nano RP2040 because it can be remotely controlled. I’m thinking of using it to trigger the base pin on a mps2222a transistor.

I got this setup to test it out:

It works if it’s connected to a computer but not if it’s just connected to a power source, because the tutorial I used makes me open the serial monitor to create the access point. Since the computer can’t be plugged into the board when the robot is going through the coarse I need it to work without a computer.

My questions are:
1 can I use the Wi-Fi feature of the nano RP2040 without the serial monitor? If so is there a tutorial that can help?
2 is using the mps2222a transistor a good way to control power to the electromagnet as shown in the second picture?

Any help getting the RP3040 working independently would be appreciated. And any other suggestions or advice would be helpful because I don’t have much experience with this.

[PerryBebbington]

Hello @Requiredusername

Welcome and thank you for a well presented question.

With regards to your hand drawn schematic showing the drive to the electromagnet please read these tutorials before proceeding any further:

Common ground and why you need one

A common mistake for people new to electronics is to have 2 circuits fed from different power supplies with signals passing between the circuits, but with the grounds not connected. This leads to questions asking why the project doesn't work. You don't have to spend long reading the questions on this forum to see this is asked often. Here I attempt to explain the problem and why it matters to connect the grounds. Note that in all of the schematics that follow I have used a battery as a power sup…

Flyback diodes and why you need them

Any component that relies on an electromagnet or coil of wire for its operation will be inductive, that is the nature of coils of wire. Common examples are relays, solenoid and most types of motor. It is standard practice to put a 'flyback' diode across any inductive load in order to catch the back emf from the inductor when the current is interrupted. This requirement is usually taken at face value without being backed up by any kind of test results or evidence. This tutorial provides the evid…

You need to understand the principles of both. Also, as you are using a bipolar transistor please look up how to connect one for common emitter use. A MOSFET would be a better choice however. I note that you have not stated how much current your electromagnet takes, this is essential information before choosing a transistor to drive it. Please find out and tell us.

I have no advice to give for your other questions.

Good luck with your project.

[PaulRB]

To answer your questions:

1. Yes. Any tutorial you can find will/should work with or without serial monitor. The problem you have us more likely to be related to the power source(s) you are using. USB provides a well regulated 5V power source up to 0.5A current, which is enough to allow wi-fi to run correctly. When not connected to USB, how is your project powered? (I am worried that your answer will include a 9V battery!)
2. Maybe not, and certainly not as shown in your schematic. As @PerryBebbington says, you must have a flyback diode, or the transistor and maybe the Arduino will be damaged, and the transistor will not switch on without a common ground. Also you must have a current limiting resistor on the base of a BJT, otherwise the Arduino pin can be damaged. Depending on the current drawn by the electromagnet, you may need a higher power transistor, preferably a MOSFET such as IRL44Z or similar (one with a logic-level gate, suitable for a 3.3V logic input). If you don't know the current draw of your electromagnet, use a multimeter to measure it by connecting it directly to the battery, or measure the resistance of the electromagnet with the multimeter and calculate the current using Ohms law.

[studiogamma]

Is there a line like this in the code

If (!Serial) { }

This will hang up when not connected to the computer.

Post your code that would help