IoT M2M blog

The home of free hints and tips about wireless IoT / M2M

IoT M2M Cookbook

How to develop a device based on Wireless Wide Area Network modules

Table of contents
1 Why to write the IoT / M2M Cookbook?    5
2 Fundamental considerations before starting the IoT / M2M project    6
3 Certifications and approvals    6
3.1 Examples for Radio approvals in EU and US    6
3.2 Examples for Radio approvals in US and Canada (PTCRB)    7
3.3 Examples for automotive related approvals in Europe    8
3.4 SAR – Specific Absorption Rate    8
4 Cellular data communication (GPRS, USSD, SMS, CSD, DTMF)    9
4.1 Voice communication    9
4.2 Modem / acoustic coupler / encryption    9
4.3 DTMF (Dual Tone Multi Frequency)    10
4.4 GPRS (General Packed Radio Service)    10
4.5 SMS    11
4.6 USSD (Unstructured Supplementary Service Data)    11
4.7 Comparison of power consumption (SMS, USSD and GPRS)    12
4.8 CSD (Circuit Switched Data)    13
5 Supply voltage    13
5.1 Power on timing and waiting    14
5.2 Cellular module in power save mode   14
5.3 Internal resistance of batteries and linear voltage transformers    14
5.4 Switched mode voltage regulator    16
5.5 Simulation of a switched power supplies with LT Spice    16
5.6 Capacitors at power supply and cellular module    18
5.7 Supply voltage for GNSS antenna    18
6 Antennas for IoT / M2M devices    18
6.1 Monopole and dipole antennas    18
6.2 Nothing will interfere with your embedded antenna?    19
6.3 Why the embedded chip or patch antennas are resonant on the frequency?    20
6.4 How will the ground plane affect your embedded antenna?    20
6.5 How to connect your embedded antenna with your wireless module 04.11.2014    22
6.6 How to design an antenna matching circuit    24
6.7 Free of charge software to generate a matching circuit automatically    25
6.8 How to switch between an internal and external cellular or GNSS antenna cheap?    25
6.9 Which GPS antenna shall be used for a tracking device?    26
6.10 Which embedded antenna to select for a Bluetooth / GNSS application?    27
6.11 Dos and don’ts during embedded antenna design    29
6.12 Example: Embedded PCB antenna inside a vending machine of NeoNumus    30
6.13 Example: Embedded antennas at Telematic device IN1 of GPSoverIP    31
7 Simulation of an embedded GSM PCB track antenna    31
7.1 Definition of the antenna simulation project    31
7.2 Description of the inverted F antenna    32
7.3 3D model of the simulation    33
7.4 Optimization – determination of antenna shape    34
7.5 Typical requirements of a quad band GSM antenna    34
7.6 Optimization of the quad band antenna GSM antenna shape    37
7.7 Directional characteristics of the antenna for two GSM frequencies    38
7.8 Influence on the antenna characteristics of the housing    40
7.9 Influence of the ground plane on the antenna characteristics    41
7.10 Optimisation of the simulated antenna with matching circuit    42
7.11 Design in of the simulated antenna to special GSM / GPS tracker    43
8 Components around the cellular module    44
8.1 SIM card    44
8.2 SIM card subscription    45
8.3 Low ESR capacitor    45
8.4 ESD protection    46
8.5 Loudspeaker and microphone    46
8.6 Firmware update at final PCB    46
9 Examples for mistakes and errors during M2M development    46
9.1 Power down reset    46
9.2 SMS errors    47
9.3 CSD errors    47
9.4 IP connection errors    48
9.5 Analysing of a maximum of design mistakes in one M2M design    48
9.6 Analysing of mistakes at PCB track antenna for GSM    49
9.7 Analysing of GSM chip antenna on small ground plane    50
9.8 Analysing of a Swiss GSM watch    51
9.9 Analysing of embedded LTE antenna in detail     51
10 Radiation noise, maximum spurious, antenna radiation    52
10.1 Antenna radiation versus radiation noise    52
10.2 Conductive noise    54
10.3 Conductive noise transformed to radiated noise    54
10.4 Radiated noise transformed to conductive noise    54
10.5 Prevention against radiated noise    55
11 Quick Start Guide Vector Analyser MiniVNA Tiny    56
11.1 Explanation S11, VSWR, return loss, reflection coefficient and antenna bandwidth    58
11.2 Unearth the truth – four cellular antennas tested with MiniVNA    60
12 Testing your M2M device    66
12.1 TX power peaks by cellular module test mode    66
12.2 Pseudo load of 2 Ampere peak load with self-made function generator     66
12.2.1 Schematic diagram of the self-made function generator    67
12.2.2 Pseudo load with 2 Ampere peak by standard function generator    67
12.3 TX power peaks by GSM tester    68
12.4 Testing of the sensitivity    68
12.5 Testing of the radiated TX power    68
12.6 Where to get a cheap cellular tester?    68
12.7 Example of a measurement report by GSM test equipment    68
12.8 Example of a measurement report by GSM test equipment    73
12.9 How to test an UMTS module on foreign band    74
12.10 Test with UMTS testers    74
12.10.1 Tests without UMTS tester    75
12.11 How to test an LTE module on foreign bands    75
12.12 Expected trouble with LTE modules worldwide    75
12.13 Testing the GNSS module    76
12.14 Measurement of the cellular antenna in 3D    77
12.15 Summary of testing    77
13 AT Commands    77
13.1 AT commands during power on your cellular module evaluation kit    77
13.2 Hello World in GSM – AT commands to send a SMS    79
13.3 AT commands and logic loops for set up a communication channel    79
14 Project descriptions of IoT M2M devices 81
14.1 Project description of a long-term tracking device    81
14.2 Project description of a bendable tracking device of bank notes    82
15 Thank you    84

