Need help with simplifying a circuit for an LED sign.

Hi everyone, long time no see! I am making my friend an LED sign and I feel like my circuit is too unnecessarily complicated (as usual).

The circuit is modified from a headlamp ( and I am using it to drive transistors to then power LEDs.

The direct output on the circuit is from MOSFETs (A1SHB MOSFET Datasheet pdf - Power MOSFET. Equivalent, Catalog). I am just feeding the output into 1k resistors to power the bases of my 2n2222a transistors.

Many LEDs will be used (probably around 500ma maximum for each "mode" as you will see later). In my schematic I just put in one LED per mode but in reality it will just be a bunch of LEDs with resistors connected in parallel, so I didn't see a reason to put them all in.

The way I designed the circuit requires me to use common anode LEDs for the main part of the sign, but if any simplifications use common cathode LEDs that would be ideal, but not required.

The main two colors are orange and pink so the point of my circuit is to have the red part of the common anode LEDs on whenever the circuit is on, and then it just switches between different patterns of blue and green to create pink and orange.

I also have a video showing my modification (the first circuit tested) and then the one straight from the headlamp as a comparison (the second circuit tested). I don't have common anode LEDs right now so I just used individual LEDs while still turning on the correct color.

For some reason one of the blue LEDs (The one at the top of the blue breadboard) was pretty dim even though it has its own separate resistor so I'm not sure what that's all about.

As always, I greatly appreciate any help, and let me know if I can explain anything better. Thanks!



Your description rambles a bit.... Are you sure the LED draws enough current for the transistor to be fully turned on?

What does the sign do? It may be easier to use ws2811 LED modules. No transistors, no resistors.

Looking at the circuit I see multiple 2N2222's in parallel without a current sharing resistor, not the best configuration.

I would dump the 2N2222's and get a mosfet that can replace the paralleled 2N2222's in one device.

Hi! Sorry about the description, I'll change it in a little bit. I believe the LEDs are drawing enough current because all of the other LEDs are lit up how they should be. It might be the forward voltage, but that doesn't make much sense because the other blue LEDs are working. Its a mystery.

The sign has 3 main modes, with the other three modes just changing the main modes through either dimming them or making them blink.

The first main mode looks like this:

The second main mode looks like this:

The third and final main mode looks like this:

The headlamp module is just used to change between modes. I would prefer not to use the ws2811 because I want this project to be simple in that I don't want to use an Arduino. Also, the letter spacing is pretty tight on the actual sign, so the way I would use my LEDs would make sure light from one letter doesn't hit the next. Hope that helps.

EDIT: What MOSFET would you recommend? The parallel configuration is so that the pink heart stays on during every mode. It is also used to turn on the red part of the rgb LEDs for every mode. And do you think transistors are needed at all? For the current part of things they might be but I feel like diodes could be used to switch on and off the different LEDs.

Are not Q7, Q8 & Q9 in parallel? As well as Q4 & Q5?

What voltages are the two Vcc? They can't be the same 3v3. You should not use the same name for two different voltages, not good form.

Yes, there are three networks that have parallel outputs, but different base inputs: Q7, Q8, and Q9 are in parallel. Q4 and Q5 are in parallel. Q2 and Q6 are in parallel. Also, both Vccs are the same 3v3. I have the ability to also use 5v, but the headlamp circuit used a lipo battery with a maximum of 4v2 and I didn't want to risk using 5v so I just used 3v3 instead. That being said, If the transistors need 5v I can give them that. I am using this 800ma max buck converter to get the 3v3 out of a 5v usb supply.

@JohnRob: Those transistors are not in parallel. They have different
base drive signals.

Missed that :frowning:

Then one transistor can be used with a steering diode for each different base drive?

Ya I was thinking about that. Instead of having three transistors could I have only one but then use three diodes so that when the mode changes, each diode could activate the base of the same transistor.

I'm not an expert in this subject, but each control output (M1, M2 & M3) is used to switch 3 transistors through a base resistor of 1K. If either of the tree R1K resistors is slightly off (higher) than the other two then the transistor might not get fully saturated / opened.

If only focusing on M1, I would remove Q1+Q2 and their base resistors (R11 + R12) and attach the cathode/- of all three LED's to the collector of Q7. 2N2222 will handle 600mA, so that should not be an issue.

I can't really do that because then the LEDs that you are suggesting I attach to the collector of Q7 would only be on during mode one. The reason I used three transistors was to turn on the LEDs for every mode. As we were talking about a little back, I might be able to use diodes to turn on one transistor for every three modes.

I might be able to use diodes to turn on one transistor for every three modes.

I considered diodes but I didn't see the benefit of replacing a transistor with a diode. And you have to be a little careful because you would have to deal with the transistor Vbe drop and the diode drop.

Ya, thats true. It would only cut down the parts needed by a little bit. I don't think the Vbe would be too much of an issue, but I don't know if there is actually a very good way to simplify the circuit. Sure, a couple things could be done, but do you think there is a way to make it much less complicated?

We don't know what that driver is. If you didn't have to "decode" the signals you could minimize the circuit a bit more.

Ya, the driver, of course, isn't labelled so that other companies can't copy it. I'll keep thinking. Thanks for your help so far!

I would prefer not to use the ws2811 because I want this project to be simple in that I don’t want to use an Arduino.

Good thing that you aren’t asking this question on an Arduino forum.

Lol, that is a perfect-one liner. I don't know why but that cracked me up. Anyways, I completely understand that technically this is the wrong place to ask, but I have gotten a ton of help here before and I know that you guys are skilled electronic geniuses, so I figured I would ask. I greatly appreciate any help that is given, so thanks so much even if this is the wrong place to ask.

Don't feel bad, the topic is "General Electronics" we all knew either there is no arduino or the arduino is not related to the question.

I don't know about the others (although I expect they feel the same as I) I do this because it makes me feel good to help others. I have no love nor hate for the arduino. I started using them because the boards were so available.

Alright, thanks. Aside from Google and YouTube, this is the first place I go when I have an issue, and I have always gotten help so I have deemed it a very reliable place. My question this time is a little harder because there’s not a whole lot that can be done (as far as I know), but I know we’ll come up with something.