Components Required:
Semiconductors:
IC1 - 7805, 5V regulator IC2 - AT89C2051 microcontroller
IC3 - CD4050, hex buffer T1 - BC547, npn transistor
D1-D4 - 1N4007, rectifier diode D5 - 1N4148, switching diode
LED1 - 5mm LED
Resistors (all ¼-watt, ±5% carbon):
R1 - 1-kilo-ohmR2, R4, R6-R9 - 10-kilo-ohm
R3 - 4.7-kilo-ohm R5 - 150-ohm
Capacitors:
C1 - 1000μF, 25V electrolytic C2, C3, C7 - 0.1μF ceramic disk
C4, C5 - 22pF ceramic disk C6 - 10μF, 16V electrolytic
Miscellaneous:
X1 - 230V AC primary to 9V, 250mA secondary transformer
S1 - On/Off switch S2 - Push-to-on switch
XTAL - 24 MHz
16×2 LCD.
Principle:
The circuit shown measures frequency about 250khz. Frequency meters have always been expensive tools for the average hobbyists. Now, with microcontrollers and liquid-crystal displays (LCDs) having become very economical and popular, it is possible to build a compact and low-cost LCD based frequency meter that can measure up to 250 kHz. A sample photo of the LCD module is shown in Fig. 1. These modules are available in 14- and 16-pin configurations. The 16-pin module has a backlight option. Popular brands are Lampex and Hantronix. Note the pin number sbefore soldering to the circuit. In this project, the LCD module used is Lampex LM16200 with 16 alphanumeric characters and two lines with backlight option. Pin details of this module are given in Table I. A functional diagram of the module is shown in Fig. 2. However, you may use any branded or unbranded 2-line, 16-character LCD module for this project. The10k potentiometer, which controls the contrast of the LCD module, works best when its wiper contact is nearer to ground potential.
Circuit Diagram:
