Embedded Systems/Low-Voltage Circuits

Low voltage circuits, in this field of consideration can essentially be considered circuits that never exceed the pin voltage (or exceed it by small amounts). If the voltage never goes any higher, and if we keep our current under control, we risk very minimal damage to our embedded systems.

Example: Lighting LEDs

As a very simple example we would like to light a series of LED (Light-Emitting Diodes) from an output pin on an embedded computer. Consider that our output pin can source 15mA at +5V. However, we also need to consider that our LED requires at least 10mA to light, and our LED can not exceed +5V. If the voltage on the LED get's too high, the LED could pop (it's an actual pop, cover your eyes).

Using ohm's law on the pin, we can find the minimum resistance for the circuit:

$+5V=(20mA)r_{min}\to r=250\mathrm{\Omega }$

Now, if we use Ohm's law on the diode, we can figure out the maximum resistance (the resistance that makes the LED not light up).

$+5V=(10mA)r_{max}\to r=500\mathrm{\Omega }$

So we know that our resistance, r, needs to be between 250 and 500 Ohms.

further reading

• Analog and Digital Conversion