If you decide to drive down from Bangalore , take the Hosur Road towards Krishnagiri. At Krishnagiri follow the Vaniyambadi / Chennai sign which takes through Nattarampalli town and Barugur. At Vaniyambadi turn on to the road leading to Tirupathur. 7 Kms from Vaniyambadi is Ponneri, the juncture at which you turn left and start climbing the ghat road consisting of 14 hair pin bends to reach Yelagiri.
If you take the train cabs are available from Jolarper to Yelagiri.
Yelagiri is at just about 150 kms from Bangalore and its best to use own vehichle to visit Yelagiri. If you have to use public transport Jolarpettai Jn is the nearest rail head near Yelagiri. There are very few direct buses to Yelagairi from Bangalore