Direct Thermocouple Measurement with the ARD-LTC2499
One of the unique uses of the ARD-LTC2499 24-bit Analog to Digital Convert Shield is to measure thermocouples directly. Conventional solutions for digitizing thermocouples use a MAX31855 or MCP9600 to convert the voltage to a usable temperature, but these solutions need one part for each thermocouple sensor, and the part is tied specifically to the type of thermocouple being used. By using the LTC2499 to measure the thermoelectric voltage directly, we can measure up to 8 thermocouples per board, and because all of the conversion is done with math on the host processor, you can have any mix of thermocouple types that you want. It’s remarkably easy to do, and I’ll show you how just how easy it is to get started.
Thank you to everyone who joined the ProtoThrottle Q&A today. For those who missed it, or would like to go back and review the presentation, you can view the recording on YouTube:
The slides from the presentation are available here.
The demonstration videos can also be found on YouTube:
Your Old Power Pack Isn’t a DC Supply
Please don’t power electronics from your old “DC” power pack.
It’s a rare day when I see a layout that doesn’t have a cheap train set power pack powering some accessory somewhere in a corner. It makes me shudder every time I see it, because if it’s powering any electronics, that’s just asking for trouble. I understand it – most model railroaders aren’t electronics people, and we’re all a little cheap and like to get every possible decade of use out of something that we can. But it’s a bad, bad idea, and I’m here today to explain why.
The problem is that these old packs were designed to do one thing – apply track power and spin a motor – and weren’t even terribly good at that. The “DC” that they put out can only barely be called that. It’s full-wave rectified AC from the transformer that’s probably going through a primitive rheostat and sent straight to the output. There’s no filtering and no regulation at all. At low load (such as a modern piece of electronics), this means you get DC that cycles between near 0 volts and around 26-30 volts at 120 times per second, even with the “throttle” barely turned on. Often the electronics blow up from being pushed beyond their ratings, the customer doesn’t understand why, the manufacturer and product get blamed, and nobody’s happy. So I’m here today to explain it and tell you: throw that power pack away!