Project 1: Power supply #
Build a breadboard power supply
The first project is to build a power supply that meets the following requirements:
- It consists of a PCB that plugs directly into a breadboard.
- It accepts power from a 2.1 x 5.5 mm plug from a 12 V wall adapter.
- It emits 12 V, 5 V, and 3.3 V (at the same time).
Due date for Printed Circuit Board submission: Wednesday, September 30, 6:00PM
Due date for prototype on breadboard: Monday, September 21, 11:59PM
When your design is ready, you should submit it to the fabricator, OSH Park. It will cost you around $10. After you submit it, take a screenshot of your order confirmation. You’ll need to upload it to the Project 1 PCB assignment on Canvas. That will serve as proof that you submitted your project on time. If this cost is a hardship, please email your KiCad files to your ME 30 instructor, and we will order it for you.
More details for Project 1 #
First of all, we’re not trying to build anything revolutionary in this project. None of you have ever made a PCB before, so the point is to make something fairly simple to get comfortable with the process. If you search Amazon for “breadboard power supply”, you’ll see that you can buy various versions of things like this, though none with a 12 V passthrough, so far as we’re aware.
Here’s what a typical one of these things looks like.
The image below shows the mechanical constraints for the PCB. You can make a board of whatever dimensions you want, but it needs to plug into the breadboard, so you probably want to make sure that the pins line up with the holes in the breadboard, as shown below. You can get by with 4 pins, but 8 will make the board stay in place a little more securely. Regardless of how many pins you use, make sure that each rail has only matching pins, i. e. don’t accidentally connect 5 V to GND.
The dimension between the outer pins is estimated at 1.9 inches. It would be a really good idea to verify that dimension on your breadboard. Sometimes the breadboards are a little wider or narrower.
You can rely on the rest of the dimensions being quite accurate.
In your project kit, you’ll find all the components you’ll need to build a prototype of your power supply on a breadboard. You build the prototype and make sure that you’ve got the wiring right. Then, make the PCB with the same connections. Finally, when your PCB arrives in the mail, you can reuse the prototype components on your PCB.
Important note: the pins on the 5V and 3.3V regulators are not in the same order!
Check the datasheets for the components to see which pin is the input pin, which is the output pin, and which should connect to ground.
If you feel like you understand this project pretty well, or if you’ve made a basic circuitboard before, you could try adding additional features. Look at the open source Ant breadboard power supply for inspiration. The schematics are available if you’re curious about the details.
P1 prototype: what you should try before class #4 (photo of prototype due to Canvas 11:59pm, Mon., 9/21) #
- Read and try to make sense of the website notes on voltage regulation. Pay special attention to the circuit diagram showing the L7805C voltage regulator.
- Try your best to make a breadboard circuit so that 12 V goes into your circuit and 5 V and 3.3 V come out. To get started, see the schematic on the Voltage Regulators web page. You’ll need to use your 5V and 3.3V voltage regulator components.
- Read as much of chapter 2 from the Practical Electronics textbook as you can.