I've been working on a project where I want to control VGA color channels using an external 5V signal, like an envelope or LFO. I've stripped down some VGA components for this purpose, but I've hit a wall. I initially tried using an LDR, but it didn't have the needed strength. JFETs and op-amps haven't given me much success either; the JFET only added minor distortion, while the op-amp barely affected anything. The one solution that worked was using a 1k potentiometer, but I'd prefer a voltage-based control instead of manual adjustments. Any suggestions? 🙂
5 Answers
Look into some video switches; they can control whether a video signal is on or off, which might help with what you're trying to accomplish.
Keep in mind that VGA timing signals work with TTL levels, while color channel voltages should only be between 0V and 0.7V. You might need a voltage divider with a 470-ohm resistor to get the right levels for your VGA line. Overvoltage can trigger issues, which is likely why the pot setup worked for you.
You might want to consider using a Digital to Analog Converter (DAC). That could help with controlling the voltage levels more effectively.
That makes sense! I didn't think about the LFOs not being digital outputs. I'll check into DACs. Thanks!
Try wiring a MOSFET with the source to ground, the drain to the VGA signal, and the gate connected to a positive DC voltage from a pot. Just be aware that getting smooth control could require a feedback setup.
You might also need a pull-up on the drain to stabilize the signal.
Definitely make sure your components can handle the right current. If you're sourcing current from a power supply, aim for less than your supply voltage divided by 75 ohms to stay safe.
I managed to switch it on and off, but I'm looking for voltage control, much like adjusting volume on an audio signal.