This battery tester circuit is designed using the LM3914 integrated circuit and some electronic components. Battery voltage is compared with a reference voltage obtained from an internal source. Reference voltage (pin 8) can be set between 1.5 V and 2.7 V, R1-R2-P1. Potential voltage pin 8 be the head scale LED string. This means that if the voltage is 1.5 V, each LED will symbolize a voltage of 150 mV. We recommend setting the reference voltage from 1.5V NiCd battery, 2.0 V for dry battery. The resistor R1 sets a current of 12.5 mA for each LED.
Using this circuit diagram can be designed a very simple logic tester consists of two comparators, the system works with different reference voltages supplied by different voltage dividers. R3-R4-R5 divider provides a voltage of about 40% from Ucc voltage, pin 6 of IC1b, and an approximately 16% of Ucc, pin 3 of IC1a. When Ucc = 5 V, the voltage is exactly the threshold comparators TTL (0.8 V and 2.0 V).
Similarly, R6-R7-R8 divider voltage supply 23% and 73% of UCC's IC1a pin 3 respectively IC1b's pin 6 (the standard threshold levels correspond CMOS comparators).
Using this circuit diagram can be designed a very simple electronic tester for quartz crystals. At this tester for quartz crystals a LED indicates if crystal tested oscillate or not .Tester was designed primarily to be used to test crystals with fundamental frequency between 1 MHz and 30 MHz.
Many crystals in the range 1-5-4 MHz oscillate easier when switch S1 is closed.
The typical current through the tester does not exceed 30 mA at a supply voltage of 9 V