PG31 GPS RS232 Dev Board
Getting information from your project to your computer can be difficult at first. Once you discover how to setup an RS232 connection, it's really just cut-and-paste for future projects.
In this project we demonstrate how to:
- Setup 3.3V to RS232 circuit
- Setup an external power supply
- Simple PG31 GPS footprint
First we will start with a simple adjustable voltage regulation circuit:
And here is the schematic:
Now let's discuss what's going on here. The barrel jack (J1) is a basic 5.5mm OD 2.1mm ID type jack. We get an unregulated 9-13V out of the wall wart.
The D3 large diode MBRA140 is for reverse protection. It can handle up to 1A and prevents damage to the board if a center-negative wallwart is attached. This diode will cause a ~0.5V drop from whatever the wall-wart is outputting.
C2 (10uF Tantalum Capacitor in this case) is a basic decoupling cap. 10-100uF is adequate but should be rated for 15-25V.
U1 is the LM317 (or LM1117 in SMD form) adjustable voltage regulator. It will take in some larger voltage and output a set voltage. The output voltage is set with two external resistors. R1 is historically 240 and value for R2 is different for different required output voltages. In our case, we want 3.3V out of the regulator, so R2 is set to 715. The LM317 is good because it is variable, the SOT-223 package is nice becuase it can take a relatively large voltage on the input (25V max I believe?) and has decent heat dissapation.
C1 and C3 are decoupling caps that help clean up the output transcients and noise.
J2 is just a two pin polarized header so that you can either 'steal' 3.3V from the board to power other boards, or have other boards power this board without the need for the external wall wart.
So we've got a nice clean output of 3.3V from the regulator, let's look at the RS232 connection:
SFE Footprint Library
FP Name: 5-LEAD DD PAK
Linear part # :
LT1528CQ (5-DD SMD Package)
LT1528CT (TO-220-5 PTH Package)
Digikey part # : LT1528CQ-ND
Single Piece Price : $7.13
Original Creator: --Sparkfun 22:18, 25 January 2006 (PST)