4.d. General-Purpose Voltage Dividers and MOSFET Circuits

m3pi general-purpose 2/3 voltage dividers and MOSFETs with schematic diagrams.

The m3pi expansion board has four general-purpose 2/3 voltage dividers that can be accessed by the set of four upper “HV” and “LV” pins (pictured to the right) located between the Wixel and XBee socket pins. These voltage dividers can be used to safely connect 5 V outputs to 3.3 V inputs (the Wixel and XBee do not have 5V-tolerant pins): connect the 5 V signal to one of the four HV pins and then connect the corresponding LV pin to the Wixel or XBee 3.3 V pin of your choosing. The voltage dividers are not connected to anything by default.

The expansion board also has two general-purpose MOSFET circuits that can be accessed by the set of two lower “HV” and “LV” pins (pictured to the right) located between the Wixel and XBee socket pins. These circuits can be used as inverters, level-shifters (e.g. to convert a 3.3 V Wixel output to a 5 V signal), or for driving larger loads (up to 200 mA) than you can with a Wixel or Arduino I/O pin alone (e.g. high-current LEDs or relays). The MOSFET circuits are not connected to anything by default. The circuit incorporates a BSS138 MOSFET (N-channel, 50 V, 200 mA, 1.5 V maximum gate threshold voltage).