Review of Mamba shield for Arduino Uno

Review of Mamba shield for Arduino Uno

ABSTRACT

This document analyzes the Mamba shield for Arduino with several experiments of powerlines communications over DC lines and AC lines. Principally, I’ve tried to guess the baud rate that this product can reach without transmission errors. INTRODUCTION

Power line communications technology is a way of carrying data on a conductor that can also be used for power transmission. You can use it to pass a control signal through the electrical wiring in a house for home automation. LinkSprite's Mamba shield gives your Arduino this ability. This Narrowband Powerline Communication shield can be controlled by your Arduino board using a simple SPI interface. From these places you can download the electric schematic, the codes and a step-by-step guide. The board needs to supply at least 1 Amp to work correctly. One of his inconvenient is that it needs a lot of caution if you use the board with high voltage. 

The main element of Mamba shield is the PLM-1 modem. That chip is the brain of the board. It is a fully digital data transceiver for powerline communications using Frequency-Shift Keying (FSK) and it is designed to be controlled from an external Central Processing Unit, most commonly a microcontroller (MCU). Implementing the PHY and MAC layers of the OSI model, the PLM-1 provides a way to efficiently modulate and demodulate data packets. It features collision detection, as well as automatic forward error correction and CRC-16 data integrity verification. For more information, you can read the AC-PLM User manual that it can be downloaded from [3]. After this brief introduction, I explain the tests with this Arduino Shield.

TEST 1: MAMBAS CONNECTED DIRECTLY THEMSELVES 
This test consists in sending messages from one PLC emitter to the PLC receiver. The received messages should not have any error. The PLCs are united by couples of wires which they have not an extra direct current, only the signal transmitted by the PLCs. The size of the message, the speed transmission, the loss packet rate and the length of the wires will change for watching the differences of loss packets in the transmissions. The Arduino are powered by the USB connected to the PC. The picture below shows the two Arduino connected directly.

This test is for seeing the change of the quantity of loss packet with different baud rates. The transmission code is running always and the loops are separated by a delay of milliseconds. The baud rate will be faster if the delay is less. The codes of the two Arduino with the Mamba shield are provided at the end of this review. The Appendix1has the transmiter code and the Appendix 2 has the receceiver code.

After a study of the code, I’ve reached to the conclusion that the maximum size of the data in a packet is 61 bytes. In each transmission the packet has 3 bytes of header and end of packet that they are configured by the protocol transmission of the Mamba Library. The total size of a packet in a transmission is 64 bytes. The structure of a packet is resumed below.
5 bits 1 byte (0-255) 61 bytes 4 bits (CRC16)
Table 1: Structure of a packet.

The next tables show the relations among the loss packet rate with different delays, size of packet and length of the wires. I’ve selected these delays because they are the points where the loss packet changes in the communications. The Table 2 shows the results with wires of 30 cm and the second Table 3 with wires of 250 cm. The column of characters means the number of bytes of a message without header and end of packets. The size of packet has influence in the loss packet rate.

Mamba Shield connected by wires of 30cm
61 Characters (The maximum) 32 Characters 5 Characters
Delay (ms) Loss packet rate (%) Delay (ms) Loss packet rate (%) Delay (ms) Loss packet rate (%)
260 0 165 0 65 0
257 10 160 10 63 25
256 20 159 25 60 33
255 33 158 33 50 50
250 50 100 50 20 72
100 60 70 60 10 85
50 82 50 75 0 96
20 92 20 88
10 98 10 93
0 99 0 99

Table 2: Relations among loss packets rate, delays and size of packets with wire of 30 cm.


The data of the Table 2 are plotted in the graph below:

Now, the results of the same test with wires of 250 cm of length are in the Table 3.

Mamba Shields connected by wires of 250cm
61 Characters (The maximum) 32 Characters 5 Characters
Delay (ms) Loss packet rate (%) Delay (ms) Loss packet rate (%) Delay (ms) Loss packet rate (%)
250 0 170 0 65 0
248 12 160 10 60 10
244 33 158 33 59 25
240 50 150 50 58 33
120 60 80 54 55 50
80 75 78 60 30 55
50 80 50 75 20 69
30 89 30 84 15 76
10 95 10 87 10 84
0 99 0 99 0 99


Table 3: Relations among loss packets rate, delays and size of packets with wire of 250 cm. 

The data of the Table 3 are plotted in graph below:

The picture of the second experiment with wires of 250cm is shown beneath.

The conclusions of this test are these:

-The number of bytes in a packet transmitted has influence in the Speed Transmission Rate because with less number of bytes, the loss packet is less, hence, the delay in the transmitter code can be smaller.

-The length (short distances) of the wire has not influence in the Speed Transmission Rate because the loss packets are similar with wires of 30 cm and 250 cm.

APPENDIX 1

Example code: