How to power a small wifi module connected to Teensy 4.1?

J

Jeremy Smith

Member
I have a project that is running perfect in terms of code and serial communication. I have a keyboard that is connected to the teensy 4.1 via its usb host pins, and the teensy then connects to the PC via its built-in micro-USB connector. I can type on the keyboard and the teensy receives the data, modifies it, and sends the modified data as keystrokes to the PC. The teensy receives data from this wifi module: bw-16 rtl8720dn breakout board which is connected to the teensy 4.1 via UART connection. Both the wifi breakout board and the teensy 4.1 are connected to the PC via usb cables.

Now that everything is working, the last part of the project is to replace the RTL8720DN breakout board with the smaller module version: RTL8720DN module and eliminate the second usb cord that was running from the breakout board to the PC.

Here is an image to visualize desired setup:

project description.png

How will this module receive power? Can the teensy 4.1 draw power from its usb cord to deliver enough power to itself and the wifi module? If so, how do I connect?



Thanks,
Jeremy
 
Jeremy Smith said:
Can the teensy 4.1 draw power from its usb cord to deliver enough power to itself and the wifi module?
Click to expand...
Maybe. You might need an external power supply for all of this.
It's hard to say because the specs for the wifi board say it may require up to 450ma @ 3.3V. So you can't just connect it to one of the Teensy's 3.3V pins without risking overloading the Teensy's 3.3V regulator. You could use a separate 3.3V regulator connected to the Teensy's VIN pin (which is directly connected to 5V on the USB port), but when you add up all the current required for the Teensy, the USB keyboard and the wifi board it might exceed 500ma, which is the maximum current a regular USB port will supply.
 
What about using a usb cable splitter such as this? I am surprised that a USB port has such a limited current supply since it is so common to see usb cable splitters that can be used to power multiple devices. I wonder if I used that micro-usb splitter and stripped one of the wires so that I could feed the 5V usb wire to a step-down converter and feed that into the rtl8720dn 3.3 vin?
 
The current limit is at the source. Your PC would hopefully shut down the port if the current exceeded 500mA
 
Thanks. Doesnt USB 3.0 support 900mA? And can anyone confirm whether my connection idea with the cable splitter would work?
 
You could use that cable splitter to power two devices (up to the current limit of whatever is providing power to the cable splitter), but the two devices would not be able to talk to each other thru this cable.

Mark J Culross
KD5RXT
 
That cable splitter seems the opposite of what is desired
[B]Power up to Two Micro USB Devices at Once from a Single Micro USB Port[/B]

Design seems to be one USB cable to power two devices, that is not like old external hard drives or CD drives where they plugged into two ports on the host to get double power with one data/power and the 2nd power only.
 
You must log in or register to reply here.
Back
Top