Transistor is suitable to use when switching within the same circuit. While if the power your switching is in completely different circuit then you would want to use a\u00a0optocoupler which is another kind of electric switch where only light\u00a0signal is sent between the two circuits keeping them isolated. (See our guide about Optocouplers<\/a>)<\/p>\n There are NPN and PNP transistors. The NPN ones switch on the low side (-) while PNP transistors switch on the high side (+). This is important difference and for example this difference would mean that the NPN transistor that we will be using in this example would not have been suitable for the RGB LED example <\/a>since there we would need to switch on the high side (+) as the RGB LED had 3 anodes (+) and only one cathode (-). In the RGB LED example the LED was not shining very bright at all since we could not provide a lot of power from the GPIO pin, a transistor solves such issues.<\/p>\n Disclaimer:<\/strong> If you don’t know resistor color codings to find correct resistors then you can click the link bellow<\/strong><\/p>\n First we just draw up the circuit without knowing the values of the resistors.<\/p>\n Here is what we know:<\/strong><\/p>\n Now we calculate the rest:<\/strong><\/p>\n Now that we have the voltage and current then R2 = 2,6 V \/ 0,00018 A = 14,4 k\u03a9\u00a0<\/em><\/strong><\/span> (We will use 15 k\u03a9 resistor for R2)<\/em><\/span><\/span><\/span><\/span><\/span><\/p>\n We we update our circuit wit\u00a0the calculated values of R1 and R2:<\/strong><\/p>\n Now we are ready to put this onto the breadboard:<\/strong><\/p>\n We will use GPIO 5 for the GPIO pin.<\/p>\n For the led then you can see in\u00a0the picture bellow then that you have two ways to identify the + and – or anode vs cathode. Its the length of the pins where the longer wire is the anode and the shorter is the cathode. If wires have been trimmed then you can usually also see it on the LED it self the flat side on the edge is the cathode or – as is shown on the picture to right here.<\/p>\n When looking up the spec for your transistor then the spec will usually show how the pin layout is so you can know which was it should turn.<\/p>\n For mine it was like this:<\/p>\n When putting the parts on the breadboard you should try to go by the circuit drawing instead of blindly following the breadboard drawing since its easier to make mistakes if not understanding the wiring.<\/p>\n If you are not familiar with breadboards and placement of the cobbler then check this link out.<\/a><\/p>\n We just had one button on a window with the caption “Toggle LED”.<\/p>\n In the window I added the following property:<\/p>\n The Window Open event was as follows:<\/strong><\/p>\n The open event of the window:<\/p>\n The button\u00a0box event:<\/strong><\/p>\n Now I was not 100% happy when running it, the LED was on when I booted the computer which is caused by the GPIO pin having undetermined state.<\/p>\n Everything else worked, the code was able to turn it on and off, and the LED was shining bright as it was not having to be conservative on the current it takes.<\/p>\n There was easy fix to that, adding 1k\u03a9 resistor between the GPIO pin and the ground.<\/p>\n Making the circuit like this:<\/p>\n After adding the 1k\u03a9 resistor then the LED was shut when batting the computer and it only got turned on and off when sending the signal from the program.<\/p>\n Thats is for now.<\/p>\n In this example we are going to let the GPIO pin control a transistor so that we can draw more power when controlling a LED than what the GPIO pin can supply. We will be using a simple LED in this example where we aim to draw 16 mA power (I could easily go higher … Continue reading Putting the GPIO pin behind transistor to get more current<\/span>
\nWe do not take any responsibility for possible errors in the guide or errors that you might do wiring it up. Incorrect wiring can result in damaged sensor or damaged Raspberry PI.<\/p>\nPieces we use are:<\/strong><\/h5>\n
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Drawing up the circuit:<\/strong><\/h5>\n
![\"TransistorsWithoutValues\"](\"https:\/\/i1.wp.com\/einhugur.com\/blog\/wp-content\/uploads\/2015\/10\/TransistorsWithoutValues.png?resize=317%2C385&ssl=1\")
<\/a><\/p>\n\n
\n
\n<\/em> (5V – 2,2V) \/ 0,016 A = 175\u00a0\u03a9\u00a0<\/em>\u00a0<\/span> (We will use 180\u00a0\u03a9)<\/em>
\n5 – 2,2 is because the LED will use 2,2 so we have to let the resistor take the rest of the 5 V which means resistor will be at 2,8 V.<\/span><\/li>\n\n
\nWhich means I(B) will be: 0,016 \/ 90 = 0,00018 A<\/span>\u00a0(This is how little we will be taking from the GPIO pin)\u00a0<\/span><\/span><\/span><\/li>\n<\/ol>\n<\/li>\n<\/ul>\n![\"Transistor](\"https:\/\/i2.wp.com\/einhugur.com\/blog\/wp-content\/uploads\/2015\/10\/Transistor-Experiment.png?resize=320%2C390&ssl=1\")
<\/a><\/p>\n![\"LED](\"https:\/\/i0.wp.com\/einhugur.com\/blog\/wp-content\/uploads\/2015\/10\/LED-Explained.png?resize=278%2C168&ssl=1\")
<\/a><\/p>\n![\"2N3904\"](\"https:\/\/i1.wp.com\/einhugur.com\/blog\/wp-content\/uploads\/2015\/10\/2N3904.png?resize=200%2C145&ssl=1\")
<\/a><\/p>\n![\"TransistorExperimentbb\"](\"https:\/\/i0.wp.com\/einhugur.com\/blog\/wp-content\/uploads\/2015\/10\/TransistorExperimentbb.png?resize=474%2C335&ssl=1\")
<\/a><\/p>\n![\"GPIO](\"https:\/\/i1.wp.com\/einhugur.com\/blog\/wp-content\/uploads\/2015\/09\/GPIO-Header-152x300.png?resize=152%2C300&ssl=1\")
<\/a><\/h1>\nThe Xojo code for this one\u00a0really simple as this was more of electric guide than coding guide<\/strong><\/h1>\n
Protected ledOn As Boolean = false<\/pre>\n
Sub Open()\n GPIO.SetupGPIO\n GPIO.PinMode(5,GPIO.OUTPUT)\n GPIO.DigitalWrite(5,GPIO.OFF)\nEnd Sub<\/pre>\n
Sub Action()\nif ledOn then \nGPIO.DigitalWrite(5,GPIO.OFF)\nledOn = false\nelse \nGPIO.DigitalWrite(5,GPIO.ON)\nledOn = true\nend if\nEnd Sub\n\n<\/pre>\n
Un determined state on the GPIO pin at startup<\/h4>\n
![\"Transistor](\"https:\/\/i2.wp.com\/einhugur.com\/blog\/wp-content\/uploads\/2015\/10\/Transistor-Experiment-Final.png?resize=329%2C424&ssl=1\")
<\/a><\/p>\n<\/code>
\n<\/code><\/p>\n","protected":false},"excerpt":{"rendered":"