CPC Issue 110 - Temperature Sensor Correction

[Gareth Halfacree]

Reader John Knight has written in with a criticism of my Arduino-powered temperature-sensitive LED controller on page 110 of - oddly enough - issue 110, stating that my calculation for working out the value of current-limiting resistor required for a given LED in step 3 is absolute gibberish.

Do you know what? He's completely right.

When writing the article, I apparently had a brainfart and wrote the equation as R=(Vs x Vf)/I rather than R=(Vs-Vf)/I. That wouldn't have been *too* bad, if when writing the instructions to go with said equation I hadn't based them on the typo'd version.

Mea maxima culpa.

If you're curious, this is how step 3 *would* have read had I not apparently been asleep on the job:
If you’re using the recommended RGB LEDs from open-source hardware specialist www.oomlout.co.uk, you can skip this step, as the correct resistors are provided. If not, use the formula R=(Vs-Vf)/I, where the resistance, R, is calculated by subtracting the LED’s forward voltage drop from the source voltage – 5V – and dividing the result by the LED’s rated current in amps. For most RGB LEDs, this works out at 270 Ohms.

There'll be a correction printed in next month's CPC, Ben tells me. In the meantime, accept my humble apologies, dear readers.

[NethLyn]

Fast correction; the benefit of subscribers

I'll just hijack this thread to say that the PSU Labs is as good as always, as one of the two guaranteed issues I buy off the shelf each time there's a labs. If the GPU labs is definitely in next month's, that'll be the other one.

[Kovoet]

Must be a northern thing lol. Thanks for letting us know in advance