Open Source Controller and Failsafe Box - progress report

The NoFossil Control System (NFCS) is plodding along on its way to official release. My plan is to offer it several ways:

1) First and foremost, I intend to offer all specifications, design, and software at no cost to anyone who wants to build one or build their own design based on it. That's how I've started and that's how I intend to continue.

2) Second, I intend to offer a DIY kit with all the components at a nominal markup to cover my costs and time.

3) Third, I'd like to offer an assembled and tested version with minimal support if I can find a reasonable cost assembly resource.

4) Finally, I may offer a standard commercial version with commercial level documentation and support intended for professional installers, systems integrators, and so on.

The pictures show prototype #1 part way through assembly and test. It's running in this picture, and the relay is activated (or not) based on the temperature measured by the temp sensor. The baseline configuration is as follows:

- 8 temperature sensor inputs (thermistor, thermocouple, or LM35)
- 32 discrete outputs (can drive relays, LEDs, etc.)
- 32 discrete inputs (can detect switch closure such as thermostat, aquastat, relay, etc.)
- Ethernet interface (wireless optional)
- Data logging
- DC Power supply (computer and relay drive)
- NFCS web-based logic programming
- NFCS web based status and control
- Remote access for service and troubleshooting

And yes, Craig, you can control it from your iPhone ;-)

The bill of material isn't quite complete and doesn't include shipping costs, quantity discounts, and so on. It's shown with a socketed relay on the internal DIN rail that's not included in the BOM. A relay/socket combination is about $8.

Thanks for the feedback and kind comments. My perception is that controls are a barrier to adoption of the kind of wood / solar / storage / fossil systems that we all want to see. I'm hoping this reduces the magnitude of that barrier.

To answer some questions:

It's in a standard NEMA enclosure, and comes with brackets for various mounting options. There's no high voltage in the enclosure, so the normal issues of grounding may not apply. It does have a grounding lug, though.

It's intended to be used with one or more remote relay boxes that handle the high voltage and failsafe functions. I'll post a diagram and photograph when I get a chance.

If anyone wants to build their own, I posted the bill of material. The web programming software is about 75% complete at this time. I'll provide as much support as I can.

I agree that this will need its own forum at some point. I'm really hoping to develop an active user community over time that can contribute both to the functionality of the system as well as helping each other.

As promised earlier, here's a shot of the companion 'failsafe box' along with a schematic and bill of material.

The failsafe box was developed to satisfy two objectives:

1) Failure of the NFCS controller must NOT result in loss of ability to heat the house.
2) High voltage / high current does not belong in the same box as the computer.

The basic idea is that thermostats and zone valves (or circulator relays) are connected to the failsafe box which is in turn connected to the backup heat sources as well as the NFCS controller. The relays are configured so that basic heating functionality continues to work even if the NFCS controller is not connected.

The failsafe box is application specific as far as the number and type of relays. In this example, simple backup thermostats are connected and set to a really low temperature (say 55 degrees). As long as the NFCS controller is connected and active, it will turn zones on and off to maintain the normal desired temperatures as measured by its own temperature sensors. It will also disable the demand signal to the backup heat source as long as there's heat available from the wood boiler or storage.

If the NFCS controller is not connected, then the backup thermostats control the backup heat source.

This is only a sample application - there are lots of ways this could be done.

The cost of the failsafe box is heavily dependent on the number of relays.