Hello!
I am new to PCB Designing and I am using KiCAD for the first time. This is my first project as I am trying to design a prototyping board for an AVR ATMEGA32A. I want add both USB-B and USB Micro-B ports on my board for ease. I am using FT232RL as a USB to UART converter.
Currently I am using a two way switch in order to differentiate between the ports.
Can someone please tell me how am I suppose to add both of these ports without any errors. Any improvement and feedback will be appreciated.
He wants the user simply to pick the type B or micro B connector. A hub wouldn’t make sense as there are two host ports effectively… and only the single ftdi chip as downstream.
I just went through the USB2422 and USB3740B datasheets.
USB2422 wouldn’t suffice since I don’t need master and downstream ports. It was wrong of me to use the RPi as an example. I understood your context.
USB3740B will be sufficient since I can connect two ports on one side and send their output to a MCU.
P.S If possible, can you recommend a low cost alternative to USB3740B.
The Raspberry Pi does not offer dual connectors for a single USB port. The micro-B connector is used solely for powering the board (no data), and the four A connectors are host-mode data and power ports.
If you want the user to be able to use either a B or micro-B connector for the same USB port, that will require extra hardware or an adapter as noted in other replies.
USB requires controlled impedance data tracks (at least for the higher baud rates), but if you keep the wires short you can PROBABLY get away with simply putting the 2 connectors parralell to each other.
The shortest wire stubs will be if you put the connectors on top of each other, one on the top of the PCB and the other on the bottom. This will also prevent users from trying to plug in 2 connectors at the same time because the overmoulding is to thick and it won’t physically fit. You can also get away with using a single fuse (and capacitors) for both USB connectors.
Do note that your schematic is not complete. USB needs (pull-down) resistors for device detection.
For your basic 2.0 you can get away with alot as long as you keep them parallel. I’ve run adhoc traces over stupid distances out of need to be cheap (and usb just being a footnote in the product).
Do note that your schematic is not complete. USB needs (pull-down) resistors for device detection.
Only if you are designing with chips from last century. Most have it internal as part of state management and an external resistor will be a detriment to functionality in that case.
Also USB uses pull-ups for detection not downs.
The FT232RL does have the internal resistors and requires no extra components.
I have made changes to the existing schematic. As previously mentioned I want to use either a B or micro-B port to send data to the MCU. For switching purposes I have used USB-3740B.
In Arduino’s, the USB port supplies power while connected to a computer. I want to add that feature. Whatever port is being used to connect the board to a computer is also supplying power to the circuit. Please do let me know if I have implemented that correctly.
Feel free to make any other suggestions or improvements.
If you know users will only use one cable (which you could encourage by placing the connectors very close), then a simple direct connect should be ok.
If you want user option with ‘no unplug’, and a 5V charger power source, then a DPDT switch is a good idea - the cheaper TC7USB40FT mentioned above can be powered from the 3v3 of the FT232RL
… but if you want total freedom of power & signal sources, then you might want to also look at USB power switch devices. Those can protect from back-feed of the 5V power in the case you have two connected active 5V supplies.
