Wind Speed & Direction Meter with a Clever Touch （2）

Published:2011/7/26 2:04:00 Author:Amy From:SeekIC

G.Samblancat

Block diagram

No remarkable things are seen in the block diagram in Figure 2. The start­ing point is the pair of Hall sensors arranged at an angle of 90 degrees.



Two amplifiers, one for each sensor, condition the sensor signals for use by an ADC and then on to the processor. The ‘limiter’ block prevents overdriving of the capture/compare input on the PIC16F876. The processor is also busy driving the LCD as well as outputting an NMEA compatible serial signal for use by a PC or suitable navigation equipment. That wraps it up as far as the block diagram is concerned and we’re ready to have a look at the

Circuit diagram

The schematic in Figure 3 can not be said to be overly complex, can it? At the heart of the circuit we find a PIC16F876 and a double opamp. There’s a 218-page document on the PIC family waiting to be downloaded from the Microchip website men­tioned at the end of this article. The PIC used here has Flash memory and is simple to program over a serial link. On board we find a 10-bit ADC of which two inputs are used, as well as a capture/compare module with one input used to measure the period of the reference signal. Using opamp IC1 (an LM358) the signal amplitude is adjusted for optimum use of the input span afforded by the ADC inside the PIC.



The two UGN3503 sensor chips, IC5 and IC6, are linked to the main board by way of 4-way connector K3. Together with two small loading capacitors, quartz crystal XI provides a 16-MHz clock frequency.

Connector Kl allows the circuit to be hooked up to the PC’s serial port. The LCD drive employs the R/W signal pair, besides Enable and RS, all on con­nector K2. Only four datalines are required in our case as the LCD is operated in 4-bit mode. Jumpers JP1 and JP2 serve to select between NMEA mode (JP1) and CALibration mode (JP2).

The on-board power supply gets its raw supply voltage from a 12-VDC mains adaptor. Alternatively, the instrument may be powered from a 9-V battery, in which case C7 and regu­lator chip IC3 are omitted and a wire link installed between the holes nor­mally provided for the input and output pins of the 78L08.

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