DELARANEWS

Craig

Craig Miller, W8CR

I have flu fever

Quick recap: Chimney fire almost burned the house down, replaced chimney, installed thermocouples in flues, plan to use Raspberry Pi to read thermocouples. Done. OK, the last we left this, Santa did deliver two Raspberry Pi “HATS” that allow one to connect up to 8 thermocouples. Way to go, Santa! Like a little boy on Christmas morning, I spent several hours figuring out how to install the hats and wire up the thermocouples. The hat manufacturer, Measurement Computing, supplied a nice set of libraries and sample code, online, to get me up and running in short order. I plugged in one board on the Pi. twisted together a short length of thermocouple wire and connected to one of the four terminals. They support two languages to talk to the hats, C++ and Python. It’s been years since I did any C and C++ programming and didn’t know anything about Python. Python, even though new to me, didn’t require compiling so prototyping applications promised to be quicker. Looking at the syntax, I concluded it is just like any other programming language, just has a different accent. I launched a demo program that reads a single channel. Damned if it didn’t work right out of the box! My short thermocouple test probe echoed the room temperature rather accurately, 20 degrees C (68 F to my wife’s dismay). I dipped the probe in an icy beverage, the display dropped to 0 degrees C, cool, er, COLD! On down to the basement where the thermocouples were routed during the chimney re- construction. Two flues, three thermocouples per flue, measuring temperatures at the bottom, middle, and top of the chimney, and two extra probes monitoring the burn temperature inside the woodstoves. 200 feet of wire all terminating in the furnace room. I carefully stripped the wires and inserted them into the screw-down terminals. I set up a small table to rest a computer monitor and keyboard so I can fiddle on the Pi right there. We’re all hams, so we know the importance of keeping the wiring and electronic devices secured properly to ensure proper operation. I ignore those rules: Since there was no AC outlet nearby to plug in the Raspberry Pi’s power wall wart, I ran an extension cord into the next room. Everything fired up nicely. Using the same demo program, I selected a channel to read the temperature. My heart sank when I received and error: “Common Mode Error”, WTF? Searching through the manufacturer’s web site, they describe the error meaning abnormally high voltages are present on the thermocouple wire exceeding the .8 VDC limit. “OH NO!” what does that mean? I tried another probe, same issue, “NUTS!” I pulled out a digital voltmeter and found I was getting around 50VDC on the thermocouple wires, where is this voltage coming from? The wires are not in contact with anything electrical, in fact, they are buried in the masonry of the chimney. I replaced the power supply, same issue. I’m dead. When the wires were installed, I didn’t have anything to verify each line was operating properly, just hoped things would work. This could be a total waste of time and money. With nothing else to lose, I unplugged the extension cord and tried another outlet. OMG, the error is gone and realistic temperatures are coming in! There must be a floating ground or something weird with the outlet I first was plugged into. I’ll worry about that later but not too much later – that could be a bad thing. The Python libraries included examples of strip chart and web server code. This could be fun! Some more fiddling around I ended up with something that is what I was hoping to accomplish: I am able to access the temperatures of both stoves and flues anywhere in the house, pc or phone via access the web server running on the Pi – slick as snot. In the chart above, the top red line represents the burn temperature inside the stove, the lines along the bottom reflect the flue temperatures, I’m sampling every 5 seconds. An interesting phenomena is observed, the lower probes in the flues show a slightly cooler temperature than the middle probes. The upper probes cool back off as the gasses exhaust outside. The flues are rather consistent through out the day. I monitor both stoves all day long and find this data very useful in notifying me when the stoves need re-feeding – very handy! So far, so good. I have other features I’d like to implement: logging, high temp alarms, monitor water heater and other fun stuff. Heating season is almost over, and chimney cleaning will be on the docket this summer, with camera. Goal? No more chimney fires and maybe play on the radio some more!
DELARANews

Craig

Craig Miller, W8CR

I have flu fever

Quick recap: Chimney fire almost burned the house down, replaced chimney, installed thermocouples in flues, plan to use Raspberry Pi to read thermocouples. Done. OK, the last we left this, Santa did deliver two Raspberry Pi “HATS” that allow one to connect up to 8 thermocouples. Way to go, Santa! Like a little boy on Christmas morning, I spent several hours figuring out how to install the hats and wire up the thermocouples. The hat manufacturer, Measurement Computing, supplied a nice set of libraries and sample code, online, to get me up and running in short order. I plugged in one board on the Pi. twisted together a short length of thermocouple wire and connected to one of the four terminals. They support two languages to talk to the hats, C++ and Python. It’s been years since I did any C and C++ programming and didn’t know anything about Python. Python, even though new to me, didn’t require compiling so prototyping applications promised to be quicker. Looking at the syntax, I concluded it is just like any other programming language, just has a different accent. I launched a demo program that reads a single channel. Damned if it didn’t work right out of the box! My short thermocouple test probe echoed the room temperature rather accurately, 20 degrees C (68 F to my wife’s dismay). I dipped the probe in an icy beverage, the display dropped to 0 degrees C, cool, er, COLD! On down to the basement where the thermocouples were routed during the chimney re- construction. Two flues, three thermocouples per flue, measuring temperatures at the bottom, middle, and top of the chimney, and two extra probes monitoring the burn temperature inside the woodstoves. 200 feet of wire all terminating in the furnace room. I carefully stripped the wires and inserted them into the screw-down terminals. I set up a small table to rest a computer monitor and keyboard so I can fiddle on the Pi right there. We’re all hams, so we know the importance of keeping the wiring and electronic devices secured properly to ensure proper operation. I ignore those rules: Since there was no AC outlet nearby to plug in the Raspberry Pi’s power wall wart, I ran an extension cord into the next room. Everything fired up nicely. Using the same demo program, I selected a channel to read the temperature. My heart sank when I received and error: “Common Mode Error”, WTF? Searching through the manufacturer’s web site, they describe the error meaning abnormally high voltages are present on the thermocouple wire exceeding the .8 VDC limit. “OH NO!” what does that mean? I tried another probe, same issue, “NUTS!” I pulled out a digital voltmeter and found I was getting around 50VDC on the thermocouple wires, where is this voltage coming from? The wires are not in contact with anything electrical, in fact, they are buried in the masonry of the chimney. I replaced the power supply, same issue. I’m dead. When the wires were installed, I didn’t have anything to verify each line was operating properly, just hoped things would work. This could be a total waste of time and money. With nothing else to lose, I unplugged the extension cord and tried another outlet. OMG, the error is gone and realistic temperatures are coming in! There must be a floating ground or something weird with the outlet I first was plugged into. I’ll worry about that later but not too much later – that could be a bad thing. The Python libraries included examples of strip chart and web server code. This could be fun! Some more fiddling around I ended up with something that is what I was hoping to accomplish: I am able to access the temperatures of both stoves and flues anywhere in the house, pc or phone via access the web server running on the Pi – slick as snot. In the chart above, the top red line represents the burn temperature inside the stove, the lines along the bottom reflect the flue temperatures, I’m sampling every 5 seconds. An interesting phenomena is observed, the lower probes in the flues show a slightly cooler temperature than the middle probes. The upper probes cool back off as the gasses exhaust outside. The flues are rather consistent through out the day. I monitor both stoves all day long and find this data very useful in notifying me when the stoves need re- feeding – very handy! So far, so good. I have other features I’d like to implement: logging, high temp alarms, monitor water heater and other fun stuff. Heating season is almost over, and chimney cleaning will be on the docket this summer, with camera. Goal? No more chimney fires and maybe play on the radio some more!