Tuesday, 26 April 2016

Power supply boards

Team:     Mechanical
Author:  Qichao Zhao
Post: #7

In the last sprint, we almost finish the board for power supply, but there is a problem about overheat need to fix. We tried to use different ways to cooling the regulator temperature, it still very hot. But we found that it can work perfectly if it only connects with servo. Then we think to do another power supply board for two of pi. This circuit for pi could turn down the value of voltage to 5v.
The power supply circuit as shown below and we bought some components on the rs-online website.

The LM2575 series of regulators are monolithic integrated circuits that provide all the active functions for a step-down (buck) switching regulator, capable of driving a 1A load with excellent line and load regulation. These devices output voltages of 3.3V, 5V, 12Vand an adjustable output, those characteristic was benefit for this circuit.
The website for calculating the value of output, R1 and R2 are shown below.

Embedded Switch Mode Power Supply
tracopwer 25W, 12V dc, 2.1A
3 port
NOPB Step-Down Switching Regulator 
Schottky Diode
ON Semi 1N5822RLG
Leaded Inductor
Murata 100 μH ±10%
 Resettable Fuse
Bourns 0.9A Radial Leaded PCB 
3.3K ohms
10K ohms
1000u F16V

All of the production steps are similar with board 1 that it was introduce in the previous post. It just made it by different components. When we finish this task, another problem is coming. When two power supply boards were implement, the fixed support should be design for power supply boards. Because no support in the lamp base. It will very handy if we design it.
There are some methods to do the fixed support. First, The PCB boards which the size is same as power supply were cut. Then solder. Two boards together, the one piece of boards was perpendicular to another one. Next, some holes were drilled by electric drill on the power supply boards. Some components on the power supply boards should pay very attention when we used electric drill. Finally, the two boards were tied at fixed supports both sides. The diagram was shown below about board with power supply.

I think we finish the job successfully. But when power supply was connected to pi and servo, we have to connect all of wires one by one by circuit connector diagram. It will damage if we connect to wrong wires. Filipe did lots of stuff  which is similar with this project, we did the cable together.  In order to avoiding those disadvantages, so we decide to make some cables. Lee found the Heat-shrink tube, 9 pin male and female DE-9 connector (plug), wires, soldering iron and solder from Damian's office. Based on the pin diagram, the connector cable was soldered.  In order to tied 8 wires together, the Heat-shrink tubes were set outside of wires. Because Heat-shrink tube was insulated, it could keep our safety as well.

The cable diagram was shown above. When we connect the cable to power supply, it could provide servo and head working at same time. In addition, it also could work if it just connected to head without servo.There are some reasons why we doing this cable are that it can connect easily, it avoiding wires misconnection and disconnection.  Secondly, we put this cable into lamp holder. It looks more beautiful design, which is better than wires outside. 

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