Frequency Meter for 10 Hz to 100 kHz Input by 74121

Description:

This frequency meter is suitable for sinusoidal wave and square wave input signals. Minimum input potential must be 25mV(rms). Measurement range can be determined from 10 Hz to 100 kHz by using the S1 switch. Each switch position part is calibrated by using 20 kOhm potentiometer. Total current consumption of the circuit is about 10mA. R1 and C1 values should be chosen depending on wheather microampermeter or milliampermeter is used.

Electronic Thermometer Project by LM35 and LM3914

Description: 

As shown in the schematic, temperature sensor of our electronic thermometer is LM35DZ. There are some kinds of LM35 IC, since it is cheap and easy to find we used LM35DZ in our project. It measures from 0°C to 100°C with a very linear output graph. For one degree change, it increases its output 10mV.On the other hand, this circuit measures temperature values only between +10°C and +39°C.

2 numbered (middle) pin of the sensor is connected to the 5 numbered pins of LM3914 ICs. So every IC determines how many leds of bargraph will bright due to the analog  signal received from the sensor. 2.2 microfarad tantal capacitors are connected between the 2 and 3 numbered pins of LM3914. Resistors in the circuit have %1 tolerance values...