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An IR Led emitter combined with an IR receiver can make an opto-isolator.
By using an opto isolator we can transfer information between circuits without an electrical connection.
In opto isolators the emitter is always an IR LED.
The receiver can be a photo-diode or a photo-transistor.
Photo transistors are transistors using the base as "light" sensor. When light strikes the photo transistor's base, it will conduct otherwise it will insulate.
Photo-diodes, on the other hand, are semiconductors that produce current flow when they absorb light.
There are two types of photo-diodes theĀ photovoltaics and the photoconductors.
The photovoltaics when they absorb light create a voltage difference between the edges.
Photoconductors areĀ reverse biased photo diodes. When they absorb light the reverse biased resistance will decrease.
Notice that a photo-transistor is nothing else than a reverse biased photo-diode + a normal transistor.

Photodiode and photo transistor
Photo diode and photo transistor


...continue reading "Infrared emitters & receivers"

Relay 5V

In this article we will talk about relays.
The relay is a device that permits with a small voltage to pilot a reed switch.
How this device should be applied on the circuit ?
How can we place it on an arduino ?
All these answers will be cleared in a while.
Let's start with some theory to see what happens in detail.
At the top of the relay we can see the 5V as input pilot voltage.
And we can see the 10A limitation at the 250VAC of the reed switch.
So with a 5 Voltage we can "switch" a 250VAC device that can consume up to 10A (P=V*I=2,5KW).
If you need to pilot a device that consumes more you should use a "bigger" relay that fit at your needs.

...continue reading "Relay and arduino"