It works! Opentherm Interface V2

We're Back after a very long break!

Last January I presented a schematic for a second version of Alex's JeeTherm to Opentherm interface.

 

Well Alex finally had the time to test it and it works.... almost :-)
The first part of the board related to the physical interface actually works (!) i.e. sending and receiving the bits and packets to the boiler. This part was done with good old technology and using an operational amplifier as an active load.

The second part of the board was designed to power the remote controller from the loop power supply. This one we knew it would be trickier.
Placing the small supercap (0.1F) as load of the regulator was a good idea as the regulator is output short circuit protected so charging current is maintained within reasonable levels. Our fear was that due to the big charge current for some time on power up, the boiler would give up communicating (part of Opentherm interface, in case a boiler is connected to a plain old thermostat).
The key problem was that the display, the backlight (even when disabled) and the Jeenode take too much current for the system to be reliably powered...
We will have to arrange a winter sunday meet to fully debug these problems...

Mini85v2

And now for something completely different, not only do I take an enormous amount of time to do something, I also overrun myself with different projects...

After a year or so of designing PCBs and sending them for fabrication, I finally decided to go for the big one and design a full Eurocard (160x100mm) computer. I have enough confidence on my EDA package (gEDA) and myself to design it, and the prices are also relatively low for a double sided board so I'm jumping to it.

When I dismantled the breadboard mini85 I promised to do a PCB version (this was in 2008!), so here I am back on it 4 years and 2 kids later!
The idea is about the same, build a minimally usable CP/M system on a eurocard, with standard TTL logic circuits, minimum I/O, a switching power supply for the computer and the drive, which is a 3.5inch floppy on top using the high density (1.44Mb).


I've been scaling down from the initial idea of having 512k of SRAM and a paging arrangement and a 8256AH as a UART and parallel port (like my 68k project... that, by the way, is also on hold...), and slowly going back to the simple original Mini85.

I even had a port for system configuration and dip switches, but this version (below) no longer has a MMU.

I think that I am finally setting for a 8085 at 8Mhz connected to a upd765 and a software UART with SID, SOD and RST5.5 lines, memory will probably be 64K SRAM (w/ 32K paged in/out) and a 32k ROM. An ON/OFF switch, a RESET, a TRAP and a RST7.5 interrupt push switches.

FireFly Jam Jar (2)

After a mostly uneventful February, except for the smell of winter we had with week below -5C and snow (2 hours, but just enough to spread havoc in the Dutch transport system), I finally decided to post something.
My FireFly hardware is finished, including the bricolage of painting the glass. I mixed a part of pebeo vitrea 160 frosted medium with yellow colour of the same line. The LEDs are in yellow and orange so a similar colour to enhance the effect seemed appropriate. I used a sponge to enhance the frosted glass, I didn't want Luísa to see the electronics inside (it kind loses the magic). This is how it looks after baking.


On the top I placed one of my solarbotics SCC3733, I opened two holes in the top and fixed the solar panel with two part epoxy glue, I then scraped the epoxy until I found the contacts and connected the board.


It doesn't really look that good, the photo is over exposed and you can't really see the mess I've made... not only the two components were not thoroughly mixed, there are lots of air bubbles in the resin.

Finally I also glued the board to the top of the jar.


You can just see the drill under the board and the wire connecting the solar panel to the battery charger. The jumper powers just the circuit but leaves the battery charger charging.

Now it is just software, the current code is running from the Reindeer Christmas Ball so battery runs out... fast...
I just checked my first post on this project was here, 5 months ago... I'm very slow... very very slow...
The idea of having it with the solar panel is to teach Luísa that the "FireFlies" need to be fed (i.e. put on the sun)... the solar panel is also a way to turn it on/off.

OpenTherm v2 First Prototype

I finaly built a prototype of the opentherm interface (version 2) for Alex to test, since he dosen't have all the tools to test it I'm hoping that at least the physical interface works, the other features are powered through the interface and using a supercapacitor to hold the power during radio transmission.



The board has a JeeNode interface so Alex doesn't have to change much, there are two extra jumpers, one connects the opentherm rectified voltage to the PWR input of the jeenode, and the other connects the 3.3V output of the jeenode to a supercap. It is still a bit oversized but... Well it is a prototype... The OpAmp is the LM358 (dual version of the quad LM324), works from 3V to 33V and it is relatively low power. The specification of Opentherm states a open voltage of 40V so I had to protect the OpAmp with a parallel Zener (seen in the picture).


A lot has to be done on the jeenode side, but it is mostly software regarding the power saving modes and saving enough power before the short bursts of radio transmission. The schematics of this circuit is based on the published before, but I'll hold the final one until Alex gives me feedback.