Mail Light – Part 1 – Hardware

March 14, 2009

Part 1
Part 2
Part 3
Part 4

The idea behind the Mail Light project is to indicate the presence of emails that are currently on my email server with a flashing LED. I am often not right at my desk and I would like to know if I have email. Or I am near my desk, but my screen saver has kicked in while I’m working on something that doesn’t involve a constant mouse wiggle. By making a little black box with LEDs that can be controlled by USB through a mail monitoring program, I can be alerted to the presence of email on my server.

Mail Light hardware under a monitor.

Mail Light hardware under a monitor.

Part 1 of this project is the Mail Light hardware. Part 2-3 of this project will be the Mail Light software.

The Mail Light hardware will be made from a U421 USB interface, a ULN2803 driver, a bit of circuit board, 8 LEDs, 8 LED mounting rings, 8 330 ohm resistors, a small plastic box, and wire-wrap wire for point-to-point circuit connections.

U421, box, LED, and LED mounting ring.

U421, box, LED, and LED mounting ring.

Diagram for ULN2803 driver.

Diagram for ULN2803 driver.

I chose a small plastic box with a black finish. Four LEDs will be mounted on one side visible from my position seated at my desk. These LEDs are bright, but not blindingly so. On the other side of this box are four very bright LEDs. These bright LEDs will be visible from my lab. I will be able to just glance into my office and see if I have email.

Outside of plastic box.

Outside of plastic box.

The inside of the box has enough room for the U421 and other parts. There will be a slot for the USB cable to exit the box. Eight 1/4″ holes will be drilled for the LEDs. The inside of the box has a little bit of extra plastic in the way.

Inside of plastic box.

Inside of plastic box.

I removed the extra plastic with the same tool I use to flush-cut component leads on a soldered board. Then I removed the bits of plastic that remained with a small chisel.

Inside of plastic box with plastic removed.

Inside of plastic box with plastic removed.

Each side of the box will have four LEDs. I drilled four pilot holes for the LEDs. After that I enlarged the holes to be one quarter inch to accommodate the LEDs in their mounting rings.

Pilot holes LEDs drilled in box.

Pilot holes LEDs drilled in box.

I used the type of printed circuit board for this project that I frequently use for prototyping things. This board is a grid of holes spaced .1″ apart.

Top of printed circuit board.

Top of printed circuit board.

On the bottom of the board are isolated copper rings – donuts. The copper should be cleaned until shiny. I used a metal brush and scrubbed in two or three directions until the copper is shiny. Then I coated the copper with liquid flux and applied solder to completely cover the exposed copper.

Bottom of printed circuit board.

Bottom of printed circuit board.

Before applying solder, I cut the board to fit the little box.

PCB cut to fit box.

PCB cut to fit box.

The U421 USB interface can drive one or two low-current LEDs directly. But several of the LEDs I chose are not low current, and using a driver to pump a little more current through the LEDs will make the bright ones very visible from way over in my lab. The U421 provides 5V from the USB port. In the photo below the U421 was mounted on the PCB along with the ULN2803. Resistors will be mounted and connections will be made on the bottom of the board.

U421 and ULN2803 soldered in place.

U421 and ULN2803 soldered in place.

The bottom of the board with the U421 and ULN2803 in place will be mounted to the shell of the box that has the LEDs.

Bottom of board with components.

Bottom of board with components.

The LEDs that I picked for the project are each a unique color. I’ll assign an email account to an LED that will flash on each side of the box.

LEDs for project.

LEDs for project.

The LEDs are easy to mount in a 1/4″ hole when these little mounting rings are correctly employed.

LED mounting rings.

LED mounting rings.

Eight LEDs are placed on one half of the box with the leads bent toward where the PCB will be. It was an adventure poking all 16 leads through the printed circuit board.

LEDs and rings in box.

LEDs and rings in box.

With the LEDs in place, and the PCB navigated onto all of the LED leads, the LEDs are then soldered in place.

Board and LEDs ready to be soldered.

Board and LEDs ready to be soldered.

The connections for the components are made on the bottom of the board with wire-wrap wire. A soldered-in-place component on the top of the board leaves a small pyramid of solder on the component leads. When wire-wrap wire is used for making point to point circuit connections, a very small bit of the wire insulation is removed from the ends of the connecting wire. The “pyramid” of solder is melted and the wire wrap wire end is poked into the melted solder.

Wiring complete on PCB.

Wiring complete on PCB.

One 8-bit port of the U421 is used. Each of those 8 lines leads to an input of the ULN2803. The outputs of the ULN2803 connect to each of the LEDs through a 330 ohm resistor. The anodes of the LEDs connect to the 5V line on the U421. Ground on the ULN2803 connects to the U421 ground pin.

The finished Mail Light electrical hardware is assembled and tested with the output test application from USBmicro.

Finished box.

Finished box.

The Mail Light will mount on the back of one of my LCD displays. I modified a straight stock aluminum bar for this.

Aluminum bar.

Aluminum bar.

The bar needed a short 1″ section bent. This I did by putting the bar in a vise brake.

Bending the bar in a vise.

Bending the bar in a vice.

The bent section of the aluminum bar will be screwed to the plastic box.

Bent aluminum bar.

Bent aluminum bar.

On the bent 1″ section of the bar I tapped a #4-40 hole. One half of the plastic box – the half without parts – will have a little hole in it for the screw. I also drilled holes of appropriate size and spacing on the long part of the aluminum bar for mounting on the back of my LCD monitor.

#4-40 screw and tapped hole.

#4-40 screw and tapped hole.

The plastic box half was tightly attached to the aluminum bracket and then the box was reassembled.

Box shell attached.

Box shell attached.

Mounted under my monitor and plugged in to USB, I was able to use the USBmicro output test application to verify that the regular LEDs were visible from a sitting position at my desk, and that the super-bright LEDs facing “back” were easily visible in my lab.

Mounted under monitor.

Mounted under monitor.

The hardware is functional and mounted. Part 2 of this project will be creating the software needed to check my email server for email in four different accounts and illuminate the LEDs.

If you have any questions about this or any other of these projects, please feel free to create an account here (your email address will be kept private) to post.

=Gizmo=

Part 1
Part 2
Part 3
Part 4