Milestone+2+-+Umair

toc =Power Supply=

Efficient power supply is the cornerstone to the success of robotic project. It provides the power source to servo motors. Just using battery will not do the job. In fact, there are come rules that need to be taken under consideration before making continuing. We need a circuit that regulates desired voltage, supply the required amount power at all times, and allow for additional special requirements of particular application:

Regulate at a set voltage
For efficiency, optimally it would be best to use a power source slightly above the desired voltage input required. However this is rarely easy or even feasible. Different electronics require different voltages. A MCU will require 5V, your motors perhaps 12V, a voltage amplifier perhaps both 20V and -20V. Batteries are never at a constant voltage. A 6V battery will be at around 7V when fully charged, and can drop to 3-4V when drained. This below image shows how a typical battery voltage changes over time.



To correct for this, an IC module called a voltage regulator is used. What a voltage regulator does is take any input voltage and outputs a regulated voltage. So if the battery is at 7V, then a 5V regulator will output 5V and rest will dissipate as the unused energy/heat. To calculate wasted power, use this equation:
 * (input_voltage - output_voltage) * current = wasted power **

Since MCU and sensors typically do not consume that much current, the wasted energy isn't that much. But for motors, this can be a huge problem. We do not want to over voltage them, but to regulate the voltage is a huge waste of energy. To correct for this, instead is switching regulator used. They act just like a voltage regulator in terms of output, but are much much more efficient.

Supply a minimum required amount of power
The sum required power of all servos needs to be below the amount the power circuit can supply. If power drops even for a fraction of a second below what the servos require, things like the MCU could reset, or sensors would give bad readings, or motors wont work very well. The rule of thumb is:

**Energy required by robot** **< Energy battery can supply**

To solve this problem, we determine how much total power servos will require by experimenting, calculating equations, and looking up datasheets of the servos and other parts used:
 * power = voltage * current **

**Additional Features**

 * Short circuit protection
 * Regeneration
 * Negative voltages
 * Noise protection



= = =Proposed Components=


 * [|Switching regulator - 3 Amp Adjustable Switching Regulator (DE-SWADJ 3)]
 * ATX Power Supply (PSU)

=Theory of Operation=

We proposed ATX PSU as power source because it is relatively cheap. Along with that we get huge current outputs, short-circuit protection, and a very good voltage regulation. Generally PSU give 5 V, 30 A, and 12 V, 12A, supply. These rating can easily replace standard lab power supply.

In order to convert PSU to our power supply, we need to first identify which wires are 5 V, 12 V, and GND, etc. The 5 V rail can be used as it is since it already regulated to 5 V. In addition to that we proposed an additional fuse, on/off switch, LED, and a capacitor to take out any transients. The 5 V supply will provide power to MCU and sensors. On the other hand, the 12 V rail need to be regulated to around 6~6.5 V to provide power to servos. Its schematic is identical to 5 V except it has an additional switching regulator. The switching regulator is similar to regular voltage regulator but it is much more efficient. A regular voltage regulator may burn and melt due to overwhelming power requirement. This is where switching regulator comes.

Before choosing the switching regulator, we found the total power consumed in worst case and it was about 93 Watts for all 10 servos. We propose 3 Amp Adjustable Switching Regulator from Dimension Engineering, model DE-SWADJ3. It should be ideal for our application as it provides maximum of 25 Watts and an adjustable output voltage from 3 to 13 V. Using this switching regulator with four 12 V rails should provide ample power to the servos.