The colors are meant to follow the visible spectrum (remember ROY G BIV?). So eventually, everyone switched to bands. The dot, as with printed piece of text on the cylindrical, might be hidden from view depending on the position of the resistor. The code soon extended to capacitors (condensers, in the contemporary parlance). Here’s the color code chart from the 1941 Radio Today yearbook:Īds in that magazine promoting resistors were careful to note that they were RMA color-coded. Radios using this scheme started to appear in 1930. The “tip” of the resistor would be the 2nd band and a dot would be the multiplier. So the bulk of the resistor would be the first band color. In some cases, the third band was actually a dot. Then there would be two or three other bands to show the rest of the value. The standard for colors was the same, but the body of the resistor acted as the first band. The solution was color bands, but not quite as we know them today. The problem was that marking small components is difficult, especially back in the 1920s. This is the tale of how color bands made their way onto every through-hole resistor from every manufacturer in the world.ĭots Then Bands Ésistances anciennes annees 50 by François Collard, CC-BY-SA 4.0īy the late 1920s, the RMA was setting standards and one of them was the RMA standard for color-coding. It exploded into several specific divisions, but that’s another story. There would be several more name changes over the years until finally, it became the EIA or the Electronic Industries Alliance. Almost immediately the name changed from “Associated Radio Manufacturers” to the “Radio Manufacturer’s Association” or RMA. The idea was to share patents among the members. Then in 1924, 50 radio manufacturers in Chicago formed a trade group. But why are they marked like this? Like red stop signs and yellow lines down the middle of the road, it just seems like it has always been that way when, in fact, it hasn’t.īefore the 1920s, components were marked any old way the manufacturer felt like marking them.
Through-hole resistors have color codes, and that’s generally where beginners begin. One of the first things you learn in electronics is how to identify a resistor’s value.
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