Servo + battery + serial & stand alone
prof_braino
Posts: 4,313
I want my prop based servo tester to run off the USB with the serial connection active;
also I want it to run standalone off of batteries.
A single USB is supposed to supply 0.5 A of current at 5 volts. (My old PC may vary)
Fluke 77 meter says the servo measures 7 mA idle, with peaks of 150 mA although the peaks are rare and average 85 mA
The prop data sheet say max draw is 300 mA
I think that:
300 mA (prop) + 150 mA (servo) < 500 mA (USB), so this should be OK.
This already works, and I can send result to the PC over USB serial with no smoke.
I also want to run off of batteries. Can I just run the battery power to Vin, or does the FDTI chip need to be disconnected or isolated? Would I have to disconnect the batteries before I plug in the USB, or is this ok? If necessary it is acceptable to swap between USB and batteries, and not allow using both at once; but I would prefer a "hot swap" option.
Also I want to use the smallest batteries possible, so I was thinking off using this 5 volt 1 farad (1F) super capacitor to run the servo. A 500 ohm current limiting resistor would limit current to charge the capacitor to around 10 mA. Does this sound reasonable? What would I have to change to make it work?
Last, I want to do this on the Quick Start board. Is my Quick Start doomed?
EDIT -
I ended up just connecting a micro servo to a a pin, Vin, and GND.
The Qucikstart works fine for checking the range an limits of the micro servo's and runs off the USB port or off a 4.8 V battery pack
also I want it to run standalone off of batteries.
A single USB is supposed to supply 0.5 A of current at 5 volts. (My old PC may vary)
Fluke 77 meter says the servo measures 7 mA idle, with peaks of 150 mA although the peaks are rare and average 85 mA
The prop data sheet say max draw is 300 mA
I think that:
300 mA (prop) + 150 mA (servo) < 500 mA (USB), so this should be OK.
This already works, and I can send result to the PC over USB serial with no smoke.
I also want to run off of batteries. Can I just run the battery power to Vin, or does the FDTI chip need to be disconnected or isolated? Would I have to disconnect the batteries before I plug in the USB, or is this ok? If necessary it is acceptable to swap between USB and batteries, and not allow using both at once; but I would prefer a "hot swap" option.
Also I want to use the smallest batteries possible, so I was thinking off using this 5 volt 1 farad (1F) super capacitor to run the servo. A 500 ohm current limiting resistor would limit current to charge the capacitor to around 10 mA. Does this sound reasonable? What would I have to change to make it work?
Last, I want to do this on the Quick Start board. Is my Quick Start doomed?
EDIT -
I ended up just connecting a micro servo to a a pin, Vin, and GND.
The Qucikstart works fine for checking the range an limits of the micro servo's and runs off the USB port or off a 4.8 V battery pack
Comments
The prop boards boot to the propforthkernel.spin forth prompt on the serial port with no problems. Does this mean that the prop boards are drawing less than 100 mA, or does the FTDI chip automagically request more power?
Also the servo was running off the same USB and showing peaks of 150 mA without reset the prop. Does this fit with the default?
Should I change the current liniting resistor to 5K?