Why to write the IoT / M2M Cookbook?
Since more than a century quarter I am in Wireless M2M. 25 years ago we had no word for M2M or  IoT. We developed Machine to Machine devices without to know that these devices will decades later called M2M devices. 25 years ago there was no GSM network for wireless data communication. The first steps in wireless data communication I made with Frequency Shift Keying (FSK) on Private Mobile Radios (PMR). On PMR we reached a communication speed of 3600 bit per second. A while later we got public analogue trunked radios. These trunked radio systems offered local terrestrial wireless networks on FSK. Years ago the last public analogue trunked radio network in Germany was taken out of service. GSM jumped in with its Short Message Service (SMS) and Circuit Switched Data (CSD). CSD offered us already 9600 bit per second. Nevertheless, SMS and CSD we could use for countrywide data communication easy. On top we got by roaming worldwide data communication. And today GSM/GPRS is phasing out step by step and will be replaced to 3G and 4G technology.
In US the cellular operator AT&T does not accept new M2M applications on GSM/GPRS any more. Some people try to split in M2M and IoT. IoT or M2M – it does not matter, applications for IoT or M2M often use the same wireless technology. IoT is the umbrella for a number of subsets in wireless data communication. M2M is one out of this subsets and maybe it is one of the oldest subsets as well.
This IoT / M2M Cookbook describe how to develop a tracking device based on cellular and GNSS modules. A telemetric device you get by ignoring the GNSS part. A typical device without GNSS is for example a cellular router with Ethernet ports or a cellular to Wi-Fi bridge. Nevertheless the navigation system for trucks described in this book is using already six different wireless technologies (2G, 3G, GNSS, Classic Bluetooth, Bluetooth Low Energy and NFC) with five different antennas in one enclosure.
Cellular networks for GSM, HSPA and LTE are the regular Wireless Wide Area Networks (WWAN). However, in some regions we have WWAN on CDMA and WiMax.
Sometimes it is not easy to use the right words in English language. The common word for SMS in UK is “text message”. In this book it will be still named SMS. A prepaid SIM card in UK they call a “Pay as you go SIM card”. I will mainly use the common words specified by ETSI – I will call it prepaid SIM card. If I use the word GSM module, then this covers 3G and 4G modules as well, because the fall-back of UMTS, HSPA and LTE is still 2G (GSM/GPRS). GPS is today already the wrong word. GPS is just one out of several Global Navigation Satellite Systems (GNSS). Today we can access to the Russian GNSS called Glonass as well. And the Chinese GNSS is called Beidou. And sooner or later we will get access to the European GNSS called Galileo.
The IoT / M2M Cookbook shall help developers of wireless application to save some time and maybe inspire some ideas. It is a book for makers and just the summary of experience collected in my different jobs. By leading a team of developers with the order to design a mobile GSM/GPS tracking device I learned to think like a developer of an IoT / M2M device. In my more than 15 years working with a manufacturer and in distribution I gave the same hints and recommendations to developers of wireless applications again and again. The starting point for the book was an application note with 14 pages written in July 2010. In May 2012 I made the decision to write the story that I have to tell weekly to customers in a book. The target is to guideline developers from the idea for an IoT / M2M device to a final product with mass production. The book will not tell you how an inverted F antenna is working. To explain this I will use links to files that tell the details. Anyhow the book will tell you facts that are often missed in the official documentation of manufacturers of radio modules and antennas. It also shows an inverted F PCB antenna for GSM in details, explains how to redesign it to an own PCB up to encapsulation the whole design in epoxy resin. It also explains how to integrate a chip or PCB antenna with coaxial cable.
Some power supply concepts including LT Spice modules for DC/DC regulators and load generator for the 2 Ampere peak currents are a part of the book too.  Be aware, that the power down reset is still the main fault in designs with cellular modules.
I hope you will enjoin the reading of the book  and I hope it will save some of your time as well.

If you an interest to read the IoT / M2M Cookbook then do not hesitate to drop an email to harald.naumann (at) gsm-modem.de

59 Comments

Add a Comment
  1. Hello Harald

    I am interested in your book, how do i proceed to get access it.

    Thanks
    Gordon

  2. Hi Harald,
    I am interested in your book. How do I download it? Thanks
    BJ Raval

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  5. Hi ,

    I am interested in ordering a pdf copy of your book.
    Please advice me the next step.

    Thank you .

  6. Welson, you get a link and password after placing an order and money on my account. You can pay by Paypal, debiting of your credit card by Paypal or wiring to my bank account.

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