I have a 3D printed sign that I'm trying to illuminate with 24vdc LEDs, and I'm looking for a means by which I can switch the supply to each segment on and off without a very loud relay. My latest attempt was to use a MOSFET board, but I don't think I got the results I wanted. Is there a quiet mechanical relay array on the market, or is there a good way to switch, say, 500mA of 24vdc?
My apologies if this has already been covered in a previous question--I did look and search, so I did do my due diligence.
Let me guess, it was a IRF540 MOSFET module? Which is not a logic level MOSFET so will not turn on fully with an Arduino output.
A mechanical relay cannot be directly controlled by an Arduino output. It needs a driver and that driver is usually a transistor (MOSFET or BJT). So in order to get your relay to work you have to get a MOSFET (or BJT ) transistor to work with the Arduino, anyway.
The MOSFET should work (if it's a logic-level MOSFET and it's wired correctly, etc.), but there are solid state relays. Just make sure to get one that's rated for DC. Most AC & DC solid state relays are not interchangeable.
In order to get the most brightness I can, I'm powering the sign with 24vdc power, and have a power supply to convert to 12v for the arduino board.
the mosfet board I'm wanting to use as a power control relay array are two of these:
On the power side of these arrays, I'm supplying 24v to all of the OUT+ pins and connected the OUT- to the positive wires of the LEDs; the negative wires are all connected to 0vdc.
On the control side, I've connected the Arduino Uno pins 0-5 to the PWM pins of six of the eight total channels; connected all the GND to 0vdc.
I tried using this MOSFET board because the SSR array board I bought did not switch DC voltage. Upon further reading (I am a novice I should mention), I read that SSRs only control AC loads, not DC loads.
I'd be thrilled to be mistaken on that point, however, and just use an SSR relay that's designed to switch DC voltages. if you could point me in the direction of an arduino or similarly formatted board, I'd be in your debt.
Before you buy SSRs - Usually MOSFETs are switched on the ground side so NORMALLY the +Voltage would be "permanently" connected and the ground-path goes through the MOSFET. The documentation for that board may not be complete.
Here are some solid state relays. Some can switch AC and some DC. The little one in the DIP package works with both, but it needs a current-limiting resistor on the built-in opto-isolator input. The external resistor means you can use almost any control voltage (including 5V) as long as you calculate the correct resistor.
(Click on this space if Amazon is playing silly beggars!)
Power goes to "DC+" and "DC-". LEDs connect + and - to "OUTn+ and "OUTn-" respectively. Since all the positives are connected together, you can connect the positive of all the LEDs and the FET board - that is critical - to your positive supply, "DC-" to the negative of your supply and the individual "OUTn-" to the negatives of you LEDs.
If you want PWM, you have to use the pins marked "~" on the UNO. If you don[t want PWM - and presumably you do not - then use pins 2 to 7, not 0 or 1.
All the positives are common, the negatives of the LEDs go to the "OUT-" pins (that's why they are marked "-") and "DC-" is the negative of the supply. The mixed-up connections the OP describes could not work at all.
