3 ms·
Those solderless breadboards seem to be too much trouble. I still like the perf boards with the little copper rings for each hole. This is a very good form fa
by fuzzfactor 4y ago
Those solderless breadboards seem to be too much trouble.
I still like the perf boards with the little copper rings for each hole.
This is a very good form factor. There are supposed to be enclosures having a perfect fit to these boards.
In the video, the first IC he shows a spec sheet for is a MCP9700, an analog linear temperature sensor. He doesn't use it in a circuit here.
But it's not a very complex IC, plus has the thermistor within the package, and only needs 3 connection points, so the traditional through-hole TO-92 package version looks just like a simple 3-legged silicon transistor. Not smaller than a grain of rice like the SOT version.
You power it with a steady DC supply of about 3.5 to 5V on the + and ground leads, and it basically outputs the temperature as a steady analog voltage on the third lead. As the temperature of the component changes, the analog output voltage changes accordingly. For the MCP9700, over the range of 0.1V to 1.75V output, at temperatures from -40 to +125 Celsius.
There are nice handy digital displays that contain their own analog-to-digital converter, and if you hooked up the analog output lead from the little IC, to the input of the display, you would see those 0.1 to 1.75 volts digitally on the display. To make the display show the temperature in desired units like Fahrenheit or Celsius, ideally you would need to adjust the "span" of the display while subjecting the sensor to known reference temperatures such as a low of 0C (ice point of pure water), to a high of 100C (boiling point of pure water at sea level). This span adjustment not only changes the slope of the linear function being displayed, but also calibrates that particular sensor/display assembly at that particular DC supply voltage against two physical references which could be revalidated in the future if desired.
Different components or different batches are only within a few degrees of each other, according to the spec, but calibration of any one component similar to the above technique can correct for that.
As a finishing touch once the slope is set as realistically as possible against the high & low reference temperatures (or alternatively reference voltages), a final "zero" adjustment is made which now changes the intercept of the linear function being displayed while leaving the slope the same. IOW use a third reference temperature somewhere in the middle between your low & high 0C & 100C, and finally adjust the "zero" control for the display to match this "mid-point" reference thermometer. For instance if you were going to use one of these sensors to display room temperature most of the time, after setting the span, it would be good to check it against a known good thermometer at a temperature about 25C, then finely adjust the display to match the reference using the "zero" control.
If the particular display doesn't have adequate zero & span controls, you may need to come up with the proper peripheral components like variable resistors to make the adjustments. You may need to set your own decimal point too.
OTOH you could always go all the way and make your own A/D circuit with nixie tubes for display :)
They used to have sensors like this at Radio Shack and I used one to make a research temperature controller good to within 0.001F. No display, the TO-92 sensor was submerged in silicone oil in the bottom of a narrow glass tube mimicing a thermometer, had 3 wires leading out of the heated zone into a little box containing a high-gain fixed-slope comparator, and one external knob for "zero control". A separate certified thermometer in the same heated zone had to be there anyway.
Also, notice at 11:15 the way he carefully handles the lead-free solder, making sure it's all in its proper place so that problems will be greatly minimized.