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Thermochromic breadboard

Why

When working on a solderless breadboard (not only there, but... well...), it often happens that a power rating of some part is exceeded or its cooling is insufficient. It would be beneficial to see such situations before the parts express their distress with a smoke signal.

How

A breadborad was modified with a thermochromic paint, mixed from a white acrylic model-grade paint and a thermochromic pigment obtained from Middlesex University Teaching Resources webshop, using a makeshift pot made from the bottom part of a beverage can. The orange color was chosen on the basis of availability (read: mistakenly ordering four oranges instead of intended four different hues.) The threshold temperature of the pigment was chosen also on the basis of availability (they did not have any other than 29-30 °C).

The active area, where the parts are located by at least one pin, was coated with the mixed paint. Care was taken to not let too much of it drip into the pin holes. The power buses were not painted.


Original breadboard

Adding pigment

Mixing the paint

Painted breadboard

Results

The first tests were done during a particularly warm summer night, when the indoor temperature reached close to threshold temperature of the pigment. At such conditions, the sensitivity of the paint was outstanding; a 250-milliwatt resistor loaded with 350 milliwatts shown a color change around its leg within several seconds.

The reverse change was much slower. Due to some hysteresis of the pigment and the closeness of the room temperature to the threshold temperature, the thermal trace was present for a fairly long time (minutes). Putting the board out of the window, where the temperature was slightly lower, markedly accelerated restoring of the color.

The thermal trace (the discoloration of the pigment) tended to bleed around the board as its material spread the heat. The width of the trace, and the speed of its spreading, can provide a visual clue about how much is the part heating.

Caveat: The color change shows the part's color indirectly. There is a delay between the temperature change of the part itself and temperature change of the board, which is usually provided via thermal conduction through the part's legs. There is also a thermal differential between the part itself, along its leg, and over the board.


Resistor heated with current

Resistor heated with current

Resistor heated with current

Breadboard showing residual thermal image

Possible improvements


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