TAILIEUCHUNG - Practical Arduino Cool Projects for Open Source Hardware- P22

Practical Arduino Cool Projects for Open Source Hardware- P22: A schematic or circuit diagram is a diagram that describes the interconnections in an electrical or electronic device. In the projects presented in Practical Arduino, we’ve taken the approach of providing both a photograph and/or line drawing of the completed device along with a schematic. While learning to read schematics takes a modest investment of your time, it will prove useful time and time again as you develop your projects. With that in mind, we present a quick how-to in this section | CHAPTER 11 OSCILLOSCOPE LOGIC ANALYZER Figure 11-3. Schematic ofArduino Oscilloscope Logic Analyzer 0 1 2 3 4 5 6 7 Instructions The circuit for this project couldn t be much simpler. It s essentially just an Arduino with probes connected to a number of analog and or digital inputs with all the hard work done in the software plus a power LED to show when it s alive. In our prototype we fitted a total of eight input probes but because the Duemilanove and most other Arduino designs only have six analog inputs we connected the first six probes to the analog inputs and the remaining two to digital inputs. This allows up to six analog waveforms to be sampled which is plenty for most applications but still allows up to eight digital lines to be analyzed in case we need to process an 8-bit parallel data bus. Alternatively you could use an Arduino Mega and take advantage of the fact that the Mega has 16 analog inputs. Just keep in mind that the more analog inputs you want to sample the slower the program will run and the lower your sample frequency will be. Or if you only care about sampling one or two channels at a time you could simplify things and leave the rest of the inputs off entirely. You could even use an Arduino Pro Mini and build the whole thing into a large probe body to create a single-channel handheld device with a USB connection on the back. Bluetooth or ZigBee comms to the host computer would also be a possibility so that you could make it totally wireless. It s really up to you to decide how you want to configure it. You ll note that we specified a metal project case and shielded cable for the probes. This is to reduce cross talk where a signal presented on one input influences the readings of other inputs by inducing 189 CHAPTER 11 OSCILLOSCOPE LOGIC ANALYZER tiny currents in them. You can certainly do without it but you may see a signal in one channel cause artifacts in the display for other channels. You ll also note that we didn t bother including any

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