power on the propeller project board

dr hydra

I am so confused about the power on the project board...if I use the power input and used a regulated 5V source...then the VIN header will be 5V regardless... if the board is plugged into the USB port? Also, I can still program the board through the USB port while it is getting power through the power input (VIN)..is that correct(therefore, two power sources)? The reason I am asking is because I need to use a microcontroller that is 5V with my propeller and I need to make sure that I can power both chips safely. Or is it possible to power both chips (5V and 3.3V) from the USB power? The 5V microcontroller is a ATMEGA1284.

Publison

dr hydra wrote: »

I am so confused about the power on the project board...if I use the power input and used a regulated 5V source...then the VIN header will be 5V regardless... if the board is plugged into the USB port? Also, I can still program the board through the USB port while it is getting power through the power input (VIN)..is that correct(therefore, two power sources)? The reason I am asking is because I need to use a microcontroller that is 5V with my propeller and I need to make sure that I can power both chips safely. Or is it possible to power both chips (5V and 3.3V) from the USB power? The 5V microcontroller is a ATMEGA1284.

Per the user manual (Ver 2.0)

(8) USB Port This port provides a virtual serial comm port interface from your computer to the Propeller P8X32A
microcontroller. When connected it also provides power to the board’s 3.3 V switching regulator, making
it easy to connect and program without the need for an external power source. The USB connection can
supply no more than 500 mA, so if your if your project circuits connected to the 3.3 V rail require
additional current, you will need to utilize the external power input.

Power received through the USB port does not reach the VIN rail. To power circuits from the VIN rail,
you must have an external power source connected. Protection is in place to make it safe to use USB
power and the external power input at the same time. (Note: This board is compatible with USB
chargers.)

Publison

dr hydra wrote: »

Or is it possible to power both chips (5V and 3.3V) from the USB power? The 5V microcontroller is a ATMEGA1284.

The Project board does not have a 5V regulator, so if you provide a regulated power supply to VIN, you could also power the other uController from VIN.

homosapien

If I am using the PPB USB and need a 5v supply, I often solder a wire (30 ga. kynar works well) from the top of the surface-mount resistor to the right of the FTDI chip and run it to whatever needs 5v (this taps into the 5v delivered via the USB cable). Doing this allows one to use the 5v being supplied via the USB, and skip the step of adding a 5v regulated power supply to the board.

If the USB connector is connected to a computer, you need to make sure the circuits on the PPB USB will not draw more than 500mA total (3.3v + 5v). If you are using the USB connector with a 5v USB charger/wall wart, you just need to make sure that your total power usage does not exceed the rating of the charger/wall wart

(This means If your total circuit uses more than 500mA, you would need to program the PROP via the computer USB cable before you add the rest of the >500mA circuit, which could be problematic. I would only use this setup for circuits that use less than 500mA total, OR have some way to disconnect the additional 5v load if/when you need to update the PROP programming) .

If you need more details, let me know.


Nate

dr hydra

For the 5v usb...what resistor do I solder off from? Does anyone have a picture?

homosapien

This is what I have done in the past. FYI it is tapping from the top of c21, not a resistor.

Nate

dr hydra

Perfect...thank you