TakkStrip Basics

Introduction

The aim of this tutorial is to introduce TakkStrip, and how to use it.
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TakkStrip_WithRubber.JPG

Overview

TakkStrip is an array of five sensors which were organized into a strip. The distance between the sensors is 8mm.

Tutorial_TakkStrip_Size.JPG

Each strip has a dedicated microcontroller (attiny) which makes it possible to activate required sensor (i.e. chip select).

Tutorial_TakkStrip.JPG

Though the sensors were organized into a strip, the strip can be cut and the sensors can be used as individual units. Cutting space has been indicated between the sensors. Once a sensor been separated, side holes can be used for wiring. The hole size is 0.7mm and was designed for 30G wire.

Tutorial_TakkStrip_Sensor.JPG

Individual sensors can be wired back to he microcontroller through the "optional wiring" connectors.

Tutorial_TakkStrip_Connections.jpg

Power

The strip is designed to work with voltages from 3.3 to 5V

Wiring Up

Four wires are required to operate TakkStrip.
It is suggested using 30G size wire, as these match the holes designed.

The wiring is as following:
Marking Meaning Color Convention
(V) Voltage (5V) Red wire
(G) Ground Black wire
(D) Data White wire
(C) Clock Blue wire

There are many connection holes provided on the strip. These all were provided to expand design flexibility. One of the possible connections is at the side of the strip, as is shown here:

TakkStip_Wiring.JPG

Communication

The TakkStrip uses I2C interface for communication.

A number of approaches can be used to communicate with the TakkStrip:

TakkFast USB Interface - provides high-speed data at approximately 100Hz to a Linux host, and interfaces to ROS drivers. The tutorial for the interface is here, and the tutorial for ROS drivers is here

Arduino - provides a simple interface that is compatible across operating systems and communicates over serial via a virtual COM port that can be read from Matlab, Python, etc. The tutorial is here

I2C-USB bridge from Cypress Semiconductor Corporation. This is a windows-only interface but provides some additional debugging features and includes plotting tools. The tutorial is here

I2C Addressing

To enable fast sampling rates of the pressure sensors a custom I2C protocol was developed. This protocol leverages the addressing bits to select which sensor to sample. This way only the address command shall be sent by the I2C master over the communication lines to select or deselect a pressure sensor.

The microcontroller on the strip is using 8bit addressing. The upper 4bits are used to identify the strip number, and the lower 4bits are reserved for commands.

Three dedicated pins were provided on the TakkStrip to configure the four address bits. These pins are A0, A1 and A2. The address is set during the boot up of the microcontroller.

TakkStrip_Addressing_small.JPG

The address corresponds to the following table:

# A2 A1 A0 Address (Hex)
1 - - - 0x
2 - - X 1x
3 - X - 2x
4 - X X 3x
5 X - - 4x
6 X - X 5x
7 X X - 6x
8 X X X 7x

Note: early versions of the TakkStrip had resolved with a less intuitive addressing pattern. The earlier pattern is archived here.

Commands

Pressure sensors are selected by configuring the lower bits of the address.
Even numbers are for swtching ON the sensors.
Odd numbers are for switching OFF the sensors.

Sensor 1 2 3 4 5
ON x0 x2 x4 x6 x8
OFF x1 x3 x5 x7 x9
* where x is the TakkStrip address.

For example;
Switching ON the first sensor of the TakkStrip with address 6x the master will need to send 60.
Switching OFF the first sensor, the mater will need to send 61.

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