View Full Version : voltage levels Teensy 3.0

12-05-2012, 11:26 PM
Hello everybody. I am starting out in the hobby. I am trying to interface the Teensy 3.0 which is a 3.3V device with the BluetoothMate from Sparkfun which puts out 5V signals. The schematic of the Bluetooth device is attached. Will I need any level conversion ?

12-06-2012, 01:56 AM
The actual bluetooth module is 3.3 volts. The circuits from Sparkfun convert from 5 to 3.3 volts, which you don't need.

Probably the simplest thing to try first is just running the whole module on 3.3 volts. Just connect the VCC pin to 3.3 volts (not VIN). Odds are good it will just work?

If it doesn't, the problem is likely U3 "V_REG_LEDSMD" (no actual part number) outputs less than 3.3 volts (perhaps 3.0 or 2.8 or something) when the input is 3.3 volts. If the module really needs the fully 3.3 volts, I'd try try soldering a small wire from VCC (which is connected to Teensy 3.0's 3.3V pin) to 3.3 volts. Then the whole board will be running on 3.3 volts.

The level converter circuits are should work fine if both sides are 3.3 volts.

12-06-2012, 03:11 AM
That BSS138 level-converting circuit has served me well in the past... it originally came via Rocket Number Nine from Herman Shutter inside Phillips? I still use the BSS138 approach for interfacing single signals as the circuit is dirt simple, easy to lay out and uses inexpensive components. But it is tedious to lay out lots of components on the board as well as stocking them onto the board when the time comes for mounting and reflowing everything.

So, for collections of signals I prefer using a TXB0104-TXB0108. Like the BSS-138 circuit, these converters are bidirectional, perfect for interfacing an 5V Arduino to a 3.3V SD card holder, for example. But only three components are needed, i.e. the chip and the two de-coupling capacitors. The TXS series can be used for I2C. Adafruit sells a converter breakout board based on the TXB0108.