This is easy to build a simple digital thermometer with only two parts – microcontroller, temperature sensor and display. Here is one small project that can be put together in less than hour.
It is based on PIC16F628A which reads temperature from DS18B20 1-wire digital sensor. Temperature is displayed on four seven segment display which can output temperature values from -55 to 125 degrees. Probably most work that needs to be done here is interfacing the display which cathodes are switched though BC337 transistor keys. The keying is needed to dynamically switch between separate digits. This way less microcontroller pins are required. Source code is ready for download so all you need is to plug pickit3 or other programmer and have temperature output immediately.
The schematic is fairly simple and straightforward and uses a PIC16F628A microcontroller for measuring frequency and a high speed comparator for signal amplification and conditioning. Timer0 is used to count the input signal at pinRA4. In order to achieve the maximum possible resolution, the input signal is probed for 0.125 seconds and the prescaler value is computed accordingly. The input of the schematic is feed through a high speed comparator.
The two inputs of the comparator are set at about 1/2 of power supply voltage with 15-25mV difference between them so any AC signal with higher voltage will start switching the comparator. The input is protected with 1k resistor and two diodes limiting the voltage to ±0.7 V. The input impedance for low frequenciesis equal to R1 – 47k. For VHF range maybe it is good idea to replace it with 50Ohm value. The schematic have fairly low power consumption – with no input signal the supply current is 7-8mA and goes up to 20mA with 200+MHz input signal.
Probably most of you know that ESP8266 can be used as WiFi connectivity module or as stand alone programmable device with same internet features. Anyway for serious applications probably it is best to use it as module along with another microcontroller. Electro-labs have shared pretty neat development board based on PIC18F microcontroller which comes with buttons, LEDs, LCD, FT232RL based USB connectivity and integrated ESP8266 module.
WiFi module can be controlled by microcontroller or directly from computer via FT232RL chip. Normally ESP8266 module is controlled with AT commands sent from microcontroller or from computer terminal.
Jordan started this binary watch project to gain more experience in programming PIC MCUs for low power applications. But it turned out pretty successful that after wearing it for about a month he started selling them for everyone.
As we mentioned, binary watch is based on PIC18F24J11 microcontroller which drives bright LEDs on display for each binary digit. Having bright LEDs installed he was able to dim them and this save power without loosing brightness. Watch is powered by CR2032 coin cell battery which is enough for 3 months of usage. Special care is taken to make watch as low power as possible by combining several MCU sleep modes. He found interesting solution to watch clasp. He used same programmer ribbon cable and secondary non electrically connected header on other edge of board. It really looks great and there are no redundant parts.