Review before production on RP2350 MIDI-To-Light Circuit - Page 1
Forum section: electronics / projects

author: chros
author_rank: Newbie
timestamp: June 12, 2025, 12:19:07 pm
content: Dear Community,once more I'd like to seek your expertise and knowledge to check on my recent project a MIDI-to-Light Circuit using a RP2350A microcontroller. The purpose of the circuit is, to listen to the MIDI traffic and based on the data to light up an 12V LED RGB Strip with a common anode and individual cathode for each RGB-color.The device can be added into a MIDI chain and forward the received MIDI signals via a MIDI THRU port. Additionally to the 5-pin DIN connector, a second MIDI THRU port using a 3.5mm jack plug can be soldered onto the board, adding a MIDI-Splitter function. Using jumpers on two 3-pin-header, theMIDI-typeof the jack plug can be switched between TRS-A and TRS-B mode.I am using the RP2350A as microcontroller as I am quite familiar with the former RP2040 and I would like to try out the updated version. I have carefully checked theHardware Design Guideand theDatasheetsection 6.3.8 concerning "External Components and PCB layout requirements" of the RP2350 Core Voltage Regulator. Anyhow, a second look won't do any harm.The PCB has a dimension of 58mm by 74mm and is a 4-layer board with the following layer stack:Top: Components and SignalInner 1: GNDInner 2: +3V3Signal (no components)I tried to design the circuit robust in a certain manner. The intended input voltage via the LV Power Plug is +12V. Anyhow, the buck converter is able to work in a range from ~4V to 32V. An analog feedback allows the microcontroller to check the supply voltage and en-/disable the p-MOSFET to power the LED RGB Strip.As "user interface" I am using the round LCD display GC9A01A with a resolution of 240x240 pixels. The display will be mounded into a housing which I still have to design and 3D print. Meaning no holes on the PCB are foreseen to mount the display. A rotary encoder is used to configure the device without connection the circuit to a computer via USB.The schematic can be found here:Schematic_RP2350-MIDI-Lighter(All components marked with a red "DNP" (Do not populate) will not be assembled by the assembly service of my choice)Below, find pictures of the PCB Layout:(Top Layer)(Bottom Layer (not mirrored))(Top and Bottom Layer plus indicted position of the display)(Cutouts of the inner layers for the RP2350 Core Voltage Regulator)(Photo View Top Layer)(Photo View Bottom Layer (mirrored))There are two points I consider to update in the circuitry:The p-MOSFET (U10) to power the LED strip is a simple unprotected MOSFET. I consider to replace this IC with a "Smart" High-Side Switch including overcurrent and thermal protection. The PCB fuses do not protect against short-circuit of the LED Strip and currently there is no way of detecting any issue.The switch of the MIDI-types from TRS-A and TRS-B has to be done manually setting two jumpers on pin headers. This requires opening the housing, setting the jumpers and closing the housing again. I wonder, if there is some kind of transmission gates or some other kind of circuitry I could use to set the MIDI-type via the RP2350? As MIDI is a current based protocol, the circuitry would need to be very low-ohmic to not have any significant impact on the MIDI signal current.Anyhow, let me thank you in advance for your feedback and comments! If there are any questions about the circuit or the use case of this device, I am more than happy to answer.Cheers!