Steps

1. Evaluation - First of all, make sure you really want to get into this project. It's really not too difficult and not much of a risk of money involved but it does help to have a few key tools and there are some setup costs in the board etching chemical. The trickiest part is making the circuit board. If I had more time, I'd make and sell them or get a batch made but right now I just don't. I find this kind of stuff fun though so if you're a curious tinkerer, the circuit board creation can be fun and an expansion of your skills.

   The creation of the circuit board involves printing a transparency, exposing the board, developing the board, cutting the board and finally, drilling the board. This video shows the process.

   There really isn't anything special required for the developing and etching but you will want to make a jig for the exposure. I will admit though that my etching step didn't completely work my first time out. I don't know if I'd attempt the drilling without a drill press. The bits are so small that they would probably break without a fixed press.

   Beyond creating the circuit board, you're really only soldering components. The tiny displays can get a little tricky since the contacts are so close together. I would definitely get some really fine solder to do this.

   Just to be 100% up-front, I made some slight changes (improvements) to the cricuit board after I made the first one and have not tested the board itself. If there are any issues at all, I will do what I can to help get it working.

2. Order parts - To order the parts, you will first have to make a couple decisions.
   1. Do you want a battery power on the board or power from and external source? The onboard battery means less wires running but the batteries are a little expensive and won't last as long as an external pack. I ran wires from mine to a battery pack in the jet pack.
   2. Do you want a switch on the board or not? If you have the onboard battery you will need the switch but you may not want it if you have an external source. My battery pack in the jet pack has a switch of its own.
   Use the list below to work up your order.

3. Print the circuit board - To print the circuit board, you first need a transparency made from this PDF file. I brought mine to the local Fed Ex Office and paid $.81 cents for a single tranparency print.

   There are multiple boards on this printout and you will want to use two of them overlayed to get a more opaque sheet for the exposure of the circuit board. What I did was pick a common corner and cut those on the exact edge of the board so that I could line them up on in a little jig I made for the exposure. With the one corner cut tight, you can leave the other ones long and just register the two images and tape on the longer side.

   Prepare a jig like the one in this picture using a piece of glass to press the image against the board then expose the board to light as stated in the board manufacturers instructions. The white pieces in the image are some 1/16" pieces of scrap plastic that serve as a shim for the glass.

   Follow the manufacturer's instructions for the developing and etching. One thing that wasn't clear to me in the instructions is that the boards come inside a light proof sleeve but the board itself has an opaque sticker on it that allows you to cut the board before exposing it if you want to. Make sure to take this off before you expose the board.

   Drill the boards before cutting them so that you have more to hold on to while drilling. The bit sizes I used were #60 and #65. You can tell by looking at the parts you get whether to use the larger or smaller bit. The final product involves a main circuit board and a small display board so that the thinner 7 segment displays can be raised to match the height of the LEDs. The image includes four display boards but you only need one so pick the best one and only drill that. These holes are very close together so definitely use the smaller bit. Again, I don't advise trying to do the drilling with a hand held drill but that's your call.

   Cut the boards with a band saw if possible but you can probably get away with a hacksaw if you're careful. The board

4. Solder components - When soldering the components, the rule of thumb is to solder the least heat sensitive components first. So, you could do them in this order:
   • jumper wires
   • switch
   • resistors
   • capacitors
   • ICs
   • LEDs
   • 7 segment displays
   You shouldn't have a problem with damaging any of these components, just don't leave the soldering iron on longer than you need to.

   When soldering the parts, keep in mind that some parts are directional based on polarity. Resistors are not directional but the capacitors, ICs and LEDs are. Capacitors have their negative lead marked and both go directly to ground so trace the group lead and orient the capacitors accordingly. The ICs have a small half circle on one end on the top that indicates pin 1 is on that side. The board will have a "1" where pin 1 is. Just put the half circle end of the IC where the 1 on the board is. For LEDs, the "cathode" or negative side just needs to be connected to the lead that runs to "R3". If you look in the LED, the cathode side is the "L" shaped side. It will usually have a shorter lead. See this link for more information.

5. Test - Once all the components are soldered in you can do a quick test of the main board without the display board installed. Just connect the power and see if the LEDs cycle through the pattern in the video above. If there are any issues at this point, resolve them before soldering in the display board.

   Test the display board for any shorted connections. Being that the traces are so close together, solder can easily be crossing connections or even some traces are may not be fully etched. To test, first solder some 1" or so lengths of full stripped wire to the larger pads on the board. Connect the 5 inner pads to positive 6 volts then using a 470 Ohm resistor, from "flash" to ground, make sure that all the segments intended to flash are lit. Do the same test with the "on" pad. Resolve any shorts with the soldering iron or a knife to cut between traces and break shorts. A desoldering vacuum pump can be fery handy but you use a little piece of frayed wire to clear extra solder.

Tools

• Soldering iron
• Solder
• Wire cutters
• Band saw (for cutting circuit board - hacksaw should work)
• Drill press (for drilling circuit board - I wouldn't drill the small holes without a mounted drill)
• Plastic or glass (not metal) containers for developing and etching. I used plastic sandwich holders with tops on them for storage.

Parts List

Everything can be purchased at Jameco but the resistors are sold in minimum orders of 100 for $3 while Radio Shack sells 5 packs for $1.19. But, shipping may (or may not if you walk into Radio Shack) negate the savings. Or, Jameco has a 200 piece resistor grab bag. Anyway, you can decide what you want to do there.

The main thing that is really specific and not likely to be found anywhere else is the micro displays.

Code	Name/Link	Quantity	Price	Notes
Micro Display	Micro 7 Segment Display	5	$2.99
U1	LM555 IC	1	$.25
U2	CD4017 IC	1	$.45
S1	PCB mount switch (optional)	1	$.39
C1 & C2	10uF Capacitor	2	$.60 (for 10)	Minimum order of 10
R1	100 ohm resistor	1	$1.19 (for 5)	Minimum order of 5
R2	100K ohm resistor	1	$1.19 (for 5)	Minimum order of 5
R3	470 ohm resistor	1	$1.19 (for 5)	Minimum order of 5
R4 & R5	220 ohm resistor	2	$1.19 (for 5)	Minimum order of 5
J1 - J4	22AWG solid wire	1	$7.95	For jumpers
3V Battery	3V Button Cell Battery	2	$1.79	Optional
Rectangle LED	Rectangle LED	5	$.99 (for 10)	Minimum order of 10
Battery Holder	2 Button Cell Battery Holder	1	$.79	Optional
Battery Holder	4 AAA Battery Holder with Switch	1	$1.45	Optional
Circuit Board	3" x 4" Circuit Board	1	$5.49
Etch Solution	9oz Bottle Etch Solution	1	$9.95
Developer Solution	6oz Bottle Developer Solution	1	$11.95