Hello,
I would like to use a USB keyboard with my 5v Mega 2560 PRO Mini but it seems that all the USB Host Shield Mini's require a 3.3v Mega board.
Are there any 5v mini USB Host Shields available?
I have seen a few posts regarding level shifting chips but not in enough detail for me to understand how I would hook it up.
Any pointers would be appreciated.
You may find the following useful, with respect to level shifting:
https://learn.sparkfun.com/tutorials/bi-directional-logic-level-converter-hookup-guide/all
I am not familiar with the Mega 2560 PRO Mini, but the USB standard does specify +5VDC for powering the connected device, and a keyboard is more than likely going to be designed for that.
For the 3.3VDC mini USB host shields, you should be able to use a 3.3V LDO regulator to supply the required voltage to the host shield, and level-shift the pins that communicate with the Mega 2560 PRO Mini, but I would keep those to an absolute minimum.
Still, you would have the problem of supplying sufficient power to the keyboard, through the USB interface, for proper operation.
Thanks for the quick response and links. I think I can provide +5v to the host shield VBUS line to provide power to USB device.
Level converter looks pretty simple, but I think I have 6 lines to convert (SPI, INT, Reset) so I guess I would need two of them (or perhaps a level shifting chip that has 6+ lines).
Maybe something like: CD4504B (ACTIVE) CMOS Hex Voltage-Level Shifter for TTL-to-CMOS or CMOS-to-CMOS Operation would be appropriate.
I just looked in my stock of goodies, because I seemed to recall that I had bought a USB keyboard host board board for a project that I did a few years ago....and the spare board (I never buy just one of anything) was in the top drawer....I tracked down the supplier, and you may want to look at their product listing page to see if this will work for you:
http://www.hobbytronics.co.uk/usb-host-board-v2?language=en&keyword=usb%20host
You can order it with firmware specific to the following use cases:
Flash Memory Stick
USB Keyboard
USB Joystick
CDC Communications Class
USB Mouse
PS3 Dual Shock Controller
PS3 and PS4 Dual Shock Controller
Serial Driver for FTDI, CP210X, PL2303, CH340/1 and CDC
MIDI Device
USB Modem
Hopefully this is appropriate for your needs.
[EDIT]
The board is selectable for 3.3V or 5V use, by the way.
I actually saw those, but I don't think it is exactly what I need. I really need the raw keyboard codes (with alt/ctl/shift modifiers) and it looks like that adapter is a little simpler sending just key values serially.
I am seeing this page that seems to be just what I am trying to do. I think I'll try a level-shifting chip and try to leave the MISO line as a direct connection (3.3v level) back to the Mega.
Or maybe one of these would work: 74LVC245 - Breadboard Friendly 8-bit Logic Level Shifter