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3pi Expansion Kit without Cutouts - Black

Pololu item #: 978

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This kit gives you everything you need to add a second level to your 3pi robot. In this version, the LCD pins are brought up to the expansion board from the base via extended headers for your own custom use. This black printed circuit board matches the color of the 3pi and can also serve as a general-purpose round prototyping board.

Compare all products in Robot Kits or Robot Kits with Soldering or Prototyping PCBs.

	Description		Specifications (0)		Pictures (6)		Resources (1)		FAQs (2)

Can I augment my 3pi by adding my own electronics/sensors?

Yes. The easiest way to augment your 3pi is through an expansion kit, which can comes either with cutouts that let you see the LCD below or without cutouts. The version without cutouts replaces the LCD, giving you access to more I/O lines and more prototyping space. An expansion kit is not required for addition of your own electronics, however.

The 3pi robot has a limited number of free I/O lines that can be used as inputs for additional sensors or to control additional electronics such as LEDs or servos. These free I/O lines can be accessed through the pads at the center of the 3pi, between the two motors, labeled PD0, PD1, ADC6, ADC7, and PC5.

PD0 and PD1 are unused digital I/Os, and connect to the ATmega168’s UART module if that module is enabled. This means you can freely use PD0 and PD1 for general-purpose digital I/O, or you can use them for serial communication with another microcontroller, a serially-controlled device, or a computer (note that you will need to convert the signal to RS-232 levels or USB to communicate with a computer).

PC5, ADC6, and ADC7 are all connected to 3pi hardware via removable shorting blocks. By removing the shorting block, you can use these pins for your own electronics. PC5 can be used as either a digital I/O or an analog input. When its shorting block is in place, it controls the emitters for the IR sensors; when its shorting block is removed, the emitters are always on.

ADC6 and ADC7 are dedicated analog inputs. ADC6 connects to a voltage divider circuit that monitors the battery voltage when its shorting block is in place. ADC7 connects to the user trimmer potentiometer when its shorting block is in place.

Please see the 3pi pin assignment table for more information.

I’m adding peripherals to the 3pi that require 5 V. How much current can the 5 V (Vcc) power bus supply?

Because the 5 V goes through two power stages, the answer is not completely clear-cut. The 5 V regulator itself has a 900 mW power dissipation limit, so with a 4.3 V drop from the 9.3 V boost voltage to 5 V, we get just over 200 mA. The stock electronics on the 3pi typically use under 50 mA (however, this depends on what your program is doing, if you are making high-frequency noise with the buzzer, and so on), so you could figure an absolute max of 150 mA, with 100 mA being a more comfortable guideline.

However, the boost voltage has a limit of its own of around 1 A, which is dependent on your battery voltage. The motors and IR LEDs also use this supply, so using a lot for your 5 V will affect what is available for the motors. You can almost stall the motors and still have the full boost voltage on the motors in the stock configuration; if you’re also drawing an extra 200 mA for other electronics, the boost voltage will start dropping as the motors approach stall, though this is not necessarily a bad thing since it will limit the stress on the motors and lower the voltage drop on the linear regulator.