Saturday, October 2, 2010

Making my thermostat

A few days ago, the shipment from futurlec with my electronic components finally arrived. It took them almost a full month to get shipped and arrive here. Inside the envelope there were a lot of separate plastic bags, all labeled with what was inside. That's convenient.

After a closer look on the multimeter, I saw a big crack in the plastic and the screen was completely loose inside the case. So obviously it didn't display anything. I've sent them an email about this, but they haven't replied yet. I hope I'll get my money back or get a new one. While waiting for their answer, I borrowed one from my grandpa so I could build my thermostat.

I've worked on this all morning, so I was hoping it would work. But it didn't. The voltage to set the desired temperature only goes up to 60mv. So the thermostat can only regulate temperatures up to 6°C. On the positive side: the led goes on for about 2 seconds before turning off, so I think the hysteresis is working, but it never gets cold enough again to make it go back on once it goes off.

I started measuring if all the resistors were correct and found that the potentiometer is 5k instead of the 2k I ordered. All the other ones were correct. I bought the 2k one because futurlec didn't sell 2.2k. I had already send them an email about the broken multimeter and didn't want to send an other one for something worth less than 1€ so I just ordered a 2.2k potentiometer from ebay. I hope everything will work with the correct potentiometer installed. Below I've added a picture of my thermostat. The broken corner is my fault, I dropped the board while I was unpacking it. Luckily its only a small corner that went away, and the rest is intact.

And while I'm talking about electronics, I might as well mention that I'm still waiting for everything from mendel-parts to be shipped. The electronics have arrived in their shop, but my order hasn't been shipped yet. I suppose sending 50 order in one day is a little too much for them. I couldn't do that either.I hope everything will arrive before next weekend, so I can finally start building my Mendel.

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