PWM

For an upcoming modification to the central heating I need a controller capable of outputting a (standard?) 0 to 10V control signal.

Of course, this is a job for Arduino/Jeenode, and not for some store bough industrial controller.

Since the JeeNode works at 3.3 volts,  I set off to build an amplifier, using an LM358, wired to multiply the input by 3 times, which gives a nice and convenient range of 0 to 10V!

I am still in the process of building the circuit, but for this I needed to get the oscilloscope out.

Once I had the work on the breadboard ready I captured the following images, I thought they were nice.

I wanted to have both lines in the same shot, but my channel B is not working well, so I can only use one channel of the scope.

After I shot these, I proceeded to blow up an LM7805 (why does it have a different pinout from the LM78L12) and consequently blow up my old trusty JeeUSB version 2...I hope I can bring it back to life.

Just a short mention of what the project comprises: 0..10V controller for a 24V ventilator fan, and two Dallas 1820 measuring the temperature of the water flow (in and out). The motor will be controlled based on these.
Soon the circuits and protoboard pictures, later custom PCB's?

More OpenTherm

Back from holidays! and with good news - I managed to communicate with the boiler using OpenTherm!

If you remember, the last time I managed to communicate, however, the boiler was not doing what I was telling it to do, namely, to heat up the central heating water to 35 degrees, instead, it was displaying an error state, and not a very informative one, in the small display.

Here is a picture showing the oscilloscope trace, where both the master to slave and slave to master burst messages are visible.

Since I had not implemented a decoder for OpenTherm, to analyse the reply from the boiler, I could not know what the boiler was complaining about. So I came up with a solution: I installed the OpenTherm arduino decoder found in the palebluedot site, and commented my emitter directly to the arduino with the decoder. As expected, the message was going with an data error. After finding a couple of bugs in my manchester encoder, I managed to get a correct message across.

Time to send the message to the boiler.

Another trip to the attic, and the boiler received the message, but didn't start heating up, but also no longer went into the error state. A careful read of the protocol, and I realised that I was disabling the CH when sending the message with ID=0. At the end of page 24, one can read that the "CHenable bit has priority over the Control Setpoint". So, another change to the message, another trip to the attic, and success!! The boiler started up, heating up the central heating water to the set temperature of 35 degrees!!

Next step is to implement the decoder in the same JeeNode, and the make a little PCB shield. After that, it is a matter of software, both in the JeeNode and in the server, to implement the communication layers, and of course, the much awaited and though of PID controller!

Tektronics 453

Just got an old Tektronics 453 Oscilloscope that was going to go in the garbage!! Looks great and it works! which is the most important part! now I can finally check the hall effect sensor I got in Taiwan when near the water meter to see if I can detect the parts rotating inside the meter. At this moment the signal is smaller than what the Arduino can detect, and I would like to see the signal before starting to build an amplifier - also to know how much amplification does it need!


It came with 2 probes, nice old ones, one from Phillips and one from Tektronics! I think there are some more goodies where this one came from (my wife got it for me from the lab at her work), but I don't know what they are yet (my wife has no idea what these things are, or what they are for!)
Out to try out my new toy now!!