| Electronics > Beginners |
| How to wire this setup? |
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| MarkF:
--- Quote from: Youkai on May 16, 2018, 07:50:18 pm ---OK so I switched to NPN transistors and the circuit works now; at least the Red, Green, and Blue light up correctly when the Arduino tells them to. New problem though. The LED are SUPER dim. Also they are the same brightness whether the 12v supply is plugged in or not. The Arduino is using USB from the computer for power right now. So I guess that for whatever reason only the Arduino voltage is getting through. --- End quote --- From your last drawing, the 2N3904 transistor are wired backwards (emitter and collector swapped) and you are missing a bunch of grounds. See attachment #1. --- Quote ---After a short web search I found this but I don't really understand it. https://electronics.stackexchange.com/questions/152960/bc547-bc548-with-5v-at-base-cant-control-12v-at-collector-emitter --- End quote --- The circuit referenced to is to turn on and off a 7805 regulator. Not really what you are trying to do. But, Q1 is acting like a high side switch and R2 pulls the base high to keep the transistor turned OFF (its normal state). Q2 is used to pull the base of Q1 low and turning it ON when a high signal is provided to the base of Q2. However, R1 should not be there and there should be a current limiting resistor is series with base of Q1. See attachment #2. |
| james_s:
I couldn't tell how the transistors are wired based on that schematic since the arrows are not shown, but for NPN you do want the emitter tied to ground and the collector to the load. |
| Youkai:
Attached is the most accurate diagram I can draw of my current test circuit. The LED is on the collector side of the transistors; ground on the emitter. The 3 grounds joining is all three going to the same rail in my breadboard. The Arduino is powered by USB so both the +V and GND are coming from the USB cable. The LED is powered by my wall outlet which is going to the +V and GND rails on the right hand side of the breadboard. In the picture of the breadboard the jumper wires are the color of the LED they are powering. From the left is the arduino pins. The short loops are the Emitter-to-ground. From the right is the cathodes of the LED strip.The Yellow/Black next to each other are +/- from the wall respectively. The black wire slightly lower in the positive rail goes to the LED common annode. Hopefully these two pictures will help you determine what my issue is. Thank you. |
| MarkF:
Your circuit should look like attached. * Looking at your breadboard picture, the emitters and collectors are swapped. * The Arduino GND and the 12V GND should be connected together. Your 12V supply IS isolated? Correct? * How many LEDs of each color are you trying to drive? Each LED will drop somewhere in the 1V to 2V range depending on the color. Driving them with 12V, you will only be able to drive about 6 LEDs of each color. I'm assuming the LEDs in the strip for each color are connected in series. I can't tell from the spec sheet. * You will need a resistor in series with the collectors to limit the current for each LED color. To obtain the same brightness for each color, they will be different values because the volt drop across each LED will depend on its color. * If you want to drive more LEDs, you will need a higher voltage with appropriate current limit resistors. |
| MarkF:
Guessing from the picture of the strip, the current limit resistors (R4, R5, R6) are part of the strip for each group of 3 and you don't need them in your circuit. Each group of 3 would be in parallel and multiply the amount of current required to drive them. |
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