Humidity Sensor PICtail Demo Board
The Humidity Sensor PICtail Demo Board (PIC16F690DM-PCTLHS) measures the capacitance of a relative humidity sensor plugged into the board. The on-board microcontroller sends the measured and calculated relative humidity (RH) to a PC for display. The board can also measure small capacitors in different ranges of values using a dual slope integration method. The board can be modified, if desired, to achieve better measurement resolution.
The ambient relative humidity changes the capacitance of the humidity sensor (HS1101LF from Humirel). This sensor is connected to a MCP6291 op amp and a resistor to form an inverting (Miller) integrator. The PIC16F690 microcontroller sends a square wave to the input of the integrator, which the integrator converts to a triangle wave at its output. The firmware controls the magnitude of the triangle wave and measures the integration time. The microcontroller measures the time it takes for the triangle wave to rise and fall. These times are converted to a capacitance value.
A 14-pin header is provided for connecting to the PICkit 1 Flash Starter Kit, which acts like a docking station. It includes a two-wire serial bus that transfers the data, and two more wires for board power (+5V and GND inputs). This interface also supports programming of the on-board PIC16F690. The +5V single supply voltage from the PICkit 1 Flash Starter Kit board is bypassed with two bulk 1 μ F capacitors near the header, and two local 0.1 μ F capacitors (one for each Integrated Circuit (IC)).
A 6-pin header for ICSP (In-Circuit Serial Programming) is available as an alternate interface for programming the on-board PIC16F690. This allows the user to modify the program that comes with the Humidity Sensor PICtail Demo Board (with the MPLAB ICD 2 or PICkit 2 microcontroller programmer).
Key Applications: Humidity Sensing
Features
- Simple interface to a PC using the PICkit™ 1 Flash Starter Kit
- GUI program displays capacitance and Relative Humidity results
- Can program the on-board PIC16F690
- Sockets for inserting radial leaded capacitors
- User selected capacitance range
- Test points to monitor circuit’s operation
- ICSP™ connection gives alternative for programming the on-board PIC16F690:
- PICkit™ 2 Microcontroller Programmer
- MPLAB® ICD 2
Ships With
- Humidity Sensor PICtail Demo Board - This is an assembled and tested Printed Circuit Board (PCB).
- CD-ROM - Provided separately in the shipping box; it contains the files and literature.
- Humidity Sensor (HS1101LF) - Provided separately in the shipping box.
- Bag of Capacitors - Provided separately in the shipping box. These capacitors are provided for the user's convenience; they make it easy to try out this board's functionality, and to verify its accuracy