Urban Survivalists

This week we are going to be making the power supply to run the fogger units that you saw last week. Basically, the power supply converts the 120 AC power from your wall outlet to 24 AC the foggers use and the DC that the micro controllers run off of. We know that we want the power supply to be able to work with both the Arduino and Tower micro-controllers when it is finished. Each one has a different plug in for power. The Tower electronics have a mini usb plugin that uses 5V, while the Arduino had the 5mm plug as we learned from the RO system build and needs 12V.

Power Supply

Materials:

The supplies we needed to get this project going are seen in the picture below:

1. Transformer, TR241
2. Nuts, washers, and bolts of same size #6
3. Wire butt splices
4. Wire fork terminals
5. USB to mini usb cable
6. 4″x2″x5″ aluminum box
7. Fuses, 1A
8. Fuses, 0.1A
9. Heat shrink tubing
10. Two 10 position Screw terminal strips
11. Nylon washers
12. On- Off toggle switch
13. 12ft three wire extension chord
14. Wire, 22ga
15. LED panel mounts
16. One LM7812, voltage regulator
17. One LM7805, voltage regulator
18. 5mm power plug
19. Strip board
20. Grommets
21. LED
22. 560ohm resistor
23. Two 100uF electrolytic capacitors
24. Two 10uF electrolytic capacitors
25. Not shown, is a bridge rectifier rated at 400V–which is way to much for us but they were cheap.

Now that we know all the supplies necessary for completing the power supply, we need to start putting it together.

Steps:

In order to start laying out how things will fit in the aluminum box, we took everything out of the packages and started playing around with the location of each item.This will vary for each person’s build, but we thought we found a configuration that would work.So here is the process we used there after:

1. We hooked the output wires coming from the transformer to the screw terminal strip with wire fork terminals.
2. Then we cut the female end of the 12ft extension chord off. Stripped the wires and spliced them to the input wires on the transformer via the screw terminal strip. The ground wire will be the odd man out, though we will use him, as you need to connect to the two wire side of the transformer. This way we can plug the transformer into the wall. See pic 1. This is a good point to test things to make sure you have it wired corectly. The three wires coming out of the transformer are the lower voltage end. The two wires are the ones that need to be attached to the plug. This is very important! Getting this backwards will result in a burned up transformer.
3. We drilled some holes in the case for the LED light, fuses, a hole for all the wires to escape the box, and on-off switch, as well as holes for the screws to attach the transformer, the terminal strips, and the boards. See pics 2-5
4. Then we had to create a board to act as a voltage regulator to convert AC current to DC current at 12 and 5 volts. The schematic for that is below, but it is not shown in the pictures. Opps. We used strip board and just put the bridge rectifier, the two voltage regulators with their two capacitors each as well as the single resistor for the power-on LED. We then used wire to run the inputs and outputs to the terminal strips so that things were slightly more modular. Also, it is a good idea to use a liberal amount of zip ties to keep the wiring from getting out of hand.
5. Once the board was created and the holes were drilled, we placed all the components inside and wired the components together through the terminal strips. See pics 6 & 7.
6. Close the box up and give it a final power test then run get your significant other to see how cool your switch controlled red LED is! Awesome!
7. Done!

1	2	3	4	5	6	7

Here is the schematic for the voltage regulator board:

Here is an image of the final product:

The best part of this whole unit is that it works!  We took the power supply to the local Dorkbot meeting and used it to run the fogger and fan units. It was good times. As a general note, since we didn’t give you exact wiring instructions–that’s just too much of a pain in the butt–the two terminal strips should be placed between the transformer and the voltage regulators and between the voltage regulators and the fuses. This allows us to change stuff and fix it in the future if we so desire. It also lets us take things out of the loop selectively.

Next Week

Next week we will do the prototype control electronics via the Arduino and will continue researching running the system off the Tower micro-controller system.

Thats all for now!

P&S