diff --git a/src/qcam/main_window.cpp b/src/qcam/main_window.cpp
index 8dbe597e7aa2..d3fedce20a9c 100644
--- a/src/qcam/main_window.cpp
+++ b/src/qcam/main_window.cpp
@@ -5,6 +5,7 @@
  * main_window.cpp - qcam - Main application window
  */
 
+#include <cmath>
 #include <iomanip>
 #include <iostream>
 #include <string>
@@ -247,6 +248,13 @@ void MainWindow::stopCapture()
 	config_.reset();
 }
 
+int SineBrightness(Buffer *buffer)
+{
+	unsigned int millisec = buffer->timestamp() / 1000000;
+	constexpr float rads = 2 * M_PI / 180;
+	return sin(0.036 * rads * millisec) * 100;
+}
+
 void MainWindow::requestComplete(Request *request,
 				 const std::map<Stream *, Buffer *> &buffers)
 {
@@ -281,6 +289,12 @@ void MainWindow::requestComplete(Request *request,
 		return;
 	}
 
+	/*
+	 * A demonstration control, which has a distinct visual effect.
+	 * Scale the brightness up and down with a sine wave.
+	 */
+	/* How do we deal with max/min/defaults etc? */
+	request->controls().emplace(ManualBrightness, SineBrightness(buffer));
 
 	request->setBuffers(buffers);
 	camera_->queueRequest(request);