Brett's Build Log » schematic

First USB Power Shield Prototype on the Way!

brettinman — Thu, 25 Jun 2009 01:52:06 +0000

After toying with the relays and Arduino I found that the diodes weren’t necessary – especially since the relay is latching, and current will be flowing both ways, so putting a diode in each direction would just create a short.

As such, I made some modifications to the board and put it into Gerber files using Eagle, uploaded them to BatchPCB, and am now waiting for the first one to arrive so that I can populate and test it. In the meantime, I need to get around to packaging the WootOff software for distribution, and come up with some documentation of this project that’s more readable than this series of blog posts.

Here’s the board schematic of the Prototype board:

USB Power Shield v1.0 - Prototype

USB Power Shield

brettinman — Thu, 11 Jun 2009 04:33:05 +0000

I really wanted there to be a complete solution for the Woot-Off lights project that could be almost plug and play for the end user, so today I drew up a schematic and a board for a USB Power Shield for the Arduino. It pops onto the Arduino like any other shield, and by controlling pins 9-12, you can control power to four devices.

There are two USB ports for anything that takes USB power (5V) – of course, these ports are for power only (no data). You can use these to control the Woot-Off lights without cutting and soldering the cord, and something else (USB Fan? Light? Humping Dog?). There are also four pads toward the middle so you can solder in anything else that takes 5V power.

USB Power Shield board

Schematic here.

Since the Arduino can only supply maybe 300mA while on USB power and 600mA from its small 5V regulator (using DC in), I’ve included the stuff necessary to add a 7805 regulator and related components to allow up to 1A (if you use a heatsink). You can always leave these pads empty if you don’t plan on using that much power. The Woot-Off Lights will need at least the 5V regulator on the Arduino. There are also LEDs to show if the regulator and board itself are powered – these can be omitted as well.

The board uses four 2N3906 to control power of up to 200mA at 5V to four devices. By writing the corresponding pin LOW on the Arduino, you turn on the transistor and allow current to flow from 5V to the device (and then, hopefully, out to GND). Very Simple.

Woot-Off Lights Schematic and Hardware

brettinman — Tue, 19 May 2009 05:58:18 +0000

Here’s some details about the hardware setup for the woot-off lights. It’s exactly as I described in the first post – this just includes the schematic and goes a little more in depth.

Quick and Dirty Schematic for Woot-Off Light Control

Let’s take it from left to right. USB input to the Arduino to send serial data. The current from the USB port is not sufficient to start the motors (they require a bit of boost when turned on and consume less current during normal operation), therefore we use the DC input on the Arduino board to supplement the USB. Feed it somewhere between 7-10V (up to 12V should be fine). The Arduino contains a regulator to lower the Vin down to 5V.

The 5V is then connected to the V+ of the lights (red wire). The GND of the lights is connected to Pin 18 of the ULN2803 IC. The ULN2803 also has it’s own 5V/GND connections (the 5V connection is necessary in this application because of the inductance of the motors). When the ULN2803 receives a HIGH input on Pin 1 (coming from Pin 9 on Arduino), it connects Pin 18 to GND (note that this is the same for all pins on the IC except 9/10 – i.e., Pin 2 controls Pin 17, etc). Thus, the lights are now fully connected to both 5V and GND, the circuit is complete, and we have spinny lights.

Work continues on reading a Woot-Off Tracker from a C++ application – if anyone has tips or ideas, they’d be appreciated.