Raspberry Pi Power Switch “PowerBlock”

The dimensions of the PowerBlock PCB are chosen such that it exactly matches the two mounting holes on the opposite of the USB sockets of the Raspberry Pi models A+ and B+. The PowerBlock PCB comes with the same round corners as the Raspberry itself and give it a neat look. Regarding the GPIO usage the PowerBlock is attached to the first 2×6 pins of the Raspberry Pi GPIO header.This addition makes it possible to not only mount the PowerBlock to the Raspberry Pi model A and B, but also to the Raspberry Pi Zero. Here are some exemplary images for the various models:

The PowerBlock PCB is attached to the Raspberry with a 2×6 pin female header. This header makes use of pins 1 to 12 of the J8 header. This header is used for connecting the voltage and ground pins as well as the status pins between the RPi and the PowerBlock. The PCB is kept as small as possible so that you can easily access all other pins that are not used by the PowerBlock.

The PowerBlock has the same USB Micro connector as the Raspberry Pi. That means you can simply use your existing USB Micro cable for powering the RPi.

To control the power state of the Raspberry Pi the PowerBlock provides an interface for attaching a toggle switch. The on-board microcontroller monitors the state of that switch as well as the one of the Raspberry.

The current power state of the Raspberry Pi can be indicated with a 5V status LED that can be attached to the two pins that are provided by the PowerBlock. A 220 Ohms resistor limits the current of the status LED. You will find a load variety of possible LEDs that fit these values. You can find one here.

These possible states can be “off”, “booting”, “on”, and “shutdown”. The different states are indicated with easy-to-distinguish static and pulsing patterns.

Side note: The maximum allowed output current of the status LED pin is 40 mA.

The PowerBlock can also be used without directly attaching it to the GPIO header of the RPi: There are individual pin outs for the 5V input voltage, the 5V output voltage, as well as for the control signals S1, and S2. This gives you a maximum of freedom for your project. The connection between these pin outs and the Raspberry Pi need to be as follows:

S1: pin 12
S2: pin 11
5V OUT +: pin 2 or pin 4
5V OUT -: pin 6 or pin 9


			

The Power Switch logic is implemented with the help of an Atmel ATtiny85 microcontroller. If you want to you have the possibility to access the microcontroller with the ISP header. In this way you could reprogram the microcontroller with whatever functionality you like.

The PowerBlock is also prepared for connecting a DC barrel jack adapter. The hole dimensions for the barrel jack adapter are chosen such that most of DC barrel jack adapters should fit. The exact footprint of looks like this:

One DC Barrel Jack that matches these dimensions can be found here.

If you want to provide a switched 5V voltage to another device, you can solder an optional USB A connector to the PowerBlock – it is prepared for that as well.

S1: pin 12
S2: pin 11
5V OUT +: pin 2 and pin 4
5V OUT -: pin 6 and pin 9


			

You need to connect your micro USB cable only to the PowerBlock – and not to the Raspberry Pi directly. Alternatively to the micro USB connector you could also use the 5V and GND input pins for power supply.

To turn the Raspberry Pi on and off with the PowerBlock you need to attach a toggle switch to the two button pins on the PowerBlock. How does the PowerBlock work then? Technically speaking, the microcontroller on the PowerBlock looks, if the two pins of the switch are connected or not. If they are connected, a GPIO pin of the microcontroller on the PowerBlock is pulled to GND and interpreted accordingly.

The PowerBlock has pin outs for an optional status LED that indicates the power state of the Raspberry Pi. You can directly attach an LED to the pins that are marked with “LED”. You need to pay attention to the polarity of the LED: The LED pins are marked with “+” and “-” for that.

The LED will blink in four different patterns that depend on the power state of the Raspberry Pi:

1. Off: The LED is simply off.
2. Booting: The LED slowly fades in and out.
3. On: The LED constantly stays on.
4. Shutting down: The LED fades in and out twice as fast as during boot up.