RPI Level Shifter Hat

An open source Raspberry Pi Hat for bidirectional 3V3 to 5V level shifting

This device is intended to allow communication between a Raspberry Pi and a 5V microcontroller such as an Arduino.

Example:

RASPBERRY Pi <==3V3 Signal==> RPI Level Shifter Hat <==5V Signal==> Arduino

Make sure to check the steps given under Usage & Setup

Features

compatible with Raspberry Pi 2/3/4 (rev_00 and rev_02)
compatible with Raspberry Pi Zero / Zero W (rev_02 only)
Bidirectional level shifting for all GPIOs
Enable level shifter with RPI Pin 37 (GPIO Pin 26)
Optional 5V power in / out
Optional Raspberry GPIO extension Header
TXB0108 TI level shifter ICs (Datasheet)
Enable indicator Led
Power indicator Led
Optional external enable (rev_02 only)

Get PCB kits here:

https://www.tindie.com/products/chris_wag/rpi-level-shifter-hat/

https://www.ebay.de/itm/254895227518

Mounting Hardware

1pcs 40 Pin Header Female (20x2 Pins)
1pcs 40 Pin Header Male (20x2 Pins) (optionally 0 or 2)
1pcs screw Terminal P= 5mm (optional)
4pcs M2.5 x 12mm Standoffs
4pcs M2.5 x 5mm Screws

Usage

Solder your Pin Headers as you need them. Make sure to mount the female header for the Raspberry on the 3V3 side on the bottom of the PCB. See the picture below. If you want to use 3V3 signals from the Raspberry directly also solder male headers to the footprint maked RPI GPIO Extension.
Optionally wire a 5V power supply in. This will be used to power both, the Raspberry Pi and the Levelshifter HAT. This should be done if you use lots of the 5V outputs with higher current draw
Configure your GPIOs as Input or Output as needed. See Examples for a python configuration sample.

Assemble as shown here: (Make sure to connect the Raspberry to the 3V3 side)

Setup

Enable after boot and set GPIO drive strength

Install wiringpi on the Raspberry in order to set GPIO drive strength.
```
sudo apt install wiringpi
```
This allows us to increase the standard drive strength of the GPIOs from 8mA per IO to 12mA, 14mA or 16mA. Higher drive strength can be required to trigger the direction detection circuit on the level shifter ICs for more demanding 5V circuits.
Auto configure GPIO drive strength automatically after boot up. Therefore we add the command "gpio drive 0 6" to the autostart sequence
```
sudo nano /etc/rc.local
```
[Optional] Add the following line before "exit 0":
```
gpio drive 0 6 &
```
The value 6 in the end sets the output drive strength from the default 8mA to 14mA. This should help to reach the 5V logic level for more demanding output configurations.
Enable RPI Level Shifter Hat automatically after boot. This is done by pulling GPIO 26 high. You can use Wiringpi or a python (see step 4) to do that.
```
sudo nano /etc/rc.local
```
Add the following line before "exit 0":
```
gpio -g mode 26 out &
gpio -g write 26 1 &
```
[Alternative to step 3] Copy the script "enable_rpi_logic_level_shifter.py" from the folder "Examples" to a local directory on your raspberry and add it to the autostart file as follows:
```
sudo nano /etc/rc.local
```
Add the following line before "exit 0":
```
python /[insert local path to the enable script]/enable_rpi_logic_level_shifter.py &
```

After this setup your rc.local file should look similar to this (Content depends on your version of Raspberry OS):

   #!/bin/sh -e
    #
    # rc.local
    #
    # This script is executed at the end of each multiuser runlevel.
    # Make sure that the script will "exit 0" on success or any other
    # value on error.
    #
    # In order to enable or disable this script just change the execution
    # bits.
    #
    # By default this script does nothing.

    # Print the IP address
    _IP=$(hostname -I) || true
    if [ "$_IP" ]; then
    printf "My IP address is %s\n" "$_IP"
    fi

    gpio drive 0 6 &
    gpio -g mode 26 out &
    gpio -g write 26 1 &
    #python /home/pi/gpio_test_OUTPUT_with_Enable.py

    exit 0

Versions

rev_00

initial release

rev_02

external enable pad added
RPI Zero screw holes added
correction & optimization of silk screen

Warning

This design is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY. Without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

License

License text: https://creativecommons.org/licenses/by-nc/3.0/

lausdahl/rpi_level_shifter_hat