RPi Tutorial EGHS:LED output - Revision history

Meltwater: /* Circuit 2 - LED Driving Circuit (using Transistor Switching Circuit) */

2012-12-08T09:06:55Z

‎Circuit 2 - LED Driving Circuit (using Transistor Switching Circuit)

Meltwater: /* Circuit 2 - LED Driving Circuit (using Transistor Switching Circuit) */

2012-12-08T09:06:30Z

‎Circuit 2 - LED Driving Circuit (using Transistor Switching Circuit)

Meltwater: /* Basic LEDx8 Test Module */

2012-03-21T10:10:41Z

‎Basic LEDx8 Test Module

Meltwater: /* Circuit 2 - LED Driving Circuit (using Transistor Switching Circuit) */ - removed in-progress notes (so please correct anything you see is wrong)

2012-03-13T08:57:55Z

‎Circuit 2 - LED Driving Circuit (using Transistor Switching Circuit): - removed in-progress notes (so please correct anything you see is wrong)

Bredman: Warning that an NPN transistor is needed

2012-02-24T21:51:27Z

Warning that an NPN transistor is needed

Meltwater: /* Circuit 2 - LED Driving Circuit (using Transistor Switching Circuit) */

2012-02-22T12:36:37Z

‎Circuit 2 - LED Driving Circuit (using Transistor Switching Circuit)

Meltwater: /* Circuit 2 - LED Driving Circuit (using Transistor Switching Circuit) */

2012-02-22T12:35:48Z

‎Circuit 2 - LED Driving Circuit (using Transistor Switching Circuit)

Meltwater: /* Circuit 2 - LED Driving Circuit (using Transistor Switching Circuit) */

2012-02-22T12:34:06Z

‎Circuit 2 - LED Driving Circuit (using Transistor Switching Circuit)

Meltwater: /* Theory */

2012-02-22T12:33:28Z

‎Theory

Meltwater: /* Circuit 2 - LED Driving Circuit (using Transistor Switching Circuit) */

2012-02-22T12:32:37Z

‎Circuit 2 - LED Driving Circuit (using Transistor Switching Circuit)

← Older revision		Revision as of 09:06, 8 December 2012
Line 80:		Line 80:
	In order to drive a slightly higher current, the use of a transistor circuit will be required. Since all the driving current will be drawn through Vcc and through the transistor, the RPi 5volt line can be used for Vcc (this will limit the available current to 1Amp total draw from the USB supply itself - including the RPi draw). The current limit will be the nominal current the transistor can handle.		In order to drive a slightly higher current, the use of a transistor circuit will be required. Since all the driving current will be drawn through Vcc and through the transistor, the RPi 5volt line can be used for Vcc (this will limit the available current to 1Amp total draw from the USB supply itself - including the RPi draw). The current limit will be the nominal current the transistor can handle.

−	Note: Vcc = 5V in this example, but the 3V3 supply can be used too, although remember that the 3V3 should be not used to supply over 120mA.	+	Note: Vcc = 5V in this example, but the 3V3 supply can be used too,
		+	although remember that the 3V3 should be not used to supply over
		+	120mA in total.

← Older revision		Revision as of 09:06, 8 December 2012
Line 79:		Line 79:

	In order to drive a slightly higher current, the use of a transistor circuit will be required. Since all the driving current will be drawn through Vcc and through the transistor, the RPi 5volt line can be used for Vcc (this will limit the available current to 1Amp total draw from the USB supply itself - including the RPi draw). The current limit will be the nominal current the transistor can handle.		In order to drive a slightly higher current, the use of a transistor circuit will be required. Since all the driving current will be drawn through Vcc and through the transistor, the RPi 5volt line can be used for Vcc (this will limit the available current to 1Amp total draw from the USB supply itself - including the RPi draw). The current limit will be the nominal current the transistor can handle.
		+
		+	Note: Vcc = 5V in this example, but the 3V3 supply can be used too, although remember that the 3V3 should be not used to supply over 120mA.

@@ Line 63: / Line 63: @@
 ====Basic LEDx8 Test Module====
 Basic LEDx8 Test Module (Control pins at top, GND connection at bottom-right).
-[[File:EGHS-LEDx8TestModule.jpg|100px|thumb|left|Basic LEDx8 Test Module]][[File:EGHS-LEDx8TestModuleDetailed.jpg|100px|thumb|centre|Circuit with track breaks marked in red]]
+[[File:EGHS-LEDx8TestModule.jpg|200px|thumb|left|Basic LEDx8 Test Module]][[File:EGHS-LEDx8TestModuleDetailed.jpg|200px|thumb|centre|Circuit with track breaks marked in red]]
@@ Line 70: / Line 72: @@
 The above test module has been built to allow easy testing of GPIO outputs by driving up to 8 LEDs.
 The resistor value 330 ohms is used (keeps the current draw fairly low).
 ===Circuit 2 - LED Driving Circuit (using Transistor Switching Circuit) ===

@@ Line 74: / Line 74: @@
 ===Circuit 2 - LED Driving Circuit (using Transistor Switching Circuit) ===
 [[File:EGHS-LEDhigh output2.jpg|250px|thumb|left|Higher Power LED Driving Circuit]]
 ''For more detailed information about basic transistor circuits, some useful information is here<ref>[http://www.kpsec.freeuk.com/trancirc.htm The Electronics Club:Transistor Circuits].</ref>''
@@ Line 115: / Line 110: @@
 Transistors do have a limited amount of current handling ability, which can be improved by coupling together as a [http://www.kpsec.freeuk.com/components/tran.htm#darlington Darlington pair] (often available in a single package).  Also higher powered switches such as mosfets, and even relays can be driven for higher power requirements.
 ====Calculating R1 - LED Current Limiting Resistor====
@@ Line 136: / Line 128: @@
 ====Calculating R2 - Transistor Base Resistor====
 The value of R2 can be determined, as follows:
- --- NOTE ---
- Calculations may be wrong, still researching at the moment...
- --- NOTE ---
 There seems to be two possible ways to approach this, one is to work out your required driving current through the collector (Ic) i.e. the driving current of the LED, and the other is to determine it's value from the recommended source current of the GPIO pin (for the RPi, 5mA or less is recommended).

← Older revision		Revision as of 21:51, 24 February 2012
Line 86:		Line 86:

	====Transistor Selection====		====Transistor Selection====
		+	This circuit requires an NPN transistor. This circuit is not suitable for other types of transistor (example PNP, FET).
		+
	There is a huge range of transistors available, so I will pick a common & cheap one ([http://uk.farnell.com/fairchild-semiconductor/bc548/transistor-npn-to-92/dp/1467872 BC548] or [http://uk.farnell.com/multicomp/bc108/transistor-npn-to-18/dp/9206736 BC108]) and see how well it suits.		There is a huge range of transistors available, so I will pick a common & cheap one ([http://uk.farnell.com/fairchild-semiconductor/bc548/transistor-npn-to-92/dp/1467872 BC548] or [http://uk.farnell.com/multicomp/bc108/transistor-npn-to-18/dp/9206736 BC108]) and see how well it suits.

← Older revision		Revision as of 12:36, 22 February 2012
Line 80:		Line 80:


−	''For more detailed information about basic transistor circuits, some useful information is here<ref>[http://www.kpsec.freeuk.com/trancirc.htm (The Electronics Club:Transistor Circuits].</ref>''	+	''For more detailed information about basic transistor circuits, some useful information is here<ref>[http://www.kpsec.freeuk.com/trancirc.htm The Electronics Club:Transistor Circuits].</ref>''

	In order to drive a slightly higher current, the use of a transistor circuit will be required. Since all the driving current will be drawn through Vcc and through the transistor, the RPi 5volt line can be used for Vcc (this will limit the available current to 1Amp total draw from the USB supply itself - including the RPi draw). The current limit will be the nominal current the transistor can handle.		In order to drive a slightly higher current, the use of a transistor circuit will be required. Since all the driving current will be drawn through Vcc and through the transistor, the RPi 5volt line can be used for Vcc (this will limit the available current to 1Amp total draw from the USB supply itself - including the RPi draw). The current limit will be the nominal current the transistor can handle.

@@ Line 80: / Line 80: @@
-''For more detailed information about basic transistor circuits, some useful information is here<ref>[http://www.kpsec.freeuk.com/trancirc.html(The Electronics Club:Transistor Circuits)].</ref>''
+''For more detailed information about basic transistor circuits, some useful information is here<ref>[http://www.kpsec.freeuk.com/trancirc.htm (The Electronics Club:Transistor Circuits].</ref>''
 In order to drive a slightly higher current, the use of a transistor circuit will be required.  Since all the driving current will be drawn through Vcc and through the transistor, the RPi 5volt line can be used for Vcc (this will limit the available current to 1Amp total draw from the USB supply itself - including the RPi draw).  The current limit will be the nominal current the transistor can handle.
@@ Line 88: / Line 88: @@
 There is a huge range of transistors available, so I will pick a common & cheap one ([http://uk.farnell.com/fairchild-semiconductor/bc548/transistor-npn-to-92/dp/1467872 BC548] or [http://uk.farnell.com/multicomp/bc108/transistor-npn-to-18/dp/9206736 BC108]) and see how well it suits.
-''More details on specific transistors see <ref>[http://www.kpsec.freeuk.com/components/tran.html (The Electronics Club:Transistor)]</ref>''
+''More details on specific transistors see <ref>[http://www.kpsec.freeuk.com/components/tran.htm The Electronics Club:Transistor]</ref>''
 The key characteristics of interest are:

← Older revision		Revision as of 12:34, 22 February 2012
Line 80:		Line 80:


−	''For more detailed information about basic transistor circuits, some useful information is here<ref>[http://www.kpsec.freeuk.com/trancirc.~~htm here~~ (The Electronics Club:Transistor Circuits)].</ref>''	+	''For more detailed information about basic transistor circuits, some useful information is here<ref>[http://www.kpsec.freeuk.com/trancirc.html(The Electronics Club:Transistor Circuits)].</ref>''

	In order to drive a slightly higher current, the use of a transistor circuit will be required. Since all the driving current will be drawn through Vcc and through the transistor, the RPi 5volt line can be used for Vcc (this will limit the available current to 1Amp total draw from the USB supply itself - including the RPi draw). The current limit will be the nominal current the transistor can handle.		In order to drive a slightly higher current, the use of a transistor circuit will be required. Since all the driving current will be drawn through Vcc and through the transistor, the RPi 5volt line can be used for Vcc (this will limit the available current to 1Amp total draw from the USB supply itself - including the RPi draw). The current limit will be the nominal current the transistor can handle.

@@ Line 30: / Line 30: @@
        be between the RPi 3.3V pin and the GPIO pin (rather than GPIO pin and GND).
-''For additional detail see <ref>[[http://www.scriptoriumdesigns.com/embedded/gpio_out.php Introduction To Embedded Programming - GPIO Output]]</ref>''
+''For additional detail theory see'' <ref>[http://www.scriptoriumdesigns.com/embedded/gpio_out.php Introduction To Embedded Programming - GPIO Output]</ref>
 ===Circuit 1 - Basic LED Driving Circuit===