I’m creating an LED panel with both cool and warm white LEDs. I wanted each color to be dimmable, so I basically have alternating rows of cool and warm LEDs. I created a schematic that seems to pass the ERC, but I’m wondering if this schematic actually works. Shouldn’t I need a GND somewhere?
If a schematic passes ERC, it is no guarantee that it will actually “work”.
There also does not have to be a “GND” anywhere. “GND” (in electronics as a whole) is nothing more a convenient reference that is used to compare other voltages to. This has nothing to do with KiCad, it’s just one of the first things you should learn in electronics.
In KiCad “GND” is treated as a (global) label, while you have used “Source1” and “Source2” as (local) labels.
All that your schematic does is connect one side of all the led strings to pin 1 of the screw connector, and the other sides of the led strings to either pin 2 or pin 3 of that screw connector.
I also wonder why you put a “PWR_FLAG” symbol on the connector. LED pins are defined as “passive” and therefore the “PWR_FLAG” is not needed in this case.
A good source for information about various KiCad aspects is collected in the FAQ part of this forum (which you can also find in the title bar at the top).
You can for example search it for the “PWR_FLAG” symbol:
https://forum.kicad.info/search?q=pwr_flag%20category%3A19
Also: Are you sure your LED’s are in the right direction?
In the way you’ve drawn them, the voltage on the “SourceX” pins must be higher then on the “VCC” to light them up.
LED’s are diodes and current flows only in one direction (think of the triangle as an arrow pointing the same direction as the current flow) from the Anode end. The pointer end is the Cathode and goes to ground.
I think some basic homework is in order…
The Sources should be the Voltage going in and the Pointed end you have labeled VCC should be going to ground, not VCC. Sources are basically the same as VCC (if you want to think in that context)
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Or… if the sources are low active (because the driver circuit can sink more current than it can source) he needs to turn all the diodes around such that when each source signal goes low to ground (with reference to VCC) the LEDs turn on.
Without knowing the operation of the driving circuit we as a group don’t know if your solution or my solution is the correct one.
Or maybe this his schematic is right and the source signals will actually go higher than VCC… (Odd, I know. But possible.)
Hi guys-
Appreciate the replies. Yeah I know I need to do some remedial homework, I’ve mostly been learning through youtube and reading reddit posts for the past couple weeks. This is the basic idea, I’m sending a pwm signal to a couple of mosfets from a microcontroller. The positive from the 12v adapter is going to both strips, but the negative is coming from the drain of the mosfets.
My original reasoning was since the positive is coming from 12v I would just have one terminal of the connector be the Vcc, and the other two terminals would come from the mosfets. This is probably naive, I’m mostly trying to follow the physical layout of my breadboard model.
Any ideas on how I can represent this?
Why not put your ESP board and the FET’s also on the PCB?
Have you built the thing on a breadboard? 3V3 is a quite low voltage and lot’s of MOSfet’s won’t switch at all or switch unreliably.
Then also add some buffer capacitors and a voltage regulator that makes something suitable for the ESP board from the 12V supply.
Currently GND is typically the (-) of power source (in times of germanium transistors GND was typically (+) of power source).
As at your schematic to work voltage at Source1 and Source2 should be higher then at VCC it looks that your VCC will be probably connected to GND of PCB driving this one.
That means that your diodes should be reversed - my previous conclusion was form how diodes are connected.
Typical 12V while LED tape contains sections of 3 LEDs + resistor. Using 4 diodes is not a good idea. Their brightness will be very sensitive to power voltage change, and their temperature.
Yeah thats basically what I’m doing. I have the 12v power supply running through a step down converter going into the esp. I guess for the schematic I wanted to make the light panels separate so I figured I would make a schematic for the panels and then a separate one for the ESP32 dimmer. Can you generate multiple gerber files from one schematic?
As for the mosfets I had to try a bunch until I could find one that has a threshold low enough to be fully turned on by logic level voltage. Yeah I have the whole thing built on a breadboard right now, just trying to design the pcb now.
Yeah I actually should have drawn that basic idea diagram better. The original plan started with just making a bunch of LED strips wired together. But the more I read it seemed cool to try and make a panel with surface mount leds. The datasheet I read says the typical forward voltage was 2.7 so it seemed safe to use 4 in a row with a couple of small resistors.
I’m a little confused about the explanation. So are you saying the electrons are flowing from the mosfets and that source1 should be driving the LEDs? What should be on the other end then? It seems weird because I thought Vcc was always the positive side especially since its coming from the anode of the 12v adapter.
A trick you can use is to raise the “GND” level of the ESP board a bit by putting a few diodes in series in the GND lead, but you have to carefully consider what that does to the rest of the schematic (attached USB cable for example)
If you want your LED’s to light in your last screenshot, then current goes from left to right. Current through diode symbols goes in the direction of the arrow.
The electrons go from right to left and that’s not my fault.
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If you need not higher then 65mA pulses then OK.
Not from the mosfets but current flows through diode as its arrow show so at your schematic from left to right. Current also flows from higher voltage to lover so at your first schematic Source1 should have higher voltage then VCC.
Your diodes should be 180 degree rotated and everything will be correct.
No, but you can have two separate schematic at the same schematic and at the same board. Board can have any shape for example looking as two boards separated with 2mm gap with two bridges to be cut by you later (typically you use some holes in those bridges to make them being cut easier).
The first question is: what is your logic voltage 5V, 3V3 or less?
You can use for example DMG1012UW or DMN2056U.
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I forgot to answer this…
Currently KiCad is one PCB for One project.
A simple way around this limitation is to:
- Draw two PCB outlines in Pcbnew.
- Design both PCB’s.
- Save the project.
- Delete one of the PCB’s with all it’s contents.
- Generate Gerbers for the other PCB.
- Re-load the PCB from disk.
- Delete the other PCB.
- Generate Gerber files for the first PCB.
If there are connections between the PCB’s for example though connectors, then it is advisable to orient the PCB’s in a way that they are close to each other and Ratsnest lines don’t fly over the PCB’s.
Yeah I’ll prob leave the GND the way it is right now I don’t think I have the foundation to reason through the side effects of adding a couple diodes to the GND. I can follow the arrows that is a pretty good rule for current flow. Thinking about electrons flowing the opposite way at the same time is something I’ll try and understand another day though lol.
So my idea is to make a lamp with 2 panels. that are controllable through the main base (where the esp32 and the dimmer will live). I was going to make a couple for some friends too assuming it doesn’t light on fire once turned on, so I figured since the panels are square it would be more economical to put all the panels on one board and all the esp32 dimmers on the other. I like the idea of having the schematic all in one though it seems easier to visualize things.
Yeah the ESP32 runs on 3.3V. Thanks for the suggestions I’m using through hole mosfets right now so I can work with the breadboard but I’d like to surface mount in the future.
I’m going to try this out. Thanks for the suggestion.
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