An Ancient control panel is a device which the Ancients used to control certain technologies.
The device looks like a large table made of stone. On the upper side several large stone tablets are located, each of them containing Ancient writings. By pressing these tablets in a certain order, combination or depth, the associated technologies can be activated and controlled.
The first such device discovered by SG-1 was located on P4X-639, where it was used to control the Time loop machine on the planet. If the machine was activated, the tablets would move up and down. (SG1: "Window of Opportunity")
The next control panel was found on Dakara, this time associated with the superweapon located on the planet. SG-1 used the tablets to reprogram the energy weapon so that it would send out a massive anti-Replicator wave. (SG1: "Reckoning, Part 2")
The currently last known device was located on Camelot where it was located inside Merlin's library. This device controlled the Holographic guardian which protected the technology there and it was also used to beam in a large treasure which Merlin hid there. (SG1: "Camelot")