There are three headers on the JeeNode Zero: a 17-pin main header (left), a 6-pin FTDI header (bottom), and a 5-pin AUX header (bottom right):
Many - but not all - pins can support a (digital) input voltage level up to 5.5V. All output voltage levels are between 0V and 3.3V.
Power is normally applied to either of the 5V pins (they are internally tied together on the PCB). If the supply voltage is between 3.4V and 5.5V, the JeeNode Zero will run at its nominal 3.3V design level. However, with proper clock confiuration, a lower voltage can also be applied, since the µC and RF module can both work down to 1.8V.
If a 3V coin cell is fitted, power should not be applied to any of the supply pins - one solution is to always remove the coin cell when connecting to FTDI.
The top of the JeeNode Zero is unpopulated by default:
The bottom has the wireless radio module, the micrcontroller, and the power supply regulator:
The boards above are shown with the FTDI header mounted in the recommended “in-line” position, but the header can also be mounted upwards or downwards.