Newbie here with a question on developing a flashing circuit based on the LM3914 chip.

The NS datasheet includes a flashing circuit using a single LM3914 chip. I'm building a circuit using three LM3914 chips to drive 3 x 10 LED bar graphs (30 LEDs in bar mode - I have a jones for light bars). Anyway I want them (all 30 LEDs) to flash when the signal voltage exceeds 10 VDC. The single chip method taps into pin 18 then through a cap and resistor to the pin 8 junction with resistor after pins 6 & 7. This did not work with all three chips. Any hints/help/snide comments?

thanks

 

If you just want all the LED's to go at 10 volts, a single compatator is all you need.

 

please be more specific? Where would I put the comparator, and what comparator? I've attached both the National Semiconductor drawing and a drawing of my circuit for any help.

Thanks

 

How are the three circuits connected together?

 

No guarantees, but see the attached.

The idea, with a single unit, is that when the top LED comes on, its cathode goes low and pulls-down on the HI reference which causes all the leds to turn on. The cap charges and discharges accordingly and the top LED cathode alternates between Hi/Lo.

The problem could be the daisy-chain of the HI ref into the LO ref of the next unit, which means the added circuit will be pulling down on both references and it won't flash.