SparkFun Forums

[ryan]

hi all
i just wanna ask do i need to add any signal level converter if i want to interface Lassen iQ Gps module to PIC microcontroller.
regards...

[sparky]

Maybe...

The Lassen iQ is a 3.3V part. Most PICs are going to be 5V parts. Get a Low voltage PIC ("PIC16LF88" for example), run it at 3.3V at a max of 10MHz and you'll have no problems.

Otherwise, if you've got a 5V micro, you'll need to step down the... Wait a minute, in most applications all you do is listen to the GPS unit (outputting NMEA data at 1Hz). If all you are doing is listening, the PIC happily connects to the 3.3V TX pin of the Lassen iQ (this will connector to the RX pin on your PIC). The CMOS threshold is 2V so that's kosher. Just don't try to have the PIC send commands to the Lassen iQ (unless you use voltage conversion).

-Nathan

[huey]

I believe that the pins used for the UART are Schmitt Trigger inputs which, if running at 5V, will require at least 4V (.0.8 * VDD) to register a '1'. You could use a open-collector buffer pulled high with a resistor to perform the level translation, or you could use a regular pin on the PIC and bit-bang the serial.

HTH,

Greg

[Philba]

This keeps coming up (I think I've said the same thing about 3 times) and I've seen Nathan say that several times. It would be great if Nathan could say what PIC UARTs at 5V he has used with other 3.3V parts. Is the microchip spec unreasonably restrictive? I keep hearing people say there is no problem but don't particularly want to design a board and discover it is a problem.