Serial level converter board question

When using the serial level converter board http://www.sparkfun.com/commerce/produc … ts_id=8745 do you need t use R3 if the device you are connecting to has a signal on it? It looks like it is just a pullup for the low voltage side, or is it doing duty as a bias on the circuit? I’m going to be using this board with the RN-41 Bluetooth module and don’t want to fry anything. Will be shifting from the 3.3 volts of the RN-41 to 5 volts on a fuel injection computer.

Greg,

R3 ensures Q1 will turn off when the TX_LV signal goes high. I’ve run an RN-41 on one of these converters for several hours without a problem.

The only change to my converter is an extra 10K resistor bridging the RX_HV and RX_LV pins. This divides a 5v input to 3.3 volts instead of 2.5.

Jon

Thanks. I’m prototyping with the level converter and working on a board design that will fit on the bottom of the RN-41 device. Every square millimeter is precious. I’m going to scope the device it connects to and see if I even need to convert the 3.3 volt TX up to 5 volt, that would let me get away with a single 3.3 volt supply and free up a lot of room. Even with SOT-89 devices they take up a lot of space, especially when you get filtering on there too. Wish the device that I’m connecting to had 5 volts on the connector instead of the 11 to 16 that it has, it’s an automotive interface.

Sounds like you pretty much made the 10K-20K divider that the RN-41 data sheet shows.