Let's Make Robots!

Power for the TI LaunchPad

 

Power for the TI LaunchPad can be supplied via the USB connector. The USB power is +5V. Apparently the onboard FTDI chip converts the 5V to 3.3V for the MSP430 microprocessor. The micro power is 1.8 to 3.6V.

I'm planning a home-made shield for the LaunchPad, and I will need more than just the 3.3V for motors, servos, sensors, etc. The 3.3V from the FTDI is very current limited anyway.

So a 5V Low Drop Out (LDO) regulator will be included. When I'm running off batteries, I will also need a 3.3V source for the micro. I considered a 2nd 3.3V voltage regulator, but then I found this article on Connecting a Parallax PIR Sensor module to the LaunchPad, by suspended-chord.

He pointed out that the LaunchPad has several tie points, including TP1 and TP3. They are located need the USB connector. He writes:

"TP1 is connected to VBUS (USB's Voltage, which happens to be 5V), and TP3 is connected to the USB's GND."

So I'm going to try populating my shield with just a 5V regulator, and running the 5V from that to TP1/TP3. I just have to be careful to switch off my battery power before connecting the board to USB, so I don't have two sources trying to run to the board.

I don't know if this will work, and I hope I'm not going to damage the board somehow. If everything goes smoothly, I'll have Vin (battery power) and regulated 5V available on the shield, and 3.3V for the micro and anything that needs it.

Fingers crossed.

 

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I think I have decided how I want to power my LaunchPad shield.

I will include both 3.3V and 5V LDO regulators on the shield, and two power switches.

SW1 will be a DPDT switch that will connect Vin (from battery) to the 3.3V regulator on one pole. The other switch pole will connect the microprocessor to the 3.3V regulator power. When this switch is in the "off" position, it will connect the microprocessor to the 3.3V from the FTDI chip on the LaunchPad. This way, I will never have both 3.3 power sources connected at the same time.

SW2 be a DPDT switch that will connect Vin to the 5V regulator on one pole. The other pole of SW2 will connect Vin to some tie points on the shield, where I will allow stuff to run of unregulated battery power.

I plan to have three banks of I/O pins. Each bank can select whether they run on 3.3V regulated, 5V regulated, or Vin unregulated power.