Whilst most people considered the CP a good CPU, it had one significant problem; to reduce pin count of its physical DIP packaging, the address bus and data bus shared pins. This meant that communicating with a device required the device to watch for key memory locations being accessed on one machine cycle, and then read the data on the next. All of this complexity was repeated on the CPU side in the corresponding device driver. To address this shortcoming of the , the 8-bit PIC was developed in
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Among other useful features this IC has built in brightness control and scan control capability that allows to limit the number of shown digits. Arduino version available at this link.
See MAX datasheet for more detailed information. As you can see from the schematic of this circuit it does not have any inputs. I just wanted to show how to communicate with MAX using a simple function. Current code outputs 10 digits every second to MAX in order to produce a simple counter shown on 7-Segment display. See attached assembly code for additional information. These modules can be purchased on Ebay in different configuration, you just need to connect a microcontroller.
Hopefully you can use this design as a basis for more advanced projects. BCD code is identical to a binary representation up to 9 therefore requiring 4 bits for each digit. Decoder will ignore higher value inputs. Schematic and source code are available on the next page. If you are going to build this circuit pay attention to how they are connected to controller.
PICkit3 programmer was used to download the code but I did not want to overload the schematic with too much information.
Source code and a compiled HEX file can be downloaded here. Response Time Meter If you ever thought how fast you can react to external stimulus here is the circuit that can measure your response time.
The average human response time is about ms. The principle of operation is relatively simple. Next the program counts the number of millisecond pulses until the switch is pressed and this is your reaction time. Here is the schematic. Source code for this design was written for PIC16FA micro controller in assembly language and can be downloaded here.
In the following figure you can see a prototype constructed on a standard breadboard. A few words about limitations of this project and possible future improvements. Currently the time it takes to turn the LED ON is not random, so implementing a random number generator routine can be a useful upgrade. Electronic Lock Here is a modified and improved electronic lock design.
For Arduino version click here. In order to open the lock all 4 digits must be entered in correct order. Here you can see a short video showing electronic lock prototype design operation. Source code can be downloaded at the bottom of the page. For simplicity reason only of available bytes are used.
To test circuit functionality connect the signal source to AN1 input and Scope to digital to analog converter output. Press Record push button to record one cycle of the wave. Now you can disconnect the generator. Press Play to output one cycle of the recorded waveform. Signals in the lower KHz range seem to work OK. Next figure shows the schematic of this simple design.
Limitations and possible future improvements of current design: A better synchronization routine is needed in order to avoid glitches while reproducing the recorded waveform. The beginning of the next cycle should start exactly were the previous cycle has stopped.
Source code is here.
Descripción del PIC 16F877
Interfacing MAX7219 with PIC16F876 microcontroller