The Yantra Gayatri is
"Yantrarajaya Vidmahe Mahayantraya Dhimahi Tanno Yantrah Prachodayat."
The gopala-mantra (klirit krsnaya govindaya gopijana-vallabhaya svaha).

In the Chdndogrda Upanisad
Prajapati (Lord Brahma) meditated on the nature of the Universe (vishva).
He thus realized that the three planes of material existence
are prthivi (physical), antariksa (mental), and svarga (spiritual).
These three planes are thus represented by the mahd-vgdhrtis:

bhuh, bhuvah, and svah.
The seed of the Rig Vedais bhua,
the seed of the Yajur Veda is bhuvah,
and the seed of the Sama Veda is svah.

These three bijas (mahavydhrtis) are said to have been derived from OM as three primary colors are contained in a ray of white light. Prajapati came to the realise that "OM" pervades all sound. Therefore the rshis (sages) have concluded that OM (the seed) is to be uttered at the beginning and the end of brahma-gagatri. Om, when uttered at the beginning and end of brahma-gayatri, is the Vedic standard by which one should perform gayatri japa (gayatri repetition). When the personified form of Brahma gayatri is manifest she appears with five faces. These five faces correspond with the five principle features of the brahma-gayatri: