Digital thermometer based on DS18B20

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.


Con-tactless Thermometer – Pyrometer

The device was designed for con-tactless monitoring of temperature. It is also capable to record the temperature measurements and upload them to a computer via the serial interface.


The device is based on TI’s MSP430RF5728 microcontroller with FRAM type of memory instead of conventional Flash. It needs just 3 external caps to operate (C11 – C13) and uses SPI interface to communicate with μC at 8 MHz frequency.

The device operates in 3 main modes which are selected with a slider switch. The measurements can be stopped and started by the “mode” button which is convenient for monitoring some difficult to access devices. The monitoring period is set with “<” and “>” buttons and is displayed in the bottom right corner of the screen.

Turning the device into the temp recording mode can be done by moving the switch to the top position. In the later case the device automatically shuts down.

Finally, in the bottom position of the slider the device performs playback of recorded values from memory and displays them on the LCD. The images below show the device in operation for all of the main modes.

To upload the recordings into a computer one should turn the device on with the mode button pressed.


Keypad based garage door access

Garage is one place that need to be protected but also has to be convenient to access. When driving in and out a remote control is great choice. SamJBoz had a problem with his remote control so he decided to build in a keypad controlled system based on arduino.


Keypad system uses 4 digit pin codes for opening lock. Each family member has its own pin code. User with master code can enter and delete new users. Arduino Pro Mini sits on a custom PCB which has necessary connections for keypad, Piezo buzzer, LED and other. Eagle files are available for download.


100MHz frequency counter using PIC16F628A

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.