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voltage in the range 6-20V (although 7-12V is recommended).
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Wiring up multiple LEDs in series to a single arduino pin
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Wiring up multiple LEDs in series to a single Arduino pin
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=========================================================
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First, lets think about a single LED.
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The arduino pin, when raised high, is at 5V and no more than 20mA can
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The Arduino pin, when raised high, is at 5V and no more than 20mA can
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be taken from it. The LED will take about 10mA and wants about 1.5V.
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You can think of this as a potentiometer arrangement, with the
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You can see that beyond three or perhaps, at a push, four LEDs you're
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not going to get the required 1.5V across each LED. So three (or four)
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is the limit to how many LEDs you can drive in series from one pin on
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Wiring up multiple LEDs in parallel to a single arduino pin
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===================================--======================
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Wiring up multiple LEDs in parallel to a single Arduino pin
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===========================================================
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Imagine we have this
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| '---|___|----►|---+--- GND
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This is ok. R1 and R2 are just the usual 340 ohms. But we have to
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This is OK. R1 and R2 are just the usual 340 ohms. But we have to
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bare in mind that each LED requires 10mA. So the total current drawn
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from the arduino pin will be 20mA, which is the most you're allowed to
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from the Arduino pin will be 20mA, which is the most you're allowed to
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draw. So two LEDs is the most that we can drive, in parallel, directly
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Using a transistor to drive multiple LEDs
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=========================================
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In both of the following diagrams, the resistor on the arduino pin,
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In both of the following diagrams, the resistor on the Arduino pin,
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R1, just needs to be something suitably high to provide a small
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current on the base of the transistor. So, R1 could be 1kΩ.
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| +-------+-------'
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Arduino | ___ ,-|
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Here, R3 = R4 = R5 = 340Ω, as usual. The numbher of LEDs is limited
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Here, R3 = R4 = R5 = 340Ω, as usual. The number of LEDs is limited
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only by the current that can be drawn from the power supply.
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An RC (resistor capacitor) curcuit is a basic low-pass filter. Here
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An RC (resistor capacitor) circuit is a basic low-pass filter. Here
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we're talking about giving it a pulse wave signal (a voltage that
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oscillates between 0V and approx. 5V).
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When using an NPN transistor as a switch, a typical set up might look
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o--------------+---- 5V
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o---[___]--b(|↘ ) T (NPN)
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You would typically connect the pin to 5V to turn on the transistor.
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The current between the emitter and base turns on a larger current
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between the emitter and collector. The resistor, R, limits the
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turn-on current and prevents a short (effectively) across the
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transistor (and whatever the pin is connected to, such as an
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PNP transistors were used in the days when a -5V rail was typical
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instead of a 5V rail. In this case, a typical set up would be exactly
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the same as above, but with -5V used for the top rail and a PNP
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transistor. The thing to note here is that the direction of the
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current would also have changed. Now imagine flipping this diagram
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up-side-down and offsetting both rails by +5V (so that -5V becomes GND
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and GND becomes 5V, respectively). Then you'd have this set up, which
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is a modern-day typical usage scenario for a PNP transistor.
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o---[___]--b(|↙ ) T (PNP)
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o--------------+---- GND
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In this set up, as before, a current is required between the base and
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emitter to turn on a larger current between the collector and emitter.
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But the difference this time is that the pin must be connected to
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ground to achieve this.
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Two capacitors in parallel are equivalent to one capacitor whose
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value is the sum of the two.
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COMMON PARTS LIST AND USEFUL VALUES
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===================================
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BC548/BC547, 5V switch
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BC327/BC328, -5V switch
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With 5V across them, a 560Ω resistor is required.
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Electrolytic Capacitor (Radial, 4700uF 16V)
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Maplin part no. VH57M
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Arduino-powerable relay (DPDT, gold contacts, 5V, 27mA)
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Maplin part no. N05AW
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