https://hackaday.io/project/188104-the-great-resistorThis idea was born when I saw this project years ago: https://hackaday.io/project/170961-resistor-color-code-clock-v10
The best choice seemed to be a Arduino Nano clone, who can handle a 16 Bit ADC, NeoPixels and one OLED. The range of mensurable resistors values lies between 0 Ohm - 15 M Ohm. The sweet spot is 33k Ohm. A voltage divider with one known resistor is the main module of this device. To acquire the divided voltage I used a ADS1115 16-Bit ADC. The supply voltage should be 5 volts, but while the WS2812 addressable RGB LED are using the same 5V source, the 5V rail is also been measured, since the supply voltage drops quite a bit. With the ratio of those two voltages and the one know resistor it is easy to find out the unknown resistor.
The measurement is still a bit noisy. To tackle that I wanted to use a rollingAverage library, but it could not handle uint16_t. I will have to write my own little average function. The very high (>2 M Ohm) an low (<100 Ohm) values are a bit off. I might try to find a solution for that, or I'll just life with it. I might look into the way how a multimeter is doing it. I would be easy to operate this device with a LiPo, but I am not sure how the noise of the setp-up module would affect the measurement.
Measuring a resistor and translate the number to a color sounds easy, but I had to find out the first three digits of the acquired unknown resistor for further processing. To get only one of the first three digits I pushed the result into an array and checked the first, second and third array field. Corresponding to the resulting number will be assigned to the equivalent color.
The build of the glowing resistor contains 15 RGB LEDs also it includes light blocking black foam, so the single bands can be shown with high contrast. The 'arms' of the resistor are made out of hot glue sticks covered with aluminium tape. Another two RGB LEDs are shining into another hot glue stick supporting the base in the front. The base is a half of a real breadboard.
This is how the resistor value is getting calculated (except step IV):
(My old project "EC-Meter": https://hackaday.io/project/171107-ec-meter-hdr-16-bit-adc)
At last I added one OLED 128x64 OLED display (SSD1306) to show the measured resistor value.
A 100k NTC resistor will make this build to one well over engineered thermometer!
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