how to add buzzer to LM3914 voltage level indicator circuit ?

Thread Starter

bigjoncoop

Joined Feb 1, 2019
158
i've been making some Battery Voltage Indicators using LM3914 IC"s... (Schematic Below)

Im working on a project that needs to have a Audible Alarm when the voltage drops below ~10v and also needs to have a voltage level indicator, so i'm curious if its possible to simply implement it into the same circuit to save some room and if so how...

normally I would use a LM358 IC to create a low voltage alarm. (Schematic Below)

*This project will have a momentary push button to activate the LM3914 Voltage Indicator but the Audible Alarm needs to always be active

so if anyone knows the simplest way to go about this, i would greatly appreciate it. Or if im better off just keeping the 2 separate
THX

LM3914 BATT INDICATOR.JPGLM358 VOLT ALARM.JPG
 

crutschow

Joined Mar 14, 2008
27,170
If one of the LM3914 output LEDs light at the desired low voltage then you can use a PNP transistor (e.g. 2N3906) to turn on the buzzer.
Connect the transistor emitter to the plus voltage, a 4.7kΩ resistor between the base and the the desired LM3914 LED output, and the collector to the buzzer circuit to ground.
 

Thread Starter

bigjoncoop

Joined Feb 1, 2019
158
If one of the LM3914 output LEDs light at the desired low voltage then you can use a PNP transistor (e.g. 2N3906) to turn on the buzzer.
Connect the transistor emitter to the plus voltage, a 4.7kΩ resistor between the base and the the desired LM3914 LED output, and the collector to the buzzer circuit to ground.
thx @crutschow

so i would have run the LM3914 in dot mode instead of bar graph mode. Oh but since im using a button to trigger the lm3914 indicator this method wont work since the Audible Alarm needs to always be active.

but i will def add that simple circuit using the single transistor to my circuit library .

thx again
 
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