Accessories

DIY flat panel

Thursday, August 14, 2025

Many amateur astronomers are discovering that building a DIY flat panel is an affordable and effective way to automate flat frame calibration, integrating seamlessly into ASCOM workflows with just an ESP32, a MOSFET, and a standard LED tracing light.

Astrophotographers are constantly innovating to improve their imaging workflows, often creating custom tools that rival commercial products at a fraction of the cost. One clever example comes from a maker who modified a standard LED tracing panel to function as an ASCOM Alpaca-compatible flat panel calibrator. The result is a low-cost, smart device that can automate flat frame acquisition using open-source firmware and basic electronics. For those with minimal soldering experience and access to a 3D printer, it offers a rewarding path to automation.

DIY flat panel: A smart ASCOM-compatible build for astrophotographers

The origin of this DIY flat panel project came from necessity and curiosity. The creator had previously automated flat panel shutters for their main telescopes but still used a basic USB-powered tracing panel for an older RC8 scope. After discovering the panel’s USB port and PCB had been exposed due to a crack, they realized how simple the internal wiring was, just two leads from a controller board to the LED matrix. This sparked the idea: why not swap the original controller for a smarter one using an ESP32 microcontroller?

With nothing else pressing on the schedule and some help from Claude.AI, the project quickly took shape. The goal wasn’t to build a motorized cover device, but rather to control the brightness of the panel remotely via software, letting a PC take care of exposures without touching any buttons. Within two days of coding and testing, a fully ASCOM Alpaca-compliant firmware emerged, controllable from a web interface, ASCOM driver, or serial commands.

One of the strengths of this project is its simplicity and affordability. The most expensive component is the LED tracing panel, which can cost around $15 to $20 on Amazon. The rest, an ESP32 board, MOSFET, a few jumper wires, and optionally a 3D printed shroud, can be sourced from typical maker supplies or ordered online for less than $5 to $10 combined.

To begin, the user must gently extract the original PCB from the LED panel. The two wires originally feeding the panel are rerouted through a MOSFET board. The ESP32's GPIO pin 4 is connected to the gate of the MOSFET, while the ground and power lines are wired to their respective sources. Importantly, the LED panel should draw power from an external 5V source, not directly from the ESP32, which can’t handle the current load.

Once wired correctly, the ESP32 is flashed with firmware available on GitHub (github.com/smartc/flat_panel). The firmware sets up ASCOM Alpaca functionality, a web server, and serial interface for configuration and control.

The firmware supports a range of features focused on flat panel calibration only. While it doesn’t implement motorized cover controls, it provides all essential flat panel commands using the ASCOM Alpaca CoverCalibrator interface. Users can turn the light on or off, adjust brightness with 10-bit PWM precision, and configure settings via an onboard web interface or serial terminal.

Once flashed, the ESP32 starts in AP (access point) mode if no WiFi credentials are present. The user connects to the “FlatPanelCalibrator” network, navigates to a local IP address in the browser, and inputs their home WiFi settings. After reboot, the device connects to the LAN and is reachable via its IP address for normal use.

From there, the interface provides tabs for quick brightness adjustments, deeper configuration, and network settings. It also allows setting maximum brightness limits, renaming the device, and toggling debug output for troubleshooting. This gives users a lightweight and elegant way to manage calibration routines, especially at the end of an imaging session.

Perhaps the most impressive feature of this project is its ASCOM Alpaca compliance. For astrophotographers using Windows-based tools like NINA, Sequence Generator Pro, or Voyager, the panel can be detected and managed just like a commercial calibrator. It supports automatic discovery using UDP broadcast and runs its ASCOM HTTP API on port 11111.

ASCOM methods implemented include CalibratorOn, CalibratorOff, Brightness, and MaxBrightness. Cover-related methods like OpenCover and CloseCover return a NotImplemented error, as expected. The CalibratorState function correctly reflects whether the panel is active or not. Clients simply point to the device IP and port and select device number 0 under the CoverCalibrator interface.

The firmware also includes an HTTP REST interface, allowing direct API calls to control the panel outside of ASCOM. This is useful for integrating into custom scripts or mobile apps. Developers can issue GET or PUT requests to endpoints like /api/v1/covercalibrator/0/brightness or /calibratoron.

For those who prefer to work over USB, or during initial testing, the firmware provides a robust serial interface at 115200 baud. Both text and legacy bracketed commands are supported. Users can turn the panel on with ON, off with OFF, or set brightness with BRIGHTNESS 75. Commands like STATUS and DEBUG ON help during setup and diagnostics. The dual interface (web and serial) ensures flexibility whether you're in a field observatory or at home.

The developer included a comprehensive troubleshooting section to handle common issues. If the panel doesn’t respond, users are advised to check WiFi credentials, verify serial communication at 115200 baud, or inspect wiring to the MOSFET. Flickering typically means insufficient power supply current, and dim output can often be fixed by adjusting the maximum brightness setting. For serial issues, installing appropriate USB drivers (CH340 or CP2102) may help.

The firmware is open source under the MIT License, encouraging users to contribute or adapt it to their own needs. Advanced users could even modify the firmware to add touchscreen controls, motorized shutters, or thermal monitoring.

While the panel hasn't yet been tested under starlight, it passes ASCOM Conform Universal tests and communicates reliably with PC software. The creator can monitor and adjust light levels remotely, letting automated imaging sequences run overnight without human intervention. Once set up, the panel becomes another seamless part of the imaging rig, something that just works in the background.

This project serves as a perfect example of how affordable DIY solutions can rival commercial gear in performance and integration. Astrophotographers with a bit of soldering skill and some time can add real value to their imaging workflows without breaking the bank.