The Rainbow kit includes an instruction sheet so I will not duplicate the construction here. There are three versions that you can build; a 5V, 8V, and 12V model - and parts are included for all three. Obvously, you want to build the 12V model, so make sure you use the proper instruciton sheet (VM2-12). When soldering, use no more than a 30Watt soldering pencil.
The kit comes with two RED LEDs, two YELLOW LEDs, and four GREEN LEDs, and suggests placing them as shown by the left drawing. However, I modified the color pattern as shown on the right. This required the purchase of an additional RED LED. Take one of the LEDs to your local Radio Shack store and have them find one the same size for you.
When you install the LEDS, they can only be inserted one way. There will be a flat spot on the LED itself, and one of the two leads will be shorter. The short lead is on the side of the flat spot. This lead goes on the circuit board where the flat spot is silkscreened onto the board.
I Also used nylon spacers (the white cylinders under the LEDs in the photos) so that I could easily line up the LEDs. These spacers are not included in the kit, but can be purchased from www.mouser.com or www.digikey.com.
Pay particular attention to the diodes, as they must be inserted one-way. On the circuit board, there will be a solid white mark silkscreened where each diode goes. The diode will also have a band on one end - shown here as a black band (however, some diodes may have a white band). The band on the diode must match the band on the circuit board as shown.
You will also find two Zener diode in the kit, with a voltage marked on it. One will be marked 5.1V, and the other 1.5V. For the 12V kit, you will use the 7.5V Zener (the 5.1V zener will not be used). Be careful as these diodes will look similar to the others, but they are different.
Here the kit is completed except for the insertion of the Integrated Circuits (IC). Leave those for last.
I have provided a large photo of the board which you can access by clicking HERE.
Compare your board to this board to make sure everything is in the correct location and orientation. Pay attention to the stripe colors and sequence on the resistors, as they color-codes determine their values.
When you are satisfied everything is correct, you can finally insert the ICs into their sockets. The ICs have a notch in one end, and must match the notch in the sockets.
To test the monitor, you will need to connect it to a 12V power supply. It would be helpful if you had a precision variable power supply like the one shown so that you can vary the input voltage. However, if you don't, you can use a 1K potentiometer @ 1/2Watt (available at Radio Shack), wired in series with the input. This should allow you to vary the input voltage so that you can adjust the board.
To adjust the board, simply monitor the input voltage with a voltmeter, and set it to 11.64V (or any other point you want to calbrate). Then turn the on-board potentiometer until the desired LED turns on - thats it.
Notice that with the Rainbow monitor, each LED turns on in succession. At the lowest voltage, only one LED will be on, but at the highest voltage, all 7 LEDs will be on. This results in a maximum current requirement of 140mA. While this is not a lot, it is enough that it could drain your battery in a few weeks. Therefore, you will want to control this monitor with an on-off switch.