How to develop a device based on wireless modules
Table of contents
1 Why to write the IoT / M2M Cookbook? 5
2 Fundamental considerations before starting the IoT / M2M project 5
3 Certifications and approvals 6
3.1 Examples for Radio approvals in EU and US 6
3.2 Examples for Radio approvals in US 7
3.3 Examples for automotive related approvals in EU 7
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 (14.04.11) 14
5.2 Cellular module in power save mode (14.01.11) 14
5.3 Internal resistance of batteries and linear voltage transformers 14
5.4 Switched mode voltage regulator 16
5.5 Capacitors at power supply and cellular module (14.04.11) 16
5.6 Supply voltage for GNSS antenna (14.04.11) 16
6 Antennas for IoT / M2M devices 16
6.1 Monopole and dipole antennas 17
6.2 Nothing will interfere with your embedded antenna? 17
6.3 Why the embedded chip or patch antennas are resonant on the frequency? 18
6.4 How will the ground plane affect your embedded antenna? 18
6.5 How to connect your embedded antenna with your wireless module? 20
6.6 How to design an antenna matching circuit? 21
6.7 Free of charge software to generate a matching circuit automatically 22
6.8 How to switch between an internal and external cellular or GNSS antenna cheap? 22
6.9 Which GPS antenna shall be used for a tracking device? 23
6.10 Which embedded antenna to select for a Bluetooth / GNSS application? 24
6.11 Dos and don’ts during embedded antenna design 25
6.12 Example: Embedded PCB antenna inside a vending machine of NeoNumus 26
6.13 Example: Embedded antennas at Telematic device IN1 of GPSoverIP 28
7 Simulation of an embedded GSM PCB track antenna 28
7.1 Definition of the antenna simulation project 28
7.2 Description of the inverted F antenna 29
7.3 3D model of the simulation 30
7.4 Optimization – determination of antenna shape 31
7.5 Typical requirements of a quad band GSM antenna 31
7.6 Optimization of the quad band antenna GSM antenna shape 34
7.7 Directional characteristics of the antenna for two GSM frequencies 35
7.8 Influence on the antenna characteristics of the housing 37
7.9 Influence of the ground plane on the antenna characteristics 38
7.10 Optimisation of the simulated antenna with matching circuit (03.05.2014) 38
8 Components around the cellular module 39
8.1 SIM card 39
8.2 SIM card subscription 40
8.3 Low ESR capacitor 40
8.4 ESD protection and shielding (14.04.11) 41
8.5 Loudspeaker and microphone (14.04.11) 41
8.6 Firmware update at final PCB 42
9 Examples for mistakes and errors during M2M development 42
9.1 Power down reset 42
9.2 SMS errors 42
9.3 CSD errors 43
9.4 IP connection errors 43
9.5 Analysing of a maximum of design mistakes in one M2M design 43
9.6 Analysing of mistakes at PCB track antenna for GSM 44
9.7 Analysing of GSM chip antenna on small ground plane 45
9.8 Analysing of a Swiss GSM watch 46
9.9 Analysing of embedded LTE antenna in detail (27.04.2014) 47
10 Testing your M2M device 48
10.1 Emulation of TX power peaks 48
10.2 TX power peaks by cellular module test mode 48
10.3 TX power peaks by GSM tester 48
10.4 Testing of the sensitivity 48
10.5 Testing of the radiated TX power 48
10.6 Where to get a cellular tester cheap? 49
10.7 Testing the GNSS module 49
10.8 Measurement of the cellular antenna in 3D 49
10.9 Summary of testing 49
11 AT Commands 50
11.1 AT commands during power on your cellular module evaluation kit 50
11.2 AT commands to send a SMS 51
11.3 AT commands and logic loops for set up a communication channel 51
12 Nice tools to make the IoT / M2M development easier (27.04.2014) 52
13 Thank you 53
1 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. We developed Machine to Machine devices without to know that these devices will be decades later called M2M devices. 25 years ago there was no GSM for data communication. The first steps in wireless data communication I made with FSK on Private Mobile Radios. 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 networks with FSK data communication. Years ago the last public analogue trunked radio network in Germany was taken out of service. GSM jumped in with its Short Message Service and Circuit Switched Data. CSD offered us already 9600 bit per second. Nevertheless, SMS and CSD we could use for countywide communication easy and with roaming worldwide data communication came true. 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 anymore. Some people try to split in M2M and IoT. IoT or M2M – it does not matter, both often use the same wireless link.
The IoT / M2M Cookbook describes how to develop a tracking device based on cellular and GNSS modules. A telemetric M2M device you get by ignoring the GNSS part.
Sometimes it is not easy to use the 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. If I use the word GSM module, then this covers 3G and 4G modules as well, because the fallback of UMTS, HSPA and LTE is still 2G (GSM/GPRS). GPS is already the wrong word. GPS is just one out of several Global Navigation Satellite Systems. Today we can access to the Russian GNSS called Glonass as well. 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. The book is 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. 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.
I hope you will enjoin it 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
Thanks
Awesome! Great work Harald. you just fired up my unending passion for telecommunication sir. i look forward to reading all your works in the comunication industry. many thanks
Zion, thank you for your kind words. I have only given back what I have received about 25 years ago. 25 years ago, my boss transferred a lot of knowledge to me. Today I do the same and use thereto the Internet. The Internet makes it possible to spread knowledge worldwide.
Thanks very much for share your knowledge with us.
I think that low price technologies such as sms/ussd , can be used in africa/asia/southamerica to organize/help people , I know that actually is already used , but not in a massive scale yet.
Governments should be more proactive with the support of “developed” countries. Vielen Dank
Leo, USSD in in Africa much more popular than here in Europe. Nevertheless the vending project in listed in IoT M2M Cookbook is based on USSD as well. The GSM / GPS tracker for birds also. The reason to select USSD was not the price. For the vending application it was the speed. Within 2 seconds the toilet door is open and your SIM card will be charged. For the bird tracker the reason was power consumption. USSD is much faster travelling than SMS or even GPRS. A wake up to transmit an USSD, wait for incoming USSD and go to sleep is possible in a very short time. Time means power consumption and discharge of the battery.
Inside the book a PCB GSM antenna is described well. Developers that will make a copy can save the money to order an antenna. Even the GPS antenna can be designed as a PCB track. This will be the next cost saving. And if people ask friendly for sources of inexpensive wireless modules, then I can help as well.