Welcome back to Day 11 of 12 Days of Arduino! Today I backtrack a bit and tie up some “loose ends” with the design.
The HC-06 that I am using states that it needs 3.3v on the rx, not 5v as I had it set up yesterday. We’ll want to comply with this to avoid damaging any components. A simple way to go about this is to create a voltage divider using a couple resistors. I use this handy tool that does all the math for you to figure out what resistance resistors are necessary to get our voltage down to 3.3v: Voltage Divider Calculator. I ended up going with a 1k and a 2k resistor to obtain close to 3.3v.
Pro Tip: You won’t find this in most tutorials or datasheets, the heatsink tab of the TIP120 is directly connected to the Collector.
Because of the heat sink I had connected to both the Tip120’s, when the circuit would close it would also close the circuit to the transistor that was also connected to the heatsink. So unfortunately I had to remove the cool looking heat sink which honestly was probably complete overkill in the first place, more aesthetic than functional, so it’s probably for the best! That being said.