10 CodeBug Projects in 10 Days: Flashing an LED

RE: 10 CodeBug Projects in 10 Days: Flashing an LED

volly — Wed, 27 Jul 2016 12:43:11 GMT

Yep....haven't we all learn't a lot from the Raspberry pi and BeagleBoneBlack LED/resistor, infinite number of projects and what-if....scenarios.....

Still cool to revisit and echo here....

RE: 10 CodeBug Projects in 10 Days: Flashing an LED

Former Member — Wed, 11 Nov 2015 20:26:23 GMT

Cool projects....

RE: 10 CodeBug Projects in 10 Days: Flashing an LED

jc2048 — Fri, 02 Oct 2015 10:23:21 GMT

It might be worth pointing out that in the real world diodes aren't perfect and require a certain amount of voltage to be present before they start to conduct. That's called the forward voltage (Vf on a datasheet). The manufacturer will specify it for a particular current (because it changes as the current changes). For the kind of small-signal silicon diodes used in circuit design (like the 1N914), that don't emit light, that voltage is something like 0.6V [specified at a few mA]. For LEDs, which are made with semiconductor materials other than silicon, the forward voltage is quite a bit higher. Red LEDs usually have a forward voltage around 2V and will work ok in your circuit whether powered by the USB's 5V or the 3V of a button cell [I haven't seen a schematic of the board and don't know how they are handling the power, but I presume you either see 5V or 3V depending on the source, or they might be regulating the +5V from the usb down to 3V so you always see 3V irrespective of which source it's coming from]. What I'm coming to [excuse the meandering path I'm taking] is that high-brightness white, green and blue leds often have forward voltages that are more like 3V or a little higher, so you may find that your LED will illuminate on +5V from the USB but not on the 3V (or less) from a button cell.

RE: 10 CodeBug Projects in 10 Days: Flashing an LED

mcb1 — Thu, 01 Oct 2015 20:58:49 GMT

Dave

Out of curiosity what limits the current the pin can supply.

I would have thought a resistor in series is good practice ... mainly because not all micors have inbuilt limiting (either by battery or the chip).

Mark