Use an NPN transistor to switch the ground side. I've used TIP120, N-Channel MOSFETS, and even 2n2222. Works great.
Tech note on uber-cheap constant current driver from LM317: http://www.onsemi.com/pub_link/Collateral/AND8109-D.PDF
Use an NPN transistor to switch the ground side. I've used TIP120, N-Channel MOSFETS, and even 2n2222. Works great.
Tech note on uber-cheap constant current driver from LM317: http://www.onsemi.com/pub_link/Collateral/AND8109-D.PDF