Refrigerator control Part 3 #VSCP #IoT #m2m

The refrigerator again. It takes more time then expected of course. It always do. This time because I have a lot of other things to attend to at the moment.  I understand if you ask some questions about this project. So I answer them here (before you actually ask them)

Why this project?

Our refrigerator broke down two weeks ago. And we need one also in my family.  Of course we do, open source programmers may not afford much buying stuff but we also want our milk to be cold.  Luckily it is winter here now and we have some other storage that is at about four/five degrees so it is no immediate panic,  but as weather is getting better (the spring is coming)  this is not a good long-term solution.

When our fridge broke down some years ago I decided to try to rescue it and if it was possible I would take standard VSCP modules to do so.  The compressor was OK and if it is this is a simple  project mostly.  This project has worked perfectly well since then and became a nice VSCP demo project.

Yes, Yes, YES it’s an overkill using VSCP standard modules for this. An Arduino or some other simple board would have done the job. But I wanted to use the modules to see if they did their job also over time. The best way to actually see if things are working the way you thought is to put them in some critical system in your house (the heating in our house is already controlled this way). If there is some bugs or design problems things will be solved by necessity. To have them in a demo system on a workbench is just not the same thing.

So for the refrigerator the first question was to check if the compressor still worked. If it was dead it is just a pieces of junk and not a refrigerator.  But just as with the fridge it was the control logic that had broken also this time. Make me wonder how many perfectly fine refrigerators/fridges are thrown away out there that could have new  control added for a few bucks and do the job they were designed for for many years more.


As with the fridge I decided to go for standard VSCP modules for the refrigerator project to make it a demo project.  It is easier this time as I have the CAN4VSCP bus connected to the fridge that stands next to the refrigerator. I just need to connect the two together.

So I put in a Kelvin NTC10K module and a Bejing I/O module in the refrigerator and hook it up to the CAN4VSCP bus so I am able to monitor temperatures and change temperature settings and get possible alarms from the unit.  As with all VSCP modules they form a self-contained unit.  There is actually no need for a server after they have been configured. The second video here show the configuration process and the first show how the modules are connected together.

The Kelvin NTC 10K module is a module that one can connect a couple of temperature sensors to.  It can be programmed to alarm at low and high temperatures and as in this case turn on and off things when certain temperature thresholds are reached.

In the fridge project a Paris module is used together with the Kelvin NTC module. The Paris module is constructed to control relays and have all the electronics on board to do that. It also include protection timers and a lot more.

In the refrigerator project I decided to use the Beijing module instead of the Paris module. Mostly because it did not matter to have standard I/O channels  as I use a solid state relay to switch on and off the compressor, but my main reason was that  I got a chance to use it in a real life demo system.

So the Kelvin NTC10K module sense the temperature in the refrigerator and the Beijing module is used to switch the compressor on or off and to sense if the refrigerator door is open or not and if it is light the lamp inside the box.

It is possible to  sound s siren if the door to the refrigerator is opened between midnight and six in the morning. But some things just hit you right in the face so I will not implement that functionality. At least not now.


Connect cables and putting it in the refrigerator where the old control logic was located. No programming is needed just configuration.  The second video above show a bit of this configuration but I will go through it in a more precise way in a future post. Hopefully things will work as thy should tomorrow. The VCSP modules are very flexible and can be used in most control situations to form self-contained systems that can be connected together and be connected to the world in a safe and secure way.

#VSCP Register Abstraction Model (VSCP-RAM)

The single most important part of a VSCP system is the Register Abstraction Model.  With it you can describe anything that are real (or even not real) in this universe.  Quite a piece of a powerful super tool to have in your arsenal.

In the IoT world people often say that MQTT,  CoAP,  etc is IoT servers/protocols. For me they are transport mechanisms. Good ones, at least in the case of MQTT.  Useful for IoT? Yes. But IoT severs no?

Now what!?

To explain my point. Look at a web server. It serve content using the HTTP protocol. Simple enough. Works good. Quite similar to MQTT in fact.


this was not the reason the world-wide web was a success.  If everyone started to serve different non standardized content with the http protocol it would have been a mess of it all. Very hard to cope with for the web readers at least.  Yes, it would have been useless. Well this was more or less the case also pre HTML.  But what HTML did was to specify a common format for the content. That was the killer that made everything moving. Not the web server which is just the transport mechanism just as MQTT and others are in IoT.

VSCP try to be more than a transport mechanism for m2m and IoT. A common way to look at and handle “things”.  (yes MQTT can transport it just as CoAP and others can)

In the picture above is a view on how VSCP look at a “thing“.  A “thing“can be a TV,  a refrigerator,  a car,  a lamp,  a human or whatever. Everything can be described in this way. Yes, everything. Hardware as well as software or a some abstract non existing life form. ANYTHING is the world.

To describe anything is of course not a problem. One just describe the anything in a way that comes up in one’s mind. So if we ask 999 people to describe the anything object there will be 999 different descriptions. That is actually OK. The problem is rather that there will be 999 different ways to interpret the descriptions of the anything. Hard work.

If we instead came up with a common way to look at the anything,  an abstraction of it,  we could all use that abstraction to describe every the anything and after that we do not need to come up with so many new ways to interpret the descriptions nor ways to interact with the anythings of the world. We could even use this abstraction on top of any of the 999 description from above as it is useful for describing anything. Good if we love our “description” and don’t want to throw away our lovely description and interpretation of it.

Of course, the abstraction would be most useful if it was available for a high-end system or user as well as for low-end system or user.  Low end can actually be really  low-end.  So we better start there.  But a high-end user or system demands handling of great complex things so we need to take this into account as well.

VSCP solve this in the following way

  • Everything can be described by a collection of  8-bit registers.
  • To know whats inside an 8-bit register you need the ability to read it.
  • To change the content of an 8-bit register you need the ability to write it.

So VSCP can describe everything in the universe,  yes everything from a flower,  a person,  a car or anything else with a set of 8-bit registers. The only thing needed to interact with the resister set is that registers can be read and written.


  • Read a byte.
  • Write a byte.

is all that is needed for  VSCP to work with “anything” on its lowest level.

In VSCP this is called the Register Abstraction Model.

VSCP’s register abstraction model demands that all “anything” objects have a set of registers that contain specific information. Same on all. The two most important parts is GUID, ett globally unique id  a 16 byte world unique if for “the anything“,  and a 32-byte area which contains a pointer to a  Module Description File.  The GUID identifies “the anything” much the same way as an Ethernet MAC does for Ethernet device.  They can actually be coupled. The MDF pointer can point at a local location or to a file on the Internet. The content is a well-defined XML description of “the anything”.

One thing that is described is of course the registers of “the anything“.  But to handle things on a register level can be to hard sometimes. For instance is a floating point value stored in eight registers. If this floating point value for instance represent a temperature of “the anything”  and this is what the application or user is interested in there should be no need to know how it is actually stored on “the anything“.

So to make life easier for high-end systems or users the MDF often also contains abstractions. Abstractions specify higher end type such as strings, floats, integers, booleans and tell in what registers they are stored and also how many bytes they use.  So a high en user just handle these higher end objects, reading and writing them,  even if the system still only read and write bytes.

Both registers and abstractions describe the same “anything“,  just on different levels.

At this point it would be possible to build an application that can configure any device, “anything“,  just by read/write byte operations and by reading and interpreting the MDF of the unit. The user (or machine) just fill in the values. The same application can be used to configure a car,  a TV,  a clock radio etc.

The MDF can also contain wizards. A wizard can guide a human user, step by step through a specific setup of a device. They are also described in an abstract way and can be interpreted by C/C++, JavaScript and other higher end programing languages alike.  So it is as easy to make an app. that goes through the wizard steps as it is to make an HTML page that do the same.

It is of course possible to use XML/JSON on the higher level to “set register/abstractions”.  A read and a write byte operation is still all that is needed.

The fact is that the register abstraction model is so light weight that it easily can live alongside a more proprietary solution

But way?

That you have to think about yourself… ,-)

ps VSCP is of course a lot more than this. There are events, classes/types, bootloaders, decision matrices and a lot of other clever things. ds.

IoT, M2M and VSCP talk from Grodans Paradis AB

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