Tuesday, April 16, 2013

Power supply for my robot

Tonight's project, a power supply (DC to DC converter) for my robot project. It must be able to power a USB hub. The hub in turn powers the Raspberry Pi Model A, WiFi dongle, a Webcam, and an Arduino board. The power supply should also provide power for the H-Bridge and motors.

The Arduino itself directly powers the servo, IR sensor, Sonar, Electronic Compass, and perhaps a 433 MHz radio.

The 7805 is rated for 1 Amps, I've got a resetable PTC fuse rated for 0.3 Amps, but I think I will replace it with a fast 1A glass fuse. I will also have 1N4001 to make sure the batteries are placed the right way, a LED to show power is on, and a on/off switch.

Power supply in parts
The parts list

  • Perfboard PCB
  • DC connector
  • Fuse holder
  • 1 Amp fast fuse
  • 220 uF electrolytic capacitor
  • 10 uF electrolytic capacitor
  • 2.4 KOhm resistor 
  • Green LED
  • 7805 1 Amp 
  • 2.1 mm DC plug (for the USB hub)

Powersupply for my robot, First LED test
Connected the power-supply to the hub. And the hub powers the robot and the Raspberry Pi
When trying to boot the RPi from 9V battery the Pi reboots directly after the colored splash screen indicating that the single battery cannot provide the requested amount of power:

"Immediately after displaying the splash screen, the PI starts consuming a little more current, if the PI resets at that moment its an indication that the power supply isn't able to deliver the full current your PI requires" - R-Pi Troubleshooting
Image from http://elinux.org/File:Debug-screen.jpg

When connecting the powersupply to a battery-eliminator that can provide more current the pi boots up fine, so it is the single nine volt battery that is the source of the problem.
Robot batteries on the underside
I connected it to the 6 AA battery pack on the underside of the robot and it booted up fine... Epic win!

Pi running and booting fun from the 6 AA batteries

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