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| This should work right? |
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| paulca:
Si I'm attaching a Dallas One Wire DS18B20 to a Wemos Mini D1 and because I wanted to keep the effort to a minimum and make it easier to design the case for the pair I choose to use a GPIO pin as a ground. It allows me to connect the DS18B20 to 3.3V, D7 and D6 and poke out the side of the case. I then set D6 to OUTPUT and LOW to create a ground and D7 to INPUT_PULLUP to pull the dataline high. I connected it up and powered it and it is reading temperatures. However with a room temperature of around 21*C the temperature reads around 21*C when I power it on and slowly rises to 32*C after 5 minutes where it stabilises. This would suggest that either there is too much current flowing through the device, the device is damaged or it's just not going to work that close to the Wemos mini board and needs to be on leads. This probe has been through a few soldering and desoldering wars and I wouldn't exclude thermal damage. |
| Twoflower:
How warm does the controller board get and how long are the leads? It's possible that the increasing temperature comes from the controller board through the leads of the temp sensor. To test this you can place a fan blowing over the processor and Sensor. If the difference is now less than 11°C you know that there's some heat-source influencing the sensor. If the ESP is active especially with active WLAN it does consume some power and can heat up the PCB. |
| paulca:
--- Quote from: Twoflower on October 06, 2019, 02:30:49 pm ---How warm does the controller board get and how long are the leads? It's possible that the increasing temperature comes from the controller board through the leads of the temp sensor. To test this you can place a fan blowing over the processor and Sensor. If the difference is now less than 11°C you know that there's some heat-source influencing the sensor. If the ESP is active especially with active WLAN it does consume some power and can heat up the PCB. --- End quote --- Using the "upper lip" test the ESP8266 chip is luke warm to the touch. Spinning the device around in the air on the end of it's USB cable and I can get the temp to come down to ambient within about 30 seconds, but it slowly climbs again once stationary. I had no leads, just soldered the DS18B20 directly to the wemos mini. Aww well it was a nice idea, but if I need to put the probes on leads I'll just solder them normally to 3.3, GND and use an actual 4k7 pull up on the data line. Was hoping just having the tip of the TO-92 package sticking out the side of the case would work, but it is probably too close to the heat source of the ESP chip :( |
| paulca:
Well, a great idea, but a fail: |
| Twoflower:
Yes for temp sensors you have to consider the heat-flow through the leads as well. Especially since most metals are not only good electrical conductors (surprise) but also temperature conductors. In your case you should use thin wires and also keep in mind that the housing will get warm over time as well. So for good readings you might need to get creative to reduce the influence from the nearby heat-source (shilding, insulation, distance, ...). So before re-do the soldering over and over again, use longer leads and try different things to find a solution that works for you. And then do the final wiring with the thing you just learned in mind. Not sure if that'll do, I would change the case a bit: Try to place a double-wall between the sensor and the controller. 2-5mm in between. the wall to the controller could be thin as it only needs to prevent the warm air to enter the chamber. This will work as a double walled thermos flask. And optionally fill the area between the walls with a foam (as foam is a good thermal insulator). But the wires should be much longer to prevent the heat flowing through them. For example 5cm of magnet wire. As it is thin to reduce the heat running through them. Loop the wire in the 'chamber'. |
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