The easiest way to supply the circuit would be to add a simple USB cord to it and make the users plug it into a USB power supply. The finished device, however, also requires power. So far, I’ve covered the logic portion of the circuit. Designing the power supply for this project In a later revision of this project, I also added capacitors close to the power pins of both ICs to prevent brown-out issues (See part five of this series for more details). I, however, forgot about this header when ordering the PCBs, so I’ll have to add the buzzer manually in the end. And, lust but not least, there’s an additional pinheader for connecting a buzzer that alerts the user when the timer reaches zero. Note how each sensor output also incorporates a 36 megaohm resistor. Other than the MCU, figure 2 also shows the headers that I’ll use to connect the Arduino to the metal plates of the capacitive sensor. In my case, however, there will be no physical buttons that the users can access. Pulling the reset pin of the MCU low resets the microcontroller, and you could add a reset button here to allow users to reset the device if it hangs up, for example. Besides that, note how the reset pin is constantly pulled high via a 10K pull-up resistor. The external oscillator ‘overrides’ the internal clock in either case. Some ICs, especially the cheaper ones, might omit this internal oscillator, so I like to be on the safe side and add an external one just in case. However, that’s not the case for every manufacturer. Some ATMega328PU chips actually don’t even require this external crystal because the IC might have an internal 8 MHz oscillator. This setup also requires two 22 picofarad ceramic capacitors. 2 contains an external 16 MHz crystal that serves as the input clock for the MCU. Running an Arduino MCU without the Arduino board itself only requires you to add a few external components. Anyway, the main attraction in figure 2 is the MCU, which is an ATMega328PU (i.e. Note that the three lines that go off the top of figure 2 connect to the three lines that come in from the bottom of figure 1. Here’s the second part of the schematic that shows how the ATMega328PU fits in: Figure 2: The ‘Arduino’ part of the circuit Please double check them if you’d like to build this project at home! How to use only the MCU of an Arduino in a DIY projectįigure 1 only showed a small part of the circuit. That means that the connections between the controller IC and the displays might not be correct in your case. Note that the pinouts of the seven-segment displays in EAGLE didn’t match the real ones I’m using. Overall, I think this solution will work just fine in this project. Anyway, this also means that I only had to connect three I/O lines of the Arduino to control both seven-segment displays, which is a huge benefit as well. The downside to this approach is that the software will have to be slightly more complicated and that the MAX7219 is relatively expensive. However, I found that employing the MAX7219 leads to an overall smaller circuit as this method means that I’d only need to add a single IC. Initially, I planned to use two separate controllers and let them interface one display respectively. The MAX7219 seven-segment display driver does the heavy lifting here. 2 only shows the display section of the circuit. Anyway, I gave it my best, and I hope the following circuit will be up for the task at hand: Figure 1: The display part of the schematic Keep in mind that I’ve never worked with this type of circuit before, and I generally also don’t take capacitance or any advanced topics into account when designing a circuit, as I’m simply not a professional by any means. This ensures that the finished device can be as small as possible, while it still gives me the convenience to use simple tools, such as the Arduino IDE, to write the firmware for this project.Īside from that, the circuit also contains the previously mentioned resistors and traces that will connect the Arduino to the metal contacts of the capacitive touch sensor in the finished project. Designing the main circuit for this projectĪs mentioned in the last part, I decided to use only the MCU of an Arduino Uno in this project.
0 Comments
Leave a Reply. |