How do you bring power to a AVR 28 pin Development Board?
The first method is to use the power supply block and a wall wart.
The schematic for the power supply is shown below. The 100nF capacitors, resistor and LED are optional. The 100nF capacitors are there because the bigger electrolytic capacitors have a high Equivalent Series Resistance (ESR). This make them a bit sluggish, so we add the smaller ceramic capacitors to provide faster response.
You need to ensure that the wallwart supplies enough voltage. The 5V power supply kit includes the L7805 voltage regulator which has a dropout voltage of about 2V. This means that the voltage supplied from the wall wart must be at least 7V (5 + 2). If you wish you can use other voltage regulators, but you need to ensure that you use one with an IGO or GOI pinout.
Next we have another variation. Instead of a 2.1 x 5.5mm DC Jack we use a 2 Pin Polarized Header with right angle leads. This connector is a bit more compact and the lower profile can come in handy when building a multi board stack.
Now we do away with most of the power supply parts. We use a USB to DC Barrel plug (2.1 x 5.5mm) cable to bring 5V power from a computer’s USB port or iphone charger straight to the board.
You will notice that we have run a small piece of wire from a hole near the positive connector on the barrel jack to the positive power rail to bypasses the regulator circuit.
We keep 2 of the capacitors, a resistor and the LED from the previous power supply circuit.
When building circuits with this sort of power source, connect the USB to DC Barrel plug (2.1 x 5.5mm) cable to something expendable like a USB hub or iPhone charger until you are 100% certain that everything is working correctly. You might also consider using a PPTC Resettable Fuse
Many of the 28 pin AVR microcontrollers can run on voltages as low as 2.7V. Some of the newer ones go as low as 1.8V. This makes CR2032 button cells an ideal power source for low power applications. They are very compact and the 20mm coin cell holders fit right on the board.
As in the previous example we include 2 of the capacitors, a resistor and LED.
The diagram below shows the exact placement of the 20mm coin cell holder.
These examples are of course just scratching the surface. There is bound to be many more ways to power your project. Let us know what you’ve tried